Review and Experimental Long Range Forecast for SW England. July 2019.

Published 19 July 2019.

GDPR statement: Please note that the author of this blog does not set cookies but the host “wordpress.com” sets multiple cookies which are outside of the authors control. You can view their cookie policy here. 

1. Influences.

Changes in sea temperature.

Due to the recent settled and at times very warm weather, sea temperatures around the UK (and in the Mediterranean) have strongly recovered being above normal in the latest data. Sea temperatures around Greenland and Alaska are notably above average.

Tropical Atlantic has continued to warm and is forecast to remain slightly warmer than average – see Met Office graphic below:

In the Pacific weak El-Nino conditions have become weak and may now become neutral or even slightly La Nina this Autumn – see CFSv2 and NMME multi model ensemble forecast below. This may impact on the number of Atlantic tropical storms which are reduced during El Nino years. The latest forecast from Tropical Storm Risk (University College London) call for near normal numbers of Atlantic storms but stress the uncertainty with regards El Nino changes.

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) has been in a negative phase since later April 2019 which for the summer period translates to a colder/wetter phase for the UK and June reflected the wetter type in many areas but with temperatures near normal or slightly above. In July this has also been the case in Scotland but not further south. Recent NAO forecasts suggest a (possibly temporary) change to a positive state with drier and warmer types more likely.

NAO background information see the Met Office NAO information.

Recent Climatology

Despite a colder first half of June the warmer period at the end of the month led to near normal mean temperatures for most parts of the SW. Up until the 18th of July it has been dry with only about 1% of typical July rainfall. Data from the main SYNOP station show above average sunshine but a mean temperature of 17 Celsius which is near average, despite some very warm days. Probably parts of the SW have had warmer than average values once all the data is available early in August.

Met Office mean temperature anomalies Autumn 2018, Winter, Spring and June 2019

Met Office rainfall anomalies Autumn 2018, Winter, Spring and June 2019

Because of the June rainfall 12 month totals to end of June are close to average although but temperature is above average as shown by the Copernicus graphic below.

River flows in June reflect the wet month although annualised rates are below average more details including ground water can be found  in the  June 2019 Hydrological summary PDF 

Soil moisture content was still below normal over parts of the SW at the end of June and the dry first half of July is not likely to have helped.

The reservoir levels in the SW of England (14th July) show 73% storage which is slightly close to a normal July level.

Looking ahead the experimental product from the Global Flood Awareness System (Version 2) suggests reduced flood risk for the SW over the next few months although local flash flooding would not be included in this.

Atmosphere: Predictions.

A:  1: Stratosphere

Stratosphere is in summer mode as shown by the ECMWF 50hPa chart for 1200UTC 18th July 2019.

A: 2: Upper Troposphere

CFSv2 200hPa monthly mean forecast height (contours) and anomaly (lower row) for the period August to November 2019 based on 7th July show above normal heights throughout and it is not until February that some below normal heights are indicated over the north of Scotland.

CFS2 200hPa mean and anomaly August to November

CFS2 200hPa mean and anomaly December 2019 to February 2020

B: Lower Troposphere:

A selection of August to October 2019 solutions in low resolution from WMO using July data. Three month season and individual months. Top row temperature anomaly and mid row precipitation anomaly.

White areas are area where the probabilities of below/normal/above are similar hence there is no overall signal for this period from the WMO super ensemble which includes DWD, CMC, BoM, Moscow, Seoul, (CPTEC missing data), UKMO, Washington, Pretoria, Tokyo, ECMWF, Beijing and Toulouse seasonal models.

WMO super ensemble August to October

The super ensemble has an indication for above normal temperature but no agreement in the precipitation detail.

Some examples from individual centres are shown below. Full list can be seen at the seasonal forecast page.

UKMO ensemble August to October

Washington NCEP WMO ensemble August to October

NMME multi model ensemble August to November

NMME multi model ensemble December 2019 to February 2020

There are a few models that suggest colder and wetter periods in the August to October period but not the majority.

A summary for SW England from all the models for August to October looks roughly:
Temperature: 70% above normal, 20% normal 0% below normal and 10% no signal.
Rainfall:  15% above normal, 30% normal, 20% below normal and 35% no signal.

