Met Office Weather Review 2012 - Northern Ireland Environment Link

Transcription

The UK weather
during 2012:
a review
January 2013
Met Office
MetOffice_WeatherReview_2012_Julia
© Crown copyright 2008
-1–
Data provided by
Met Office National Climate Information Centre
.
Contents
Introduction ......................................................................................................................... 2
UK climate overview ........................................................................................................... 3
Overview of the global climate in 2012 .............................................................................. 4
Global warming in 2012 ..................................................................................................... 7
The ‘dry’ season .................................................................................................................. 8
The January windstorm and the Hazard Impact Model .....................................................10
European cold weather and sudden stratospheric warming ..............................................11
‘Spot on’ snow forecast supported by latest Met Office science ........................................12
The ‘wet’ season.................................................................................................................13
Localised summer flooding and the UK ensemble ............................................................15
Olympics 2012 and the science showcase........................................................................16
The UK’s wet summer, the jet stream and climate change ................................................21
Record low for Arctic sea ice extent ..................................................................................22
Hurricane Sandy and the value of ensemble forecasting ..................................................23
2012 hurricane season comes to an end ..........................................................................24
Extreme rainfall in the UK .................................................................................................25
Concluding remarks ...........................................................................................................26
ANNEX – UK Monthly Summary ........................................................................................27
ANNEX - The year’s major events in brief ........................................................................28
ANNEX – the 2012 UK climate summary...........................................................................31
1
Introduction
The UK’s weather in 2012 could be characterised as a year of two seasons – the dry,
followed by the wet. Once again, the great variability in the UK’s weather has emphasised
the importance of skilful, comprehensive predictions of our weather and climate for effective
decision making, mitigation of risks and realisation of opportunities. And again, events during
2012 highlighted the considerable direct and indirect impacts that our weather has on us –
our livelihoods, property, well-being and prosperity.
This paper provides an overview commentary on our weather during the past year. It is not
intended to be a comprehensive assessment (though many analyses of this year’s conditions
and the ongoing science developments are routinely published in peer-reviewed literature
and elsewhere). Rather, it aims to give a few representative snapshots of the Met Office’s
successes and challenges in providing the best possible advice and guidance to users
across all sectors. A number of case studies illustrate applications of the ongoing long-term
research and development, and its implications for improved accuracy and confidence in our
predictions.
2
UK climate overview
Provisional figures for the UK’s climate during 2012 (Figure 1) show a particularly
unremarkable year in terms of average temperatures, in contrast to a particularly remarkable
year of rainfall patterns. Overall, 2012 was the second wettest year in the UK national record
dating back to 1910, and just a few millimetres short of the record set in 2000. Exceptionally
wet conditions occurred across many parts of England, and especially in north east England.
2012 was the wettest year on record for England and third wettest for Wales. Only in north
and western areas of Scotland and west Northern Ireland were annual rainfall totals below
average (the 17th wettest annual total for Scotland and 40th wettest for Northern Ireland).
The annual climate averages mask the great variety and diversity of weather conditions that
we experience over the course of a year however. Further details of this variability and the
most notable weather are provided in the Annexes. Overall, 2012 might be characterised as
a ‘year of two seasons’. The first three months (January to March inclusive) were notably dry
(and generally warmer than average), continuing the recent run of dry winters and leading to
drought concern in England. In stark contrast, the remainder of the year has been
remarkably wet (and generally cooler than average). There have been numerous incidences
of flooding and storm damage, with the some regions being affected by a number of severe
events through the year. April and June were exceptionally wet.
Figure 1: Provisional annual mean temperature and rainfall maps for 2012, shown relative to
the long-term 1981-2010 mean climate.
In what has been an exceptionally wet year Met Office forecasts have risen to the
challenge with rainfall forecasts correct 72% of the time, well above the target of 60%
(note it is difficult to forecast rainfall at a pinpoint location, therefore the target for this
element is not as high as for others as currently defined. For example, one location may
have rain and a location a mile away may remain dry). The importance of accurate
forecasting has also been very apparent. Surveys have shown that 76% of the public think
our forecasts are accurate and 90% find them useful in helping them plan, prepare and
protect themselves from the weather.
3
Overview of the global climate in 2012
2012 was characterised by extreme weather around the world, from the US drought to UK
floods. All are related to continued major perturbations in the global climate system driven by
a range of possible factors. The focus of this analysis will be April to December 2012 when
the UK experienced two record-breaking wet months (April and June) and one of the worst
summers on record.
The major La Nina that generated large and damaging variations in weather and climate
around the world during 2010 and 2011 terminated during 2012 to be replaced by a weak El
Nino. However this has been short-lived and the tropical Pacific Ocean is once more entering
a period of near-normal (neutral) conditions. On the other hand major anomalies in ocean
surface temperatures, particularly in the North Pacific and North Atlantic, have persisted
through 2012 (Figure 2, left panel) and are likely to have contributed to the major
displacements in the jet stream that have characterised the climate of 2012. Likewise Arctic
sea ice cover declined to a record low level in September 2012 and there is increasing
scientific evidence that this may affect the position of the jet stream over the North Atlantic.
Figure 2: Left: Global sea surface temperature anomalies (°C) for April to December 2012.
Right: Global anomalies of satellite-observed Outgoing Longwave Radiation (OLR). OLR acts
as a good proxy for rainfall with lower than normal values (blue to purple) indicating increased
rainfall and vice versa.
Despite El Nino/La Nina being in near neutral conditions, La Nina-like patterns in tropical
rainfall have continued to persist, with above normal rainfall across the Philippines and the
tropical West Pacific (Figure 2, right panel). Figure 2 also highlights the intense and
damaging drought over the US and the above normal rainfall over West Africa, accompanied
by serious flooding events, and over the Caribbean. The perturbations to the tropical heating
pattern seen in Figure 2 (right panel) have likely contributed to the large amplitude wave
patterns that have characterised the northern hemisphere circulation during 2012 (Figure 3).
The prolonged spell of wet weather over the UK lasting from April to December was
associated with a persistent trough over the UK with high pressure to the northwest, evident
in Figure 3. At the same time, the North Atlantic jet stream, which generates and guides the
weather systems that bring rainfall to the UK, has extended eastwards and been displaced
southwards compared to its climatological position (Figure 4). This has driven enhanced
cyclonic development to the south west of the UK and continued to reinforce the trough over
the UK.
4
Figure 3: Mean
circulation anomalies
for April – December
2012 based on upper
troposphere heights;
blue/purple shading
indicates upper
troughs and
yellow/red, upper level
ridges. Red dashed
arrows indicate
propagation of
planetary scale waves
potentially triggered by
anomalies in tropical
rainfall (i.e. heating).
Figure 4: Mean
upper tropospheric
winds for April –
December 2012
(upper panel) and
30-year average
climatology (lower
panel). Wind
direction is shown by
the arrows and wind
strength by the
colour shading.
5
The global context of this year’s extreme rainfall demonstrates the complexity of
understanding the influence of a range of possible drivers. As is often the case the Tropics
have likely played a role, but it is also probable that the extreme warmth of the north-west
Atlantic and the record loss of Arctic sea ice have also been instrumental in driving the jet
stream south of its normal position.
In addition to these factors, both the Atlantic Multi-decadal Oscillation (AMO: a pattern of low
frequency variability in North Atlantic Ocean temperatures) and the gradual warming of the
oceans due to climate change, may also have been instrumental in the heavy rainfall that the
UK has experienced this year. Figure 5 shows the evolution of global and North Atlantic sea
surface temperatures over the last 140 years, with the bottom panel showing the multidecadal variability once the global warming signal is removed.
Figure 5: Time series of the
global and North Atlantic sea
surface temperature
anomalies. The AMO index is
defined as the North Atlantic
sea surface temperature
anomalies with the global
warming trend removed.
Since 2000 the phase of the AMO has been such as to amplify the global warming trend so
that the North Atlantic is now significantly warmer than at any time in the 20 th century (Figure
5). Recent research by Sutton and Dong (Nature, 20121) has shown that the warm phase of
the AMO favours wetter summers and autumns over the UK with potential increases in
rainfall of over 10%. Coupled with the additional warming from climate change the
atmosphere over the North Atlantic is predisposed to carry more moisture potentially
resulting in heavier rainfall when it rains.
1
Sutton and Dong, (2012), Atlantic Ocean influence on a shift in European climate in the 1990s,
Nature Geoscience, 5, 788–792
6
Global warming in 2012
Preliminary analysis suggests that 2012 is on course to be the 9th warmest on record in
global mean temperature, according to the World Meteorological Organization (WMO). Using
information to October from three leading global temperature datasets, including HadCRUT4
compiled by the Met Office
and the University of East
Anglia, the WMO say the 2012
global average temperature is
14.45 °C. This is 0.45 ±0.10°C
above the 1961-1990 average.
Taking into account the range
of uncertainty in observing
global surface temperature,
scientists from the Met Office
suggest that 2012 is very likely
to be between the 4th and 14th
warmest year in a record
dating back to 1850. Final
figures for the whole of 2012
Global near-surface temperature in 2012 (Jan to Nov inclusive)
will be available in March
compared to the 1961-1990 average
2013.
The natural variability of our
climate is driven in large part by the El Niño Southern Oscillation (ENSO) in the tropical
Pacific Ocean. In the El Niño phase, global temperature tends to rise, whereas in the La Niña
phase it tends to fall. Due to a La Niña through the first part of the year, and its lingering
effects on global ocean temperatures, 2012 is shaping up to be cooler than the average for
the past decade.
The HadCRUT4 database,
published this year, includes upto-date data available from land
stations, new data from higherlatitude stations giving better
coverage of Arctic climate, and
improved and more extensive
sea surface temperature data.
It is important to understand how
short-term temperature trends such as those associated with La
Niña and El Niño - can
temporarily run counter to, or
augment, changes happening
over the longer term. The Met
Office Hadley Centre and
Global near-surface temperatures from 1850 to 2012 from Met
University of East Anglia
Office Hadley Centre/Climatic Research Unit HadCRUT4, NASA
GISS and NOAA NCDC
temperature series provides that
longer view, identifying the trend
that overlies short term variability. Although the first decade of the 21st century was the
warmest on record, warming has not been as rapid since 2000 as over the longer period
since the 1970s. These variations in global temperature trends are not unusual, with several
periods lasting a decade or more with little or no warming since the instrumental record
began. We are investigating why the temperature rise at the surface has slowed in recent
years, including how ocean heat content changes and how the effects of aerosols from
atmospheric pollution may have influenced global climate.
7
The ‘dry’ season
The dry start to the year continued a generally dry south/wet north pattern that occurred
during 2011. Figure 6 illustrates that average rainfall in 2011 saw record or near record low
amounts of rainfall in parts of the Midlands and East Anglia, while parts of Scotland had near
record amounts of rainfall.
Persistent rainfall deficits had accumulated over southern England over the preceding 3
years. The accumulated rainfall deficit for the period March 2010 to March 2012 was 384mm,
against the annual average rainfall for southern England of 782mm. Over this 2-year period
southern England therefore received only 75% of the long term average, making this the
driest such 2-year period, April to March, in the series from 1910. Parts of central England
have seen 6 consecutive seasons – from autumn 2010 through to winter 2011/12 – with
below average rainfall. This long term situation led to concern over water supplies,
particularly in central and eastern England, and the Environment Agency declared drought
conditions across several counties in spring 2012.
March 2012 was particularly dry - the 5th driest March across the UK in the series from 1910,
and the driest since 1953. Most of the UK received less than 50% of average and a broad
swathe from south-west England through to north-east Scotland, and Northern Ireland, less
than 33%. March was also a notably warm month – the third warmest on average for the UK.
Figure 6: a) Annual mean rainfall anomaly maps for 2011, shown relative to the long-term
1981-2010 mean climate. b) Rainfall anomalies during the 2011/12 ‘winter recharge’ season
between October 2011 and March 2012.
Briefing provided to Government in March 2012 assessed the climatological context of the
drought, and how it related to previous major UK droughts. Multi-decadal variability in the
sign of the North Atlantic Oscillation, which is linked to AMO – a strong determinant of winter
temperature and rainfall; La Nina forcing from the Pacific; solar variability associated with the
11-year solar cycle; and stratospheric influences, may all have potentially played a role in the
2010-2012 UK drought.
8
We also noted however that neither the development nor the severity of the current drought
is exceptional compared with historical events, and its climatological drivers had several
similarities with past droughts.
A number of these drivers continue to be investigated. The impact of declining Arctic sea ice
on our winter weather patterns for example, favour colder drier winters and this is an area for
urgent investigation. Similarly, the impact of higher temperatures across the UK, as a result
of global warming, on UK water availability, through its influence on evaporation and soil
moisture particularly in summer, needs further investigation. The Met Office is also confident
that implemented and planned increases in the horizontal and vertical resolution of the Met
Office Hadley Centre climate model should deliver more reliable monthly to seasonal
forecasts and more robust scenarios of future risks of prolonged dry spells under climate
change.
9
The January windstorm and the Hazard Impact Model
A major winter storm brought very strong winds across much of the UK on 3 January 2012.
The strongest winds were across Scotland’s central belt, gusting at well over 70 knots
(81 mph) – strong enough to cause some structural damage. Several stations in this area
recorded their highest gust speeds for 13 years. Transport services across Scotland were
disrupted. More than 100,000 homes and businesses were left without electricity and some
buildings were damaged. The Met Office issued a red alert for strong winds well in advance.
The Hazard Impact Model is currently under development to support the work of the Met
Office Hazard Centre and the Natural Hazards Partnership. The January windstorm has
been used as a test case. Wind gust and wind direction information from the Met Office’s
high resolution weather forecast model is combined with information from Birmingham
University overturning thresholds for particular vehicles. The weighted gust field is then
extracted to the road network. Road segment specific wind direction range thresholds are
also generated, and compared with the forecast wind direction. Additionally, segment specific
‘exposure’ information based on the number of vehicles using each road is considered.
UK wind gust speed forecast
for 1100 on 3 Jan 2011. White
indicates greatest gust
speeds, with black indicating
low gustiness.
Weighted wind gust, based on
vehicle overturning
thresholds, for 1100. White
indicates greatest vehicle
overturning hazard, with
black indicating lowest
vehicle overturning hazard.
Risk of disruption from
vehicles being overturned on
the major road networks in
the UK for 1100 on 3 Jan. Red
indicates greatest risk of
disruption from a vehicle
being overturned with yellow
through to green indicating
lower risks of disruption from
a vehicle being overturned.
All coloured dots show
potential impact.
Had the Hazard Impact Model been used operationally, additional guidance on the likely
impact of the weather warnings provided could have been provided. Although the Central
Belt of Scotland is identified at major risk, the dominance of the M1 and M25 on the national
scaling over-shadows the impacts that were felt in Scotland. One area for further study would
be whether independent scaling for Scotland and Wales would produce a more realistic
output. The M25, M6, A66 have also all been identified as high risk mirroring news reports of
high impacts, including vehicle overturns and bridge closures. The M1 and parts of the A1
have also been identified and this is likely associated with their orientation. A review of the
importance of direction needs to be completed to fully understand how this parameter relates
to the wind gust parameter in terms of its influence on vehicle overturning.
10
European cold weather and sudden stratospheric warming
The only significant cold weather during early 2012 occurred across central Europe in early
February, with several hundred cold weather related fatalities in Ukraine and Russia and
widespread low temperatures and snowfall. The cause of the cold conditions was the
development of a large ‘blocking’ anticyclone over Scandinavia and north-western Russia.
Easterly winds on the southern edge
of this system transported cold
continental air westwards, displacing
the more usual mild westerly
influence from the Atlantic Ocean all
the way to the British Isles. A
‘blocking anticyclone’ can be thought
of being like a very large boulder
stopping the flow of a stream. In this
instance a block stops the more
normal westerly flow that brings
milder conditions, allowing colder
Global land and sea surface temperature anomalies for 1-5
conditions to win out from the east.
February 2012
The origin and persistence of blocks
has been a subject of much research, but their inception is often likely to rely on the
intrinsically unsteady patterns of flow of the lower atmosphere spontaneously achieving a
blocked state. What we do know though is that the origins of the large blocked pattern across
Europe in February 2012 could be traced back to the appearance of two individual regions of
mid-latitude blocking over central Russia and the Bering Sea in mid January. Over the next
two weeks, these two regions merged together.
Despite the general unpredictability of blocking patterns, there were potential signs of an
increased risk of a significant cold weather as early as mid January when the high altitude
winds in the stratosphere began to weaken in longer-range forecasts, related to a ‘Sudden
Stratospheric Warming’ event. We understand that there is a clear link between the
weakening of these high altitude winds and the surface weather which operates on monthly
timescales. In situations like this it can provide a ‘window of opportunity’ for monthly
forecasts to warn of increased risk. Based on this understanding, the Met Office 16 to 30 day
forecast correctly reflected the increasing risk of cold conditions since mid January.
Met Office Hadley Centre
scientists have investigated
and demonstrated a clear
stratospheric influence on
surface climate during these
events, with easterly winds
burrowing down through the
atmosphere to affect the jet
stream and surface climate.
The result is a switch from
mild westerly Atlantic flow
over Europe to easterly
Weakening of the jet stream in the stratosphere can allow easterly
winds with an increased risk
winds to move down through the atmosphere to give cold easterly
winds at the surface. This can result in cold and snowy weather
of cold extremes.
across the UK.
A similar ‘Sudden
Stratospheric Warming’ situation occurred in February 2009 when there was significant
snowfall across the UK and other parts of Europe, following a strong breakdown of the high
altitude jet. Although only some cold winter spells can be predicted in this way, other recent
winters such as 2006 and 2010 have also shown clear examples of the effect.
11
‘Spot on’ snow forecast supported by latest Met Office science
In early February 2012, the Met Office’s highly accurate forecasts of heavy snow and
widespread ice enabled the country to prepare for the hazardous conditions helping to keep
the country moving. At Heathrow Airport, for
example, snow arrived within ten minutes of when
Met Office forecasters had predicted – giving vital
guidance for those managing the situation.