No signal = similar probs for above/normal/below

Additional model graphics can be seen at the seasonal forecast summary

C: Recent results for (April to June 2019):

Some good pointers to temperature anomaly and cooler signal in some models but the overall above average forecast for the season was correct. Some good indications from some models for a wetter June in England and in May for Scotland but idea of drier end to season was not correct, although the very end of June was dry and warm.

Most precipitation forecasts were poor.

Comparison graphics can be seen at the verification page for April May June 2019

2. Forecast. SW England.

Remainder of Summer 2019  (August) 

August is likely to see near or above normal temperature. There are slightly more solutions in favour of a drier than average month than those for a wetter one but thunderstorm rain rates could lead to some very wet days in a few places.

Higher temperatures may lead to shorter periods of heavier rain but fewer wet days which has been a pattern in recent years.

August climate: 1981 to 2010 average daily mean temperature 16 or 17°C in many areas, a little cooler over the N coastal areas of Devon and Cornwall  to 16 or 17°C  and a few degrees cooler over the moor. Locally over 17C in parts of Somerset.  Average rain in August typically 60 to 80mm, but 40 to 60mm in places especially East of the moors and in Somerset. Locally over 100mm across the moors.

Autumn 2019  (September October November) limited data. 

Overall the season is likely to see above normal temperatures, possibly nearer normal in September and much milder later in Autumn.

Rainfall is likely to be below normal for the season, especially in the S and E of the region perhaps nearer normal elsewhere. Little agreement as to which month could be wetter but some hints that it could be October.

Autumn climate: 1981 to 2010 average mean temperature 11 or 12°C but nearer 10°C in rural areas. Maximum temperatures average 14 to 16°C. November normally colder than October which is colder than September. Average 1981 to 2010 rain 300 to 400mm, 600 to 800mm over the moors but east of the moors and in lowland Somerset more like 200 to 300mm. September often drier than October or November.

Winter 2019  (December January February) limited data. 

The indication for a milder than average winter remains the main signal. Rainfall is likely to be above average although there are hints that December and / or February may be less wet in parts of the S and E of the region. Below average snowfall more likely than above average.

Winter Climate: 1981-2010 average temperature values for lowland areas 7°C in the West and 5°C in the East. Rainfall; Dec and Jan typically wetter than February. 1981-2010 Autumn average 300-400 mm lowlands but 200-300 mm areas to E of Dartmoor. Snow climatology less than 5 days lying snow over lowland areas 5 to 10 hills, say hills around 200 metre elevation – one in three years have no lying snow.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary can be seen at  here.

The attempt at a Regional Forecast for SW England aims to test whether such a forecast of temperature and rainfall variation from average can be made using numerical model data available on the internet. The forecast should not be used for any other purpose. A brief verification summary for the UK and Eire is routinely published at http://www.weather-info.co.uk/wxsvc/Verification.html or Click here for the Teignmouth and Dawlish summary

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

NMME information:   http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-12-00050.1

CFS2  info

GLOFAS Acknowledgement: Data were provided by the Global Flood Awareness System – GloFAS (http://www.globalfloods.eu/) of the European Commission Joint Research Centre and the European Centre for Medium-Range Weather Forecasts.
Reference: Alfieri, L., Burek, P., Dutra, E., Krzeminski, B., Muraro, D., Thielen, J., and Pappenberger, F.: GloFAS – global ensemble streamflow forecasting and flood early warning, Hydrol. Earth Syst. Sci., 17, 1161-1175, doi:10.5194/hess-17-1161-2013, 2013.

‘Copernicus Products’  as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus  http://climate.copernicus.eu

International seasonal monthly data from WMO

Stratospheric Diagnostics from Japan Met Agency and Free University Berlin

Climate data from The Met Office UK and NCEP USA

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Review and Experimental Long Range Forecast for SW England. June 2019.

Published 18 June 2019.

GDPR statement: Please note that the author of this blog does not set cookies but the host “wordpress.com” sets multiple cookies which are outside of the authors control. You can view their cookie policy here. 

1. Influences.

Changes in sea temperature.

Due to the recent unsettled and rather cool weather the sea temperature around the UK (and western Mediterranean Sea) is mostly a little below the average along with much of the North Atlantic (40 to 55North).

Tropical Atlantic seems to be warming and is forecast to remain warmer than average – see Met Office graphic below:

In the Pacific weak El-Nino conditions have continued and are expected to persist as indicated by CFSv2 and NMME multi model ensemble forecast (shown below).