This level of forecasting accuracy is far from easy
to achieve, however. Snow is an example of a
small-scale weather feature, affected by a number
of variables and notoriously difficult to forecast, not
least because the difference between rain and
snow requires only a small change in temperature.
The Met Office is using cutting-edge developments to improve the accuracy of forecasts in
these challenging situations which deal with so-called ‘small scale’ weather. These include
intense rain showers or thunderstorms – which can be just a few hundred metres across - or
weather which depends on fine details of the land surface, such as snow or valley fog.
These types of weather can be very difficult to represent in forecasting models.
At the current global weather forecast resolution (using a grid-scale of 25km), large
scale weather patterns will be generally well reproduced but the model will be unable to
capture the detail of small scale weather. To tackle this, the Met Office has developed the
UKV model. This involves running a version of the model which focuses on the UK, allowing
a much smaller 1.5km scale to be used. Information is fed in to the edges of UKV from the
25km global model. The 1.5km grid-boxes enable UKV to capture things like snow much
better, leading to improved forecasts in many situations.
In most situations, even with a 1.5km grid, current science and technology does not enable
the prediction of the exact location and timing of each shower that passes over the UK.
However, the increased detail gives a better indication of the character of the weather and
could be useful for giving probabilistic forecasts – which give the chances of, for example,
rainfall in a given place at a given time.
The 1.5km weather model also helped with the accuracy of snow forecasts in the very cold
and snowy weather at the end of 2010. In November of that year, numerous heavy snowshowers were carried inland from the sea in a NE wind causing significant disruption in the
north east of England. The figure shows that for the coarser 12 km model (NAE) showers
stall over the coast
causing a major
underestimate of snow
inland. This is a well
known problem with
models of this grid length.
In contrast, the UKV is
able to represent the
showers more realistically
and brings the showers
inland, producing a much
better forecast. The UKV
better represents what
actually happened as
24 hour accumulations for 25 Nov 2010 from UKV and 12 km (NAE)
shown by the radar image
models compared to that actually observed by radar. This shows an
to the left.
example of the advantages of a high resolution models
12
The ‘wet’ season
The driest spring for over a century ended rather abruptly. April was the wettest April in the
UK series since 1910, and also the coolest April in over 20 years; more than double the longterm average fell across most of England and eastern Scotland. The cool, wet theme
continued until the last 10 days of May. The weather in June was also dominated by low
pressure, with an unrelenting succession of frontal low-pressure systems tending to stall over
or close the UK, associated with a southerly shift in the jet stream. Most of England, Wales,
southern Scotland and Northern Ireland received double the average amount of rain, making
it the wettest June since records began in 1910. The 3-month period April to June was the
wettest on record. According to the Environment Agency, this led to some river levels tripling
and reservoirs going from the lowest ever levels to full or exceptionally high. Flooding hit
almost every region of England and Wales.
Figure 7: UK monthly mean rainfall anomaly maps for a) April 2012 and b) June 2012, shown
relative to the long-term 1971-2000 mean climate.
This theme continued into July, with the track of the jet stream finally moving further north
around 21st July, with high pressure influencing the southern half of the UK, bringing several
days of warm and sunny weather toward the start of the Olympics. Overall, August was a
rather unremarkable month of weather – the best month of summer 2012!
Summer 2012 was the second wettest summer in the series from 1910 for the UK overall
with 371mm, significantly wetter than summer 2007 (358mm) with only the ‘calamitous’
summer of 1912 wetter (384mm). Four of the last 6 summers have been among the wettest
10 in this series - these being 2007, 2008, 2009 and 2012 - with the intervening summers of
2010 and 2011 'indifferent' at best. The drier exception in summer 2012 was the far northwest of Scotland which received below average rainfall. The Met Office records also show
summer 2012 was overall cool and cloudy - it was the fourth dullest summer in the series
from 1929 and the dullest since 1987. Amounts were below average in June (70%), July
(81%) and August (95%). It was the second dullest June across the UK.
13
After some fine, settled weather in early September, there was a fairly typical mix of
autumnal weather through the season. Showers and rain were interspersed with shorter
settled periods - toward the end of the season these were typically cold with some frosts. The
north-east experienced some significant snow accumulations toward the end of October and
there were further snowfalls in the north toward the end of November. However, of most note
were several further periods of flooding. A vigorous area of low pressure affected a swathe
from south-west England, the west Midlands, north Wales and Northern England from 23rd
to 26th September. There was further flooding on 11th to 12th October - particularly across
eastern Scotland. 20th to 27th November was one of the wettest weeks of the last 50 years
as a succession of frontal systems brought heavy rain across England and Wales - more
than the monthly average fell widely within the week bringing flooding to over 1000
properties, several fatalities and widespread transport disruption.
This pattern continued into December, with further periods of exceptionally wet conditions
occurring during the second half of the month in particular. From 19th December through to
Christmas, a sequence of active depressions brought heavy rainfall and flooding to many
areas of the UK, with parts of south-west England again particularly badly affected.
14
Localised summer flooding and the UK ensemble
June’s rain led to a succession of flooding events across
the UK, including the south coast of England on 7-8 June,
Aberystywth on 8-9 June, West Sussex and Hampshire
on 10-11 June, Lancashire and West Yorkshire on 22
June. Torrential downpours from thunderstorms across
parts of central and northern England, with almost 30mm
of rain falling in 30 minutes in some places, resulted in
widespread flash-flooding on 28 June.
The flash
flooding in West
Wales led to a
major rescue.
The large-scale
detail of the rain
was well
represented in a
12km resolution
model (left), but
only the 1.5km
UKV model
(middle)
captured the
local severity.
Observed RADAR
1.5km resolution
weather forecast
12km resolution
weather forecast
Even the 1.5km resolution forecast is limited in that it produces a single representation of
what we know to be a very chaotic situation. As we understand from experience of largerscale weather forecasting and climate prediction, we need to run an ensemble of forecasts to
properly reflect the inherent uncertainty in the forecast – which may reflect on the exact
location, timing and intensity of a particular event. The Met Office achieved a landmark step
forward this year by trialling the first UK ensemble - a selection of 12 different forecast
realisations run at a 2.2km grid resolution.
Results from the Aberystwyth flood case (below) show
remarkable confidence in the prediction of significant
(>100mm) rainfall accumulations in the affected
Aberystwyth region. This capability has only just become
computationally affordable, following the installation of the
mid-life supercomputer upgrade this year, and is still a
research-mode system. When this capability is further
developed and tested to be implemented operationally,
forecasters will be better able to reflect the risk of severe
weather to users, enabling better mitigation of its impacts.
Probability of exceeding 32mm, 64mm and 100mm accumulations in a 24 hour period based on outputs
from the trial UK ensemble system. The observed radar accumulation above shows in excess of 128mm
15
Olympics 2012 and the science showcase
Our science and technology developments for the Olympic and Paralympic Games helped to
deliver increasing accuracy and detail in our weather forecasts during the Games, as well as
providing a basis from which future capability will be delivered. As part of the services
provided for London 2012, the Met Office installed additional weather observation
equipment and developed enhanced forecasting capability to support our staff. The science
developments include daily air quality forecasts, high resolution wind and wave modelling for
Weymouth and Portland, high resolution ensemble forecasting at 2 km for the whole of the
UK and additional weather observing technology at Olympic sites.
Daily air quality forecasts
Weather plays a significant role in determining air
quality and air quality forecasts were made available
for all 5000 UK forecast locations on the Met Office
website. During the Olympics, air quality forecasts
were also available in animated map format. These
forecasts are produced from a 12km resolution grid
configuration of the Met Office Unified Model with the
UKCA chemistry and aerosol scheme. In the event,
there were only two short periods of elevated air
quality index values during the Games. Research is
continuing, particularly to improve representation of
emissions in the model. Our long term plans are for
the next generation of coupled UK high resolution
forecast models to include sufficient chemistry and
aerosol to provide air quality forecasts and their
feedbacks on the weather.
Wind and wave modelling for Weymouth and
Portland
Currently, our models can generate atmospheric weather data for every 1.5 km over the
whole of the UK. However, due to the complexity of the winds around Weymouth
and Portland a showcase capability was used which gave nearly 20 times more detail than is
usually available. A 333m grid model in the atmosphere provided guidance on small-scale
wind structures and was coupled to a 250m grid configuration wave model to capture the
influence of Portland and inshore bathymetry on the wave field. This ensured the highest
detail possible for forecasts for wind and waves in the area during the Games. Feedback
from the Weymouth
teams was extremely
positive, noting
especially the useful
guidance that the model
provided on low wind
days. This groundbreaking showcase
capability illustrates the
future potential that
exists, given sufficient
computing capacity to
run similar
configurations in a more
operational setup for
specific coastal
applications and
sectors.
16
High resolution ensemble forecasts
The introduction of the 1.5km high resolution UK
weather forecast configuration in 2009 has
provided cutting edge capability to help improve
the accuracy of forecasting for ‘small-scale’
weather features like thundery showers. For the
Olympics, the Met Office took high-resolution
forecasting a step further by implementing the
first UK high-resolution ensemble - running
multiple forecasts at the same time. The highresolution ensembles were tested throughout the
Olympics, before being subject to further research
with a view that the facility could be introduced
operationally in the future, potentially leaving a
legacy that will benefit the UK well after the
Olympic and Paralympic Games are over.
The UK ensemble was initially implemented on a
2.2km grid, solely because of inadequate
supercomputing power to support an ensemble
with the 1.5km UK forecast model grid size. In
order to achieve a reasonable update frequency,
the ensemble size is also restricted to only 12
members, although post-processing is able to
provide products with 24 members.
Example high resolution ensemble forecast
showing chance that temperature will reach
20 °C
Example of probabilistic wind forecast for Eton Dorney rowing venue
Map products
showing the
probability of
exceeding certain
thresholds for
rain, high
temperatures and
wind were
developed, while
site-specific
forecasts for
Games venues
were also
provided. A
specialist product
showing
probabilities of
tailwinds and
crosswinds was
provided to advise
organisers of the
rowing events at
Eton Dorney.
Forecaster feedback from the ensemble output and products was very positive. The UK
ensemble showcase is seen as a pre-operational trial of capability that is expected to
become operational in 2013 – enabled by the planned mid-life upgrade to the current
supercomputer.
17
Nowcasting Demonstration Project (NDP)
The NDP demonstrated a first implementation of convective-scale numerical weather
prediction to nowcasting – forecasting over time periods of just a few hours ahead to produce
accurate and timely forecasts of hazardous weather such as thunderstorms. To date,
nowcasting systems have been based on extrapolation of radar-based rainfall observations,
blended with model output. However, it has been evident for many years, that these
nowcasting systems all have severe limitations in capturing storm development. As a result,
and following the extension of the UK model to convective scale, attention is shifting to its
application in nowcasting. This is a very demanding objective, requiring major advances in
data assimilation to achieve a close match between the numerical model and the observed
radar precipitation.
The NDP combines the 1.5km resolution
version of the Met Office Unified Model with
a 3km resolution system for assimilation of
high frequency UK observations (including
Doppler radar wind and rainfall
observations). Improved representation of
the evolution and development of new
weather and storm systems is achieved by
combining an accurate depiction of the
current weather with improved
representation of its evolution using the fluid
dynamical, microphysical and
thermodynamical equations used in forecast
models.
The forecast model needs information on
temperature, humidity, cloud, wind,
pressure and aerosols (for fog and
precipitation formation) but no one
observing system provides this information
over all time and space. Up to
now, operational forecast systems have
typically used hourly observations which
may take 1-2 hours to reach the Met Office.
The NDP requires sub-hourly data that
need to reach the Met Office within 5-15
minutes of the observation time so very fast
processing and communication links are
required.
Snapshot example of radar rainfall hourly
accumulation in June 2012 (top) and the
corresponding nowcast prediction (given 1 hour
ahead) from the demonstration NDP capability
Again, the NDP has been enabled by the installation of the mid-life supercomputer upgrade,
allowing faster production of more technically advanced forecasts and data assimilation.
Computational cost means that the forecast domain had to be restricted to southern UK only.
A comprehensive assessment of the summer trial is underway, with a view to develop the
capability in anticipation of operational implementation given sufficient supercomputing
resource at the next machine upgrade.
18
Why was 2012 so wet?
There are many factors which can impact the notoriously changeable weather in the UK, so
no single one on its own can be said to be fully responsible. However, it is possible to isolate
contributing factors and, in the case of the wet summer of 2012, one of those is the northern
hemisphere jet stream as already discussed. This is a narrow band of fast flowing westerly
winds (i.e. blowing from west to east) in the high atmosphere. This band moves around and
also changes its track, from a fairly straight line to something more closely resembling a
meandering river. Its position can, and does impact weather in the UK and other parts of the
northern hemisphere.
In both March and April we saw a ‘blocking pattern’ in the jet stream, where it meanders
north and south instead of making its more usual eastward progress. Despite this, March
was warm and dry while April was cool and wet. So what is caused the difference? It comes
down to the position of the blocking feature. In March, the meandering of the jet stream
caused it to pass to the north of the UK – anchoring high surface pressure over the UK. This
suppressed cloud, increased sunshine and temperatures, and prevented the usual rainbearing Atlantic weather systems from the west reaching us. Soon after the start of April,
however, the whole pattern moved westwards, so the peak of the northerly meander moved
over the North Atlantic Ocean. The UK, in contrast, found itself under the adjacent southerly
meander, with the jet stream passing to the south of the UK over France and Spain. This
atmospheric set-up remained established for much of the late spring and early summer,
bringing low surface pressure, cloud and rain to the UK. Because the flow is still blocked,
without a west-to-east jet stream to blow the weather system through, the low gets stuck over
the UK, resulting in high rainfall totals overall.
Briefing provided to Government in July assessed whether the extraordinary transition from
dry to wet was predictable at lead times beyond that of short-term weather forecasts (i.e.
several weeks to months ahead). Extended range forecasting for the UK, out to 3 months
ahead, will always be particularly challenging because of our position within the global
climate system. Longer range forecasts rely on the fact that certain processes, particularly in
the oceans, act on long timescales that can influence the state of the atmosphere in a
predictable way over a long period (in contrast to the strong influence of short-lived
atmospheric variability on determining the weather at a particular time a few days in the
future). Whereas weather patterns in the tropics are particularly dependent on these slow
variations, such as El Nino/La Nina, which are generally predictable months ahead, weather
in the UK is dominated by the atmospheric circulation over the North Atlantic which is highly
variable, and thus less predictable weeks and months ahead. For the UK, we do feel the
effects of changes in the Tropics, but we are far away from them. This means that subtle,
and sometimes small, shifts in atmospheric circulation patterns can make all the difference
between fine, dry conditions and unsettled, wet weather over the UK several weeks or
months into the future.
19
Figure 8: Timeseries showing South of England monthly rainfall records over past two
years compared to 1971-2000 average. The succession of dry months, particularly
through the important winter recharge period suddenly give way to the wettest April on
record (for both South of England and UK as a whole) with June, July and August also
wetter than average – giving wettest summer in 100 years (again, for South of England
and UK).
During March 2012 the La Nina event that had persisted from 2009 was finally waning in the
Pacific (as predicted by the seasonal forecast system), although many parts of the global
oceans and tropical weather patterns still retained characteristics associated with La Nina. In
the northern hemisphere the jet stream was very disturbed, resulting in a wave pattern of
high and low pressure regions. As already noted, the UK was positioned under a strong high
pressure region resulting in very dry and warm conditions. In April, the wave pattern
underwent a significant shift to bring the UK under the influence of strong low pressure, with
prevailing south-westerly flow and heavy rainfall. It is possible that the cause of this shift in
the northern hemisphere circulation may have been associated with a shift in tropical
weather patterns. In particular, a strong Madden Julian Oscillation (MJO) occurred in March
– a large-scale tropical phenomenon which leads to disturbed weather patterns over a
timescales of typically 30-60 days. The changes originating over the Indian Ocean may have
influenced our northern hemisphere weather regimes.
The initiation of an MJO event is, however, largely unpredictable, and remains one of the
great unsolved challenges of tropical meteorology. It is therefore very unlikely that this event,
and its influence on northern hemisphere weather patterns, could have been anticipated in
forecasts produced in early and mid-March. In contrast, nearer-term weather forecasts were
able to capture the change to wet conditions in the UK with increasing confidence as we
moved into April (once the shift in tropical conditions was observed).
Better understanding and representing the drivers of predictability in the global climate
system that influence our weather patterns continues to be a priority for Met Office research
in order to deliver improved advice and services on all timescales. This is a key component
of the new Met Office Hadley Centre Climate Programme funded by DECC and Defra.
20
The UK’s wet summer, the jet stream and climate change
2012 again illustrated how our weather in the UK is complex and determined by many
different factors, including the position of the jet stream - the narrow band of fast moving
winds which runs from west to east across the Atlantic high up in the atmosphere.
Why was the jet stream stuck so far south this summer?
The jet stream, like our weather, is subject to natural variability – that is the random nature of
our weather which means it is different from week, month or year to the next. We expect it to
move around and it has moved to the south of the UK in summertime many times before in
the past. It has, however, been particularly persistent in holding that position this year –
hence the prolonged unsettled weather. This could be due to natural variability – a bad run of
coincidence, if you will – but climate scientists at the Met Office and elsewhere are
conducting ongoing research to see if there are other factors at play. Changes in sea surface
temperatures due to natural cycles may be playing a part, but there is more research to be
done before anyone can establish how big a role they play. Research has also suggested
that reducing amounts of Arctic sea-ice could be affecting weather patterns, but more
research needs to be done to confirm this link.
What about elsewhere in the world?
Looking at the bigger picture, the
jet stream may have been having
an impact elsewhere in the
northern hemisphere. It became
stuck in a persistent pattern of
waves, with one of these ‘waves’
taking it to the south of the UK.
Meanders of the jet north and
south can be seen across the US,
the Atlantic and into Europe.