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) returned to slightly positive from mid April after the first negative phase period for some time but shortly after went and remained negative. For the summer period this translates to a colder/wetter phase for the UK.

NAO background information see the Met Office NAO information.

Recent Climatology

In the SW of England, June  has been wetter, colder and cloudier than average. Main station SYNOP data to the middle of June showed the average temperature anomaly to be around minus 1 C with rainfall between 20 and 50% above average and sunshine only a third of average. This represents a significant change from overall warmer and drier weather of the last six months. Seasonal models historically have been poor at picking out a change to colder types.

Winter and Spring temperatures have been above normal and rainfall mostly normal or below across SW England.

River flows were showing below normal values in the east of the SW Region although groundwater seems near normal in the May report. The wet weather in June is likely to lifted river levels somewhat.

Full details can be found in the  May 2019 Hydrological summary PDF 

The reservoir levels in the SW of England (16th June) show 80% storage which is slightly below the normal June level, but recovering.

The June experimental product from the Global Flood Awareness System (Version 2) was not available on the 18th.

Atmosphere predictions.

A:  1: Stratosphere 

Remains in summer mode as shown by the ECMWF 50hPa chart for 17th June 1200UTC.

A 2: Upper Troposphere

CFSv2 200hPa monthly mean forecast height (contours) and anomaly (lower row) for the period July to November 2019 based on 7th June data, show mostly above normal heights but perhaps imply a slightly enhanced jet in mid Atlantic during October and more especially in November though perhaps to west of Uk.

B: Lower Troposphere:

July to September 2019 solution in low resolution from WMO . JAS and individual months. Top row temperature anomaly, mid row precipitation anomaly and lower row PMSL anomaly.

White areas are area where the probabilities of below/normal/above are similar hence there is no overall signal for this period from the WMO super ensemble which includes DWD, CMC, BoM, Moscow, Seoul, CPTEC, UKMO, Washington, Pretoria, Tokyo, ECMWF, Beijing and Toulouse seasonal models.

WMO July to August

UKMO JAS and monthly anomalies

NASA June 2019 to Feb 2020 Temp and Rain anomaly

NMME July to November 2019 top row temperature lower row rain rate anomaly.

NMME December 2019 to Feb 2020 top row temperature lower row rain rate anomaly.

There are several models that suggest colder and wetter summer but not the majority.

A summary from all the models for July to September looks roughly:
Temperature: 50% above normal, 31% normal 19% below normal.
Rainfall:  50% above normal, 28% normal, 22% below normal.

Additional model graphics can be seen at the seasonal forecast summary

C: Recent results for the Spring (March to May 2019):

Most models forecast above normal temperatures but NCEP, CANSIPs and JMA captured the trend for a less mild May.
Precipitation: Good indication that March could be wetter and some idea that the season could be wetter in places but was incorrect about the south/SW. Signal for below normal in places was correct but as usual exact location was not predicted well.

Comparison graphics can be seen at the verification page for Spring 2019

2. Forecast. SW England.

Remainder of Summer 2019  (July August) 

A warmer than average summer for the season is still more likely than not despite a colder two thirds of June.

Overall the balance has shifted towards above normal rainfall for the season.Models remain mixed at which month could be drier or wetter. However some longer dry spells seem likely over the next two months.

Higher temperatures may lead to shorter periods of heavier rain but fewer wet days which has been a pattern in recent years.

Summer climate: 1981 to 2010 average daily mean temperature 14 or 15°C in many areas to 16 or 17°C in main urban areas also locally east of the moors and more widely in Somerset. Maximum temperatures average 19 to over 21°C in similar areas. July often warmer than August. Average 1981 to 2010 rain in July typically 60 to 80mm, but 40 to 60mm in places especially East of the moors and in Somerset. Locally over 100mm across the moors. August slightly small areas with the lower rain totals due to July often being drier than August..

Autumn 2019  (September October November) limited data. 

A warmer September, then milder than normal each month and for the season.  Still looks likely that the Autumn could start drier in September then end with a wetter November, hence overall average or below average rain for the season.

Autumn climate: 1981 to 2010 average mean temperature 11 or 12°C but nearer 10°C in rural areas. Maximum temperatures average 14 to 16°C. November normally colder than October which is colder than September. Average 1981 to 2010 rain 300 to 400mm, 600 to 800mm over the moors but east of the moors and in lowland Somerset more like 200 to 300mm. September often drier than October or November.