Upper level wind patterns in early July 2012, with the northern
While the wet weather in the UK
hemisphere jet stream marked with arrows. The wavy nature of
occurred under a southward
the jet stream was persistent throughout June. Figure created
meander of the jet stream, floods
by the University of Reading based on data from ECMWF.
in Russia near the Black Sea
appear to have been beneath the next trough to the east. The US heat waves persisted
beneath a northward meander and a ridge of high pressure.
Is climate change playing a role?
In the long term, most climate models project drier UK summers with only a small chance of
wetter summers – but it is possible there could be other influences of a changing climate
which could override that signal on shorter timescales. If low levels of Arctic sea ice were
found to be affecting the track of the jet stream, for example, this could be seen as linked to
the warming of our climate – but this is currently an unknown. The Met Office Hadley Centre,
working with climate research centres around the world, is making strides in determining how
the odds of extreme climate events have been influenced by climate change. However, it is
very difficult to do this type of analysis with such highly variable rainfall events, so it may take
some years before we could confirm how the odds of this summer’s wet weather happening
have been altered by greenhouse gases. We do know that warmer air can hold more
moisture. We have seen a global temperature increase of more than 0.7 deg C (since preindustrial times) and this has led to an increase of about 4-5% in atmospheric moisture. This
means that when we do get unusual weather patterns such as we’re seeing now, it’s likely
there will be more rainfall than the same patterns might have produced in the past. In short, it
seems when it does rain, it is heavier. Taking into account this effect, perhaps it’s not
surprising new records like those for this April and June are being set. In fact, we have
observed four record wettest months in the past four years. If wet months occurred randomly,
we would expect only one record to have been broken since 2006. For temperature, April
(2011), May (2008), July (2006), September (2006) are all recent warmest records. Again,
this is much more frequent than would be expected if temperatures were not rising.
21
Record low for Arctic sea ice extent
On 16th September, Arctic sea ice extent reached a new record low value since satellite data
records began in 1979. According to the National Snow and Ice Data Centre (NSIDC),
observations show there were 3.41 million square kilometres of sea ice on 16 September.
This record low is some 0.76 million square kilometres lower than the previous daily record
set in 2007.
Satellite records have
shown a long-term decline
in sea ice extent, at an
annual rate of over 4% per
decade. The seasonal
minimum (September) ice
extent has declined at the
faster rate of 11% per
decade, and this rate of
decline has accelerated in
the past 15 years. The last
six years now make up the
lowest six daily minimum
extents in the 32-year
record. This record
minimum is 3.29 square
kilometres below the 19792000 average and 50%
Daily sea ice extent averages for the decades 1980, 1990 and 2000
along with the 4 lowest years, including 2012 (data from NSIDC)
lower than the average in
the 1980s.
Understanding, monitoring and modelling sea ice cover is of interest to Met Office scientists
as it plays a key role in our weather and climate. Sea ice decline is also iconic of climate
change in the Arctic, while the presence of sea ice determines the accessibility of the Arctic
ocean and can also affect European and global climate. Sea ice cover seasonally insulates
the atmosphere from the ocean, preventing the exchange of heat and gases. Sea ice decline
has a feedback on the climate system - less sunlight is reflected back into space and so the
planet warms, causing more sea ice decline. Observing, understanding and ultimately
simulating these processes in weather and climate models is critical to developing more
accurate weather forecasts and longer term climate projections.
2012 melt season
Detailed analysis and experiments will be
required to determine the exact causes of the
record low extent this year. However, it is likely
that there are two underlying causes; the
ongoing thinning of the ice, which preconditions
the ice to the possibility of large summer losses,
and the strong storm over the central Arctic in
August. This is different to the record low of
2007 where one of the main causes of the
record low ice extent was a high pressure
dipole which persisted throughout the summer a synoptic situation which we saw in early June
this year and also during parts of the melt
season in 2010 and 2011.
22
MODIS image of summer storm across Arctic, 6
August 2012
Hurricane Sandy and the value of ensemble forecasting
As many as 60 million people across 12 US states were thought to be in the path of
Hurricane Sandy – the largest Atlantic hurricane on record. It has been estimated to be the
second costliest hurricane after Katrina, causing damage of around $65billion. Lloyds of
London alone expect to face insurance claims up to $2.5bn. There were an estimated 253
associated deaths (of which at least 122 were in the Caribbean).
Robust information on the storm track, in particular on the location at which it would strike
land, were critical in advising on the potential severity and impact of the storm. Sandy was
particularly devastating in its storm surge in New York because she took an unusual track –
with an abrupt turn to the north west (where most storms continue to recurve out to sea). The
storm surge, which occurred at high tide, pushed water to 4.23m at Battery Park, New York,
beating the previous record.
Ensemble predictions – consistent predictions of
risk based on running a number of forecast
simulations - provided very good guidance in
advance of Sandy, up to 9 days ahead of landfall.
The Met Office global ensemble forecast
products are used worldwide as a component of
tropical cyclone warning and advice, together
with information from other centres. While the
Met Office deterministic (single run) forecast
solution steered Sandy to the east, the ensemble
solutions gave a much better result, closer to the
observed track and indicating significant risk of
landfall around the highly populated urban areas
including New York. Consistent results were also
seen from other forecasting centres, adding
further confidence to the advice provided at the
time to emergency responders. Louis Uccellini, Director of the US National Center for
Environmental Prediction stated that "the major model guidance they (on the forecast desks)
used were the ensembles for their consistency and overall agreement, especially the
ensemble means from ALL the centers (NCEP, ECMWF, CMC, UKMET). Watching the
forecasters work with the ensembles is what gave me the confidence to deal with the media
and FEMA coordination about the nature of the development, the turn of the system, the
lateral extent of the circulation pattern, and the intensity 5,4,3 2, days ahead of the system. I
believe the consistency of the message was key
to making the impact that it did as I consistently
emphasized the unique and dangerous attributes
of the impending storm. I have to say, it was the
ensembles (specifically the ensemble means) that
got the forecasters on the right track and provided
the consistency needed to convince the
emergency management community and others
to pay attention and take action."
In addition, the Met Office ran a high resolution
(4km) local area configuration of the forecast
model (in research mode) to provide further
guidance. This relocatable capability was used
during a number of significant weather events
around the globe this year to support international
colleagues and humanitarian emergency
preparations, including Typhoon Bopha in the
Philippines.
23
2012 hurricane season comes to an end
This year saw another active season in the North Atlantic with 19 named storms, of which 10
became hurricanes. Both the number of named storms and hurricanes were well above the
1980–2010 averages of 12 and six respectively. However, only one of these (Michael)
became a major hurricane (classed as Category 3 or higher – note Sandy reached Category
2 at its peak), which is below the average of three. This is the third year in a row with 19
named storms, which is unprecedented in the historical records. Only one other season –
2005, which saw the devastating Hurricane Katrina – has experienced more named storms
(28) since reliable records began in 1944.
An unusual season
The season has also been notable for the
high number of relatively short-lived
storms, with seven of the nine tropical
storms lasting just two days or less. These
storms contribute towards a high storm
count, but relatively little towards the
Accumulated Cyclone Energy (ACE) index
- a measure of the combined strength and
duration of all named storms in the season.
This is unusual in the long term record, but
has been an increasing trend over recent
years. This can almost certainly be
attributed to improvements in monitoring however, with satellite developments enabling us to
observe developments over the North Atlantic in ever greater detail. This means that we are
now identifying storms that could previously have gone undetected.
Many storms - but not much power
Because such a high proportion of this season's storms were short-lived and weak, the ACE
index was only moderately above average at 127. The average is 104. Many seasons in the
historical record have had a much lower total tropical storm count, but much higher ACE
index, for example the 2004 season recorded only 14 named storms but an ACE index of
225 – nearly twice that seen in 2012.
The Met Office public forecast for the North Atlantic hurricane season, which was issued in
May, continued its run of providing good guidance on the ACE index - with this year's actual
total well within the predicted range. On the number of storms, the total of 19 this year was
outside of the forecast range. Chris Landsea, Science and Operations Officer at the National
Hurricane Center in Miami, said: "Because we are now better able identify weak, short-lived
tropical storms than we were just 15 to 20 years ago, a simple count of how many storms
occur in a season is perhaps not the most representative measure of how active a season
has been. Using ACE index or number of hurricanes would be a more stable measure, less
prone to changes in technology during the last 40-50 years."
Experimental forecasts run by the Met Office during the 2012 season show that there is skill
for forecasting the number of hurricanes. In May 2012 the Met Office predicted that the most
likely number of hurricanes to occur during June to November 2012 would be six, with a 70%
chance that the number would be in the range two to ten. In the event ten hurricanes
occurred.
Longer-term trends
Overall the relatively high level of Atlantic hurricane activity continues a trend which started in
1995, with most years since then being above-average. To assess long-term cycles in North
Atlantic hurricane activity the Met Office is trialling experimental forecasts for up to five years
ahead. While this research continues, the Met Office will continue to monitor the drivers of
tropical storm activity over the next few months as we prepare the first forecast for next
year's season, which will be issued in March 2013. The main public forecast will be released
in May 2013.
24
Extreme rainfall in the UK
For England and Wales, and south-west England and
south Wales, the 7-day period from 20-26 November
(and 19-25 November respectively) was provisionally
the second wettest week in the last 50 years, behind
only a spell from late October to early November 2000.
Recent preliminary analysis carried out following the
extraordinary rain this summer suggests that the
frequency of extreme rainfall events in the UK may
be increasing. Statistics from the Met Office
National Climate Information Centre, the UK’s
official climate record, show days of particularly
heavy rainfall – defined as a 1 in 100 day event –
have become more common since 1960. This
suggests the UK’s regional climate is mirroring an
observed global trend towards more frequent
extreme rainfall. While the findings of the analysis
are preliminary and need further research, they
indicate a potentially important trend. There is
evidence to say we are getting slightly more rain in total, but more importantly it may be
falling in more intense bursts – which can increase the risk of flooding, especially
surface water flooding.
The frequency of 99%ile rainfall (i.e. a heavy rainfall event which
we would expect to occur only 1 in 100 days according to UK
climate averages) in individual years in the UK. In some years
these events become more frequent (say 1 in 75 day events) or less frequent (1 in 125 day event s,
for example). This gives a view on the incidence of extreme rainfall events since 1960. Year to year
variations are associated with prevailing weather patterns (e.g. 2003 heat wave; 2000 floods)
The trend towards more extreme rainfall events is one we are seeing around the world,
in countries such as India and China, and now potentially here in the UK. Increasing
global temperatures may be one factor behind the increase in extreme rainfall around
the world. A warmer atmosphere can hold more moisture and we have seen an increase
of about 0.7C in global temperatures since pre-industrial times. From basic physics, this
would equate to about a 4% increase in moisture in the atmosphere which means there
is, quite literally, more water to come down as rain. Much more research is needed to
understand more about the causes and potential implications. It is essential we look at
how this may impact our rainfall patterns over the next decade and beyond, so we can
advise on the frequency of extreme weather in the future and the potential for more
surface and river flooding. This will help inform decision-making about the need for
future resilience both here in the UK and globally.
25
Concluding remarks
Through developing the science, investing in the underpinning technology, and providing
ever more effective advice and guidance, the Met Office continues to provide trusted and
valued warnings when it matters. Our warnings and advice ensure that the public,
communities and businesses can be protected and safeguarded, both now and in the future.
This year has again illustrated however that we cannot be complacent. Despite the progress
and benefits realised, every year lives are put in danger or tragically lost, businesses and
insurers suffer billions of pounds worth of losses, and emergency responders are given
insufficient information to tightly target their resources. And every year our policy makers
have to plan ahead for climate change with only limited guidance on UK impacts.
The Met Office’s long-term programme of research and development continues to push
ahead to improve this situation – ranging from work to identify and represent the large scale
drivers of the UK’s climate to improve monthly and longer-range forecast models, to
developments in our ability to forecast more accurately the risk of intense localised
downpours hours and days ahead.
Continued long-term investment, scientific progress and operational delivery and diligence
are required to unlock the benefits that our science and services can deliver. The Met Office
will remain at the forefront of this ambition again next year, and in the years to come, so that
the UK can be more confident that it is doing all it can to protect lives and livelihoods, deliver
national resilience, competitiveness and preparedness and enable wise choices for our
nation’s adaptation.
26
ANNEX – UK Monthly Summary
27
ANNEX - The year’s major events in brief
3 Jan
Strong winds across
the UK from major
winter storm
Winds gusted at well over 81 mph. Fallen
trees blocked roads and rail lines and
damaged power lines. Mainline rail services
across Scotland were suspended and major
road bridges closed. More than 100,000
Scottish homes and businesses were left
without electricity and some buildings were
damaged. A man was killed in Kent by a
falling tree, and a bus driver seriously
injured. A crewmember was killed as a
vessel in the English Channel was struck by
a large wave.
Low Temperatures
and Snowfalls
Snow over central and eastern parts of
England. The lowest temperature of the
spell so far occurred on 4 February with a
reading of -12.4 °C at South Newington
(Oxfordshire). Heathrow Airport had to
cancel many flights on 4th.
February - early
spring warmth
The highest temperature recorded was 18.7
°C at Coleshill, Warwickshire, made this the
warmest February day in the UK since
1998. A significant number of stations
recorded their highest February
temperature on record.
Record March
temperatures across
Scotland
Maximum temperatures were particularly
high, across northern England and
Scotland, exceeding 22°C in places. The
March record for Scotland was broken on
three consecutive days. Temperatures also
came close to record values across Wales
and Northern Ireland. In Scotland, there are
only three dates in the historical record 29th March 1968, 12 March 1957 and 23rd
March 1945 - where 22 °C was previously
exceeded.
23
May
Late May warmth
across Scotland
A new May record for Scotland. The
prolonged warmth in Highland Scotland
was unusual, and this particular spell was
the most significant prolonged warm spell to
have occurred in Scotland, in May, in
digitised data from 1959
7
June
Stormy conditions
from an unusually
deep low
The lowest pressure recorded was 980.6
hPa on 7th June at Milford Haven, west
Wales. This is the lowest pressure
recorded, in June, in south Wales and
south-west England, in digitised records
from c. 1960
8
June
Flooding from
persistent rain in
Aberystwyth area
More than 1000 people were evacuated
and 150 rescued, many from caravan parks
as they were inundated with flood-waters.
Dozens of homes in several villages were
flooded
3-6
Feb
23
Feb
24-28
March
28
10-11
June
Heavy rain in
southern England
West Sussex and Hampshire were worst
affected with more than 70mm of rain falling
in a 16 hour period. The June average for
this area is typically around 60mm. There
were flooding problems on a number of
main roads and several reports of flooded
homes.
22
June
Flooding from
persistent rain in
Lancashire and West
Yorkshire
Around 500 properties were flooded by both
surface water flooding and where rivers
burst their banks; Isle of Wight rock festival
deteriorated into a sea of mud due to the
wet weather creating soft ground conditions
Widespread
thunderstorms and
torrential downpours
in the Midlands,
northern England,
Northern Ireland and
Scotland.
A series of major storms brought flashflooding and disruption widely across parts
of central and northern England and
Northern Ireland. The thunderstorms were
associated with hot, humid air from a
'Spanish plume' ahead of frontal systems
pushing in from the west; - In Shropshire,
one man died after being swept away in a
stream; There was widespread flashflooding affecting roads (including the A1 in
Newcastle) as drainage systems were
overwhelmed by the intense rainfall. Cars
were abandoned as streets became awash
with water. Hundreds of properties across
England and Northern Ireland were
flooded.; The East Coast main line was
closed between Newcastle and Berwick
due to landslides. The West Coast main
line was also affected by a landslip near
Tebay in Cumbria. The West Highland line
was blocked near Tulloch Bridge as a
landslide derailed a freight train.; Over 40
schools were closed in the Newcastle,
Northumberland and County Durham;- In
north-east England, over 20,000 homes
were without power due to lightining and
flash flooding. In Northern Ireland, over
1000 homes lost power.; In Leicestershire,
golf-ball sized hailstones caused damage
and were large enough to damage cars and
greenhouses.
Heavy rain and
flooding in Devon,
Dorset and elsewhere
40 to 50mm falling in the 24-hours between
00Z 6th and 00Z 7th. While there were no
very large-scale flood incidents, there was
disruption to transport networks and reports
of a number of flooded properties in many
widespread locations across the Midlands,
parts of Wales and also southern Scotland.
The flooding was exacerbated by the wet
ground conditions from the exceptionally
wet weather through all of June and early
July. From Friday evening and through to
mid-day Saturday 7th the focus of the
heavy rainfall shifted to south-west
England. Between 18Z 6th to 12Z 7th, 40 to
50 mm fell across parts of south and east
Devon, representing around the July
average rainfall in only 18 hours, resulting
in further flash-flooding. Several
Environment-Agency rain-gauges in East
Devon recorded over 100mm of rainfall, or
more than twice the July average, in a 33hour period. T in the Park Music festival at
Kinross was affected by rain and mud.
Waterlogged car-parks also affected visitors
to the British Grand Prix at Silverstone on
the Northamptonshire / Buckinghamshire
28
June
6-7
July
29
border. In south-west Engand, the worst
affected areas included South Hams (south
Devon), and the Otter and Axe Valleys in
East Devon, where dozens of properties
were affected by flash-flooding
5 Aug
18-19
Aug
23-26
Sept
20-26
Nov
19-20
Dec
Widespread torrential
downpours
reports of flash-flooding in southern
Scotland, north-west and north-east
England, Wales and south-west England,
impacts reported were mainly been due to
the intensity of the rainfall, rather than the
overall totals. This would have
overwhelmed drainage systems, resulting in
surface water flooding
Highest temperatures
of the year in S.E.
England
A very warm and humid southerly feed of
air was affecting the south-east of England.
With strong insolation too, temperatures
rose strongly, and Saturday 18th August
gave the highest UK temperatures of this
year, widely exceeding 30 °C, the highest
recorded value being 32.4 °C at Cavendish
(Suffolk).
Autumn storm
Unusually deep vigorous low pressure
system affected the UK. This autumn storm
brought widespread heavy rain
accompanied by strong winds and resulted
in numerous impacts - including localised
flooding accompanied by winds which were
strong enough to bring down trees in some
areas (still in full leaf at this time of year).