Winter 2019  (December January February) minimal data. 

Milder than average throughout. Near or above average rainfall for the season. Below average snowfall more likely than above average.

Winter Climate: 1981-2010 average temperature values for lowland areas 7°C in the West and 5°C in the East. Rainfall; Dec and Jan typically wetter than February. 1981-2010 Autumn average 300-400 mm lowlands but 200-300 mm areas to E of Dartmoor. Snow climatology less than 5 days lying snow over lowland areas 5 to 10 hills, say hills around 200 metre elevation – one in three years have no lying snow.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary can be seen at  here.

The attempt at a Regional Forecast for SW England aims to test whether such a forecast of temperature and rainfall variation from average can be made using numerical model data available on the internet. The forecast should not be used for any other purpose. A brief verification summary for the UK and Eire is routinely published at http://www.weather-info.co.uk/wxsvc/Verification.html or Click here for the Teignmouth and Dawlish summary

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

NMME information:   http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-12-00050.1

CFS2  info

GLOFAS Acknowledgement: Data were provided by the Global Flood Awareness System – GloFAS (http://www.globalfloods.eu/) of the European Commission Joint Research Centre and the European Centre for Medium-Range Weather Forecasts.
Reference: Alfieri, L., Burek, P., Dutra, E., Krzeminski, B., Muraro, D., Thielen, J., and Pappenberger, F.: GloFAS – global ensemble streamflow forecasting and flood early warning, Hydrol. Earth Syst. Sci., 17, 1161-1175, doi:10.5194/hess-17-1161-2013, 2013.

‘Copernicus Products’  as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus  http://climate.copernicus.eu

International seasonal monthly data from WMO

Stratospheric Diagnostics from Japan Met Agency and Free University Berlin

Climate data from The Met Office UK and NCEP USA

Review and Experimental Long Range Forecast for SW England. May 2019.

Published 21 May 2019.

GDPR statement: Please note that the author of this blog does not set cookies but the host “wordpress.com” sets multiple cookies which are outside of the authors control. You can view their cookie policy here. 

1. Influences.

Changes in sea temperature.

Despite sea temperatures around the UK being above average.,much of the northern Atlantic is somewhat below average as is parts of the Mediterranean.

UKMO tropical N Atlantic forecast sea temperature

The forecast Atlantic tropical sea temperature (shown above) continues to suggest a warming trend although this has been reluctant to occur.

In the Pacific weak El-Nino conditions continue, see CFS2 and NMME multi model ensemble forecast below. Current forecasts are mostly slightly less warm, a more marginal El-Nino.

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) continued a negative phase which in summer would suggest colder / wetter condition for the UK. There is roughly a balance of models suggesting wetter verses drier but the majority suggest warmer.

NAO background information see the Met Office NAO information.

Recent Climatology

In the SW of England, main station SYNOP data to May 1800 20th shows the average temperature anomaly to be around -1 C with below average rain and near average sunshine hours.

Winter and Spring temperature until recently though have been above normal and rainfall for the last 12 months mostly normal or below.

River flows are again showing below normal values in the east of the SW Region although groundwater seems near normal in the April report.

Full details can be found in the  April 2019 Hydrological summary PDF 

The reservoir levels in the SW of England (12th May) show 86% storage which is slightly below the normal May level.

The experimental product from the Global Flood Awareness System (Version 2) based on early May ECMWF seasonal forecast for May to August 2019. The system does not suggest an enhanced flood risk for SW England.

Atmosphere predictions.

A:  1: Stratosphere 

The stratospheric has reverted to “summer” mode as shown by the ECMWF 30 and 10hPa images below for 1200UTC on the 18th..

A 2: Upper Troposphere

CFSv2 200hPa monthly mean forecast height (contours) and anomaly (lower row).

Generally above normal heights are forecast by CFS2 system for the summer months.

 

B: Lower Troposphere:

June to August 2019 solutions in low resolution from WMO . JJA and individual months. Top row temperature anomaly and lower row precipitation anomaly. Above normal orange/reds below normal in blue shades.

WMO multi model ensemble probabilities JJA

UKMO ensemble probabilities JJA

ECMWF JJA probabilities

NMME JJA 

CFS2 JJA (E3 data)

For the summer; Data from Australia BoM, Brazil, South Africa and Russia suggest below normal summer temperatures but the vast majority of solutions suggest above normal values for the season and each month. Rainfall solutions are more evenly balanced between the wetter and drier solutions.