Heavy rain and
widespread flooding
from a sequence of
low pressure systems
Prolonged heavy rain fell across much of
south-west England overnight 20/21
November 2012 from a front/wave
associated with an area of low pressure.
Around 40 to 50mm fell across a 12-hour
period - notably wet but not exceptional.
However, with the ground already
saturated, there were widespread flooding
problems, particularly to transport routes
with flooding of roads and landslips. The
Exeter to London Great Western railway
line was also closed. Most dramatically, a
bank of the Great Western canal collapsed
near Tiverton, draining the canal into the
surrounding land. The worst affected
counties included Devon, Somerset and
Gloucestershire. Some of the flooding
problems were likely to have been
exacerbated by autumn leaves and other
debris blocking drains, and there were also
more intense bursts within the overall
event. The rain was accompanied by some
strong winds, gusting at 40 to 50 Knots in
exposed locations along the south coast.
Widespread heavy
rain from Atlantic
fronts
A particularly wet spell of weather on 19-20
December 2012 as Atlantic fronts brought
prolonged heavy rain to much of the UK. In
the 48 hours from 09 GMT 19th to 09 GMT
21st December 2012, around 50mm of rain
fell across parts of Cornwall, Hampshire,
south Wales, northern England and eastern
Scotland. Although totals were not
exceptional, the rain fell on saturated
ground, resulting in further widespread
flooding problems - many affecting the road
network due to surface run-off from
surrounding land. Neither the rainfall totals
were as high or the flood impacts as severe
as those experienced during an earlier wet
spell in late November.
30
ANNEX – the 2012 UK climate summary
APRIL
MARCH
FEB
JAN
rd
th
Major winter storm affecting southern Scotland on 3 ; mildest January since 2008; 4 sunniest January
since 1929.
Max T
Min T
Max 24hr
Max wind gust
Max snow depth 8cm
rainfall
14.0 °C at
-10.5 °C at
102mph at
at Aviemore
th
Teignmouth (Devon) Aboyne
64.8 mm at
Blackford Hill
(Highland) on 20 ;
on 18th
(Aberdeenshire)
Kinlochewe
(Edinburgh) on
8cm at Copley
on 16th
(Highland) on
3rd
(County Durham) on
11/12th
24th
Very cold spell during first 12 days with sharp frosts and snowfalls, especially across England; UK mean
temperature varied from about 0.5 °C below normal across southern England to 2.0 °C above in
Northern Ireland and northern Scotland; in many eastern and southern counties of England and parts of
eastern Scotland only about a third of the normal amount fell; driest February over England since 1998.
th
Cold weather on 4 resulted in travel disruption overnight and into the 5th, notably cancellation and
delays to flights from Heathrow and lengthy delays to traffic on routes such as the M25 and M40. On the
9th, freezing rain fell across northern England causing treacherous conditions on roads and pavements.
About 100 road accidents were reported from Cumbria, and hospital A&E departments dealt with
hundreds of falls on icy pavements
Max T
Min T
Max 24hr
Max wind gust
Max snow depth
rainfall
18.7 °C at Coleshill
-15.6 °C at
74mph on Fair
16cm at Malham Tarn
(Warwickshire) on
Holbeach
70.6 mm at
Isle on 24th
(North Yorkshire) and
23rd
(Lincolnshire) on Achnagart
Buntingford
11th
(Highland) on
(Hertfordshire) on 5th
17/18th
rd
3 warmest March in a series since 1910, warmest March since 1957; most of Wales, Northern Ireland,
south-west England, parts of northern England and eastern Scotland had less than a third of their normal
th
rainfall amount; driest UK March since 1952 and 5 driest since 1910; sunniest March in England since
1929;
Drought conditions persisted across East Anglia, the Midlands and southern England with continuing
concerns for farming, water resources and the environment generally. Late in the month, the area
officially in drought was extended to include parts of Yorkshire. The sustained dry weather and the
warmth of the last week resulted in wildfires in various areas including south Wales, Surrey and the
Scottish Borders.
Max T
Min T
Max 24hr
Max wind gust
Max snow depth
rainfall
23.6 °C at Aboyne
-8.5 °C at
71 mph at
4cm at Leadhills
(Aberdeenshire) on
Braemar
101.2 mm at
Blackford Hill
(Lanakshire) on 4th
27th
(Aberdeenshire)
Alltdearg House, (Edinburgh) on
and 5th
on 18th
(Isle of Skye) on 7th
6/7th
Generally unsettled with numerous showery days; coldest April since 1989; unusually, April was colder
than March (this last occurred in 1998) and the temperature failed to reach 20 °C anywhere (this last
occurred in April 1989); wettest April on record across the UK with much of eastern and southern
England, east Wales and eastern Scotland recorded well over twice the normal amount, with three times
normal in places.
About 10,000 homes in North-east England without power on 4th after ice and strong winds brought
down power lines. In the Cairngorms, nine hill walkers had to be rescued in heavy snow. Heavy rain and
strong winds across southern Britain on 25th brought localised flooding. Further heavy downpours across
northern England and Wales on 26th, led to flooding of homes and businesses in York. A stormy end to
the month led to hundreds of trees being uprooted, blocking roads and damaging power lines to leave
some 12,000 properties without power across southern UK. Despite numerous wet days, reservoir and
groundwater levels remained very low across much of England with continuing concerns for farming,
water resources and the environment generally. The area officially in drought was extended to counties
across the West Midlands and South-west England.
Max T
Min T
Max 24hr
Max wind gust
Max snow depth
rainfall
19.7 °C at Kew
-8.2 °C at
76 mph at
22 cm at Whitehillocks
Gardens (Greater
Braemar
46.0 mm at
Warcop Range
(Angus) on 3rd
31
JULY
JUNE
MAY
London) on 30th
(Aberdeenshire)
on 5th
Liscombe
(Cumbria) on
(Somerset) on
29th
29/30th
Dominated by cool and unsettled conditions, continuing the wet theme of much of April, though a marked
improvement occurred from 21st, with a much warmer and more settled spell; particularly warm across
Highland Scotland, and a new May temperature record for Scotland was set on 25th; third sunniest May
on record;
Badminton Horse Trials in Gloucestershire were cancelled because of waterlogged ground. Overnight
rain on the 2nd/3rd caused localised flooding across parts of Essex and Suffolk, with a section of the A12
closed for a time and a landslip causing train delays and cancellations between London and parts of East
Anglia. On 11th, the wet April and unsettled start to May allowed the lifting of drought orders. The last 10
days saw a run of very warm sunny days giving a welcome boost to tourism and outdoor activities
including the Olympic torch relay across western England and Wales.
Max T
Min T
Max 24hr
Max wind gust
rainfall
29.3 °C at
−6.2 °C at
67 mph at
Achnagart
Saughall (East
101.0 mm at
Blackford Hill,
(Highland) on 25th,
Ayrshire) on 5th
Kinlochewe
Edinburgh on
a new May record
(Highland) on
13th
for Scotland
13/14th
Dominated by low pressure over or close to the UK, with associated weather fronts; almost complete
absence of warm, settled spells; coolest June since 1991; wettest June across the UK in the series from
1910; equal-wettest June in the England and Wales series from 1766 (shared with June 1860). Only the
far north-west of Scotland was drier than normal;
Unsettled weather of the first few days affected some of the Diamond Jubilee celebrations, including the
rd
Thames pageant on the 3 . Dozens of uprooted trees brought down power cables and engineers worked
to restore power to nearly 300 homes across SW England on 7th. Persistent heavy rainfall across midWales during the 8th and into the 9th resulted in significant flooding in the Aberystwyth area. More than
1000 people were evacuated and 150 rescued. Further prolonged heavy rainfall across south-east and
central southern England on 11th resulted in localised flooding. Worst affected was West Sussex where
the flooding continued into the 12th affecting roads, caravan parks and hundreds of properties in the
Chichester and Bognor Regis areas. Rainfall on the 21st caused waterlogged ground at the Isle of Wight
rock music festival and resulted in traffic chaos for motorists arriving on the island, many spending the
night 21st/22nd in their cars. Persistent, and often heavy, rainfall for much of 22nd caused significant
flooding across parts of Lancashire, Cumbria and West Yorkshire with around 500 properties affected by
both surface water flooding and where rivers burst their banks. On 27th, torrential rain resulted in more
than 700 flood-related call-outs in Belfast and County Antrim. At the height of the flooding, many roads
were impassable and about 1,000 homes were left without power. Widespread and serious flooding
occurred following thunderstorms and torrential rain on the 28th affecting the Midlands, NE England and
parts of Northern Ireland and southern Scotland. As well as the flooding of properties and roads,
thousands of homes were without power and both rail routes between England and Scotland were cut.
Worst affected was NE England, where hundreds of homes were flooded, some 23,000 properties lost
power after sub-stations flooded, traffic gridlock occurred in Tyneside as roads flooded and a landslide
near Berwick closed the East Coast main railway line. Elsewhere, large hailstones damaged vehicles
and greenhouses in Leicestershire and a man drowned in floodwater in Shropshire. However, the very
wet weather continued to improve river, groundwater and reservoir levels. On 14th, Anglian Water,
Southern Water and Thames Water announced an end to the water use restrictions that they had
introduced in April.
Max T
Min T
Max 24hr
Max wind gust
rainfall
28.6 °C at
3.5 °C at Loch
82 mph at
Gravesend (Kent)
Glascarnoch
93.8 mm at
Needles Old
on 28th
(Highland) on
Blencathra
Battery (Isle of
th
5th
(Cumbria) on
Wight) on 8
22/23rd
Again characterized by low pressure, bringing rather cool, cloudy conditions and some high rainfall totals
in the first half of the month; coolest July since 2000; many parts of England, North Wales and eastern
Scotland having over twice their average rainfall;
Prolonged heavy rainfall across south and east Devon and Dorset resulted in rivers bursting their banks
with roads and dozens of properties flooded. The A35 trunk road and the Exeter to Yeovil rail line were
32
AUGUST
SEPTEMBER
OCTOBER
closed for several days. On the 9th, the Calder valley in West Yorkshire was hit by flash flooding after
heavy rain, affecting roads and properties in towns such as Hebden Bridge for the third time in about 2
weeks. Some weekend outdoor sports and music events such as the qualifying sessions for the Formula
One Grand Prix at Silverstone were adversely affected by waterlogged ground. The National Trust
reported that the persistently cool wet conditions had proved difficult for wildlife, particularly many insects
and birds. A much warmer, more settled interlude lasted a week from the 21st, especially over England
and Wales where it coincided with the start of the school summer holidays. This was welcomed in view of
the poor summer so far.
Max T
Min T
Max 24hr
Max wind gust
rainfall
30.7 °C at St
0.0 °C at
62 mph at
James’s Park
Resallach
74.9 mm at
Needles Old
nd
(London) on 25th
(Highland) on 2
Slapton (Devon) Battery (Isle of
on 6/7th
Wight) on 16th
Mainly influenced by low pressure over or to the west of the UK, bringing cloudy conditions and showers
or longer periods of rain on many days especially in the west and north. The south-east of England saw
the driest and warmest weather; a wet month in south-west England and south Wales and in northern
England, southern and eastern Scotland, with a few areas having over twice the average rainfall; in
contrast much of East Anglia and south-east England and parts of north-west Scotland and the west of
Northern Ireland were drier than normal
Olympic events in SE England in early August enjoyed largely fine, dry conditions. Prolonged heavy rain
in Cumbria on the 29th led to some localised flooding of properties and a landslip on a rail line in west
Cumbria. Reported that the generally wet and cloudy summer weather had adversely affected the yield
of many fruit, vegetable and cereal crops.
Max T
Min T
Max 24hr
Max wind gust
rainfall
32.4 °C at
-2.5 °C at
64 mph at South
Cavendish (Suffolk) Cromdale
64.2 mm of rain
Uist (Western
on 18th
(Highland) on
fell at Lerwick
Isles) on 27th
31st
(Shetland) on
21/22nd
First half was fine and reasonably warm, except in north-western areas, but the month became
progressively more unsettled and quite cool for all of the UK with a notably deep depression bringing
large amounts of rainfall and high winds to many areas from the 23rd to the 26th. The second half of the
month was cooler than the first, even relative to normal, with a few overnight frosts in the north; coolest
September since 1994; rainfall totals for the whole month were only close to average for many regions;
The Paralympics enjoyed generally fine weather. In contrast, an unusually vigorous area of low pressure
brought very unsettled weather to most parts from the 23rd to the 26th, giving particularly high rainfall
totals and some strong winds, resulting in some transport disruption, with localised flooding of roads, and
main rail routes closed for a time, properties in NE England were further affected by flooding and around
600 homes and businesses were reported to have been flooded across England and Wales since the
23rd.
Max T
Min T
Max 24hr
Max wind gust
rainfall
29.3 °C at Writtle
-4.1 °C at
72 mph at
(Essex) and
Braemar
97.8 mm of rain
Inverbervie
Cambridge on 9th
(Aberdeenshire)
fell at
(Kincardineshire)
on 23rd
Ravensworth
on 25th
(North
Yorkshire) on
24/25th
A typical autumnal mix of showers and rain for much of the time, but with a couple of short settled spells;
north east experienced some significant snow accumulations towards the end of the month mainly
across higher ground; coldest October since 2003; Northern Scotland had its 5th coldest October in a
series since 1910; rainfall and sunshine totals for the UK overall were close to their respective long-term
averages.
th
Intense downpours on 11 in parts of the south and west led to flash flooding in Clovelly (Devon) and
flooding was also reported across parts of west Wales. Prolonged heavy rainfall in north-east Scotland
th
on 12 with 50 to 70 mm recorded widely led to flooding of roads and disruption to rail services across
parts of Aberdeenshire, Angus and Fife, and the corner of one property in Fife was washed away by
th
floodwaters. Strong north-west winds combined with unusually high tides on 18 caused some coastal
33
NOVEMBER
DECEMBER
flooding in Devon and Cornwall. Widespread areas of fog across England and Wales affected transport
rd
on 22nd to 23 .
Max T
Min T
Max 24hr
Max wind gust
Max snow depth
rainfall
18.8 °C at Holbeach -7.8 °C at
78 mph at Needles 12 cm at Copley
(Lincolnshire) on 1st Braemar
70.4 mm at
Old Battery (Isle of
(County Durham) on
(Aberdeenshire)
Crombie
Wight) on 5th
27th
on 17th
Country Park
(Angus) on
12/13th
th
A showery and cool start, with frosts in some areas, led to milder conditions between 6th and 14 ; an
exceptionally wet spell from 19th to 26th brought widespread disruption from flooding and landslips with
some areas had up to twice the whole month’s normal rainfall amount within the space of a week; last
few days of the month were much colder, drier and brighter with some snow in the north; some places in
a band from Devon to Humberside had up to twice their normal amount of monthly rainfall, whereas
Northern Ireland and north-east Scotland were drier than average;
For England and Wales, the 7-day period from 20 to 26th November was one of the wettest weeks in the
last 50 years. The floods and storms led to several fatalities and there were widespread flooding
problems, particularly to transport routes with flooding of roads and landslips, and in total well over 1000
properties were flooded. Most dramatically, a bank of the Great Western canal collapsed near Tiverton,
draining the canal into the surrounding land. Many roads and rail services - including both main railway
lines from the south-west to London - were closed due to flooding and landslips. In Llanberis (Gwynedd)
around 100 homes were affected by flash-flooding. Further flooding affected Ulverston, Cumbria and
parts of Dumfies and Galashiels. By the 26th parts of Newcastle and a hospital in Northallerton were
affected by flooding. Across north-east England, further roads were closed and rail services affected including the East Coast main line near Darlington.
Max T
Min T
Max 24hr
Max wind gust
Max snow depth
rainfall
16.4 °C at Kew
-7.3 °C at
86 mph at Capel
2 cm at Warcop
Gardens (Greater
Braemar
88.4 mm at
Curig (Gwynedd)
Range (Cumbria) on
London) on 13th
(Aberdeenshire)
Holne (Devon)
on 22nd
26th, Albemarle
on 29th
on 24/25th
(Northumberland) on
27th and Shap
(Cumbria) on 30th
The first part of December brought unsettled and showery weather, with temperatures struggling to reach
seasonal normal values but no particularly notable heavy rainfall. Pressure built around 10th, and there
were then a few days of quiet anticyclonic weather, allowing the first really severe frosts of the season (12.5 °C recorded at Braemar on 13th). On 14th/15th an extensive low-pressure area brought fronts
across the UK, giving heavy rain across all districts, and bringing temperatures back to near the seasonal
average. During the second half of December, the UK was mainly under the influence of a large area of
low pressure in the north Atlantic. This brought a mainly westerly or south-westerly flow with very mild
but exceptionally wet conditions. From 19th December to Christmas, a sequence of active depressions
brought heavy rainfall and flooding to many areas of the UK, with parts of south-west England particularly
badly affected.
Max T
Min T
Max 24hr
Max wind gust
Max snow depth
rainfall
15.0 °C at
-12.9 °C at
79 mph at Capel
20 cm at Fettercairn
Westonzoyland
Braemar
89.4 mm at
Curig (Gwynedd)
(Kincardineshire) on
(Somerset) on 22nd (Aberdeenshire)
Tyndrum
on the 28th and
6th
on 6th
(Perthshire) on
Uist (Outer
20/21
Hebrides) on 29th
34
35
Met Office
FitzRoy Road, Exeter
Devon EX1 3PB
United Kingdom
Tel: 0870 900 0100
Fax: 0870 900 5050
[email protected]
www.metoffice.gov.uk

Met Office Weather Review 2012 - Northern Ireland Environment Link

Transcription

Similar documents

SWURVE PROJECT PARTNERS UK

Texas Fire Potential Update

Written Response Test

Insurance version 3 - WeatherBELL Analytics

WMO Task Force on Social and Economic Applications of Public

FUNDRAISING Money Return Document

Brochure - XP Solutions

MIAMI VICE: WATER SQUAD CROCKETT AND TUBBS, A.K.A. THE

useproductguide - AK Interactive