For the Autumn.

Autumn NMME data

Autumn CFS2 E3 data

C: Recent results for the period February March and April:

Continuing on from recent reviews temperature forecast were fairly good but rainfall forecast were generally poor. Verification page for February to April 2019

2. Forecast. SW England.

Summer 2019  (June July August) 

A better than average summer is more likely than a less good summer.

A warmer than average summer for the season is likely and probably each month is likely to be above normal too.

Models are mixed at which month could be drier or wetter. Howver some longer dry spells seem likely. Overall near normal rainfall seems likely but uncertain as to whether it is the number of dry days or the rain total that will be lower/higher. Higher temperatures may lead to shorter periods of heavier rain but fewer wet days which has been a pattern in recent years.

Summer climate: 1981 to 2010 average daily mean temperature 14 or 15°C in many areas to 16 or 17°C in main urban areas also locally east of the moors and more widely in Somerset. Maximum temperatures average 19 to over 21°C in similar areas. July often warmer than August. Average 1981 to 2010 rain 300mm over the moors, typically 200 to 250mm in many coastal and eastern areas. June often drier than July and July drier than August.

Autumn 2019  (September October November) limited data. 

A warmer September then milder than normal, monthly and for the season.  Still looks likely that the Autumn could start drier in September then end with a wetter November, hence overall average rain for the season is possible.

Autumn climate: 1981 to 2010 average mean temperature 11 or 12°C but nearer 10°C in rural areas. Maximum temperatures average 14 to 16°C. November normally colder than October which is colder than September. Average 1981 to 2010 rain 300 to 400mm, 600 to 800mm over the moors but east of the moors and in lowland Somerset more like 200 to 300mm. September often drier than October or November.

Winter 2019  (December January February) minimal data. 

Milder than average throughout. Wetter start to winter then ending below average in February. Below average snowfall.

Winter Climate: 1981-2010 average temperature values for lowland areas 7°C in the West and 5°C in the East. Rainfall; Dec and Jan typically wetter than February. 1981-2010 Autumn average 300-400 mm lowlands but 200-300 mm areas to E of Dartmoor. Snow climatology less than 5 days lying snow over lowland areas 5 to 10 hills, say hills around 200 metre elevation – one in three years have no lying snow.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary can be seen at  here.

The attempt at a Regional Forecast for SW England aims to test whether such a forecast of temperature and rainfall variation from average can be made using numerical model data available on the internet. The forecast should not be used for any other purpose. A brief verification summary for the UK and Eire is routinely published at http://www.weather-info.co.uk/wxsvc/Verification.html or Click here for the Teignmouth and Dawlish summary

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

NMME information:   http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-12-00050.1

CFS2  info

GLOFAS Acknowledgement: Data were provided by the Global Flood Awareness System – GloFAS (http://www.globalfloods.eu/) of the European Commission Joint Research Centre and the European Centre for Medium-Range Weather Forecasts.
Reference: Alfieri, L., Burek, P., Dutra, E., Krzeminski, B., Muraro, D., Thielen, J., and Pappenberger, F.: GloFAS – global ensemble streamflow forecasting and flood early warning, Hydrol. Earth Syst. Sci., 17, 1161-1175, doi:10.5194/hess-17-1161-2013, 2013.

‘Copernicus Products’  as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus  http://climate.copernicus.eu

International seasonal monthly data from WMO

Stratospheric Diagnostics from Japan Met Agency and Free University Berlin

Climate data from The Met Office UK and NCEP USA

Review and Experimental Long Range Forecast for SW England. April 2019.

Published 21 April 2019.

GDPR statement: Please note that the author of this blog does not set cookies but the host “wordpress.com” sets multiple cookies which are outside of the authors control. You can view their cookie policy here. 

1. Influences.

Changes in sea temperature.

The sea temperature around the UK and across much of the North Atlantic is similar to last month being fairly close to the seasonal normal or a shade warmer/cooler in places.

The Met Office diagnostic for the tropical Atlantic (shown below) was near normal with a trend to above normal values in the majority of the ensemble solutions.

In the Pacific weak El-Nino conditions have continued, see CFS2 and  multi model ensemble forecast below but current forecasts are mostly slightly less warm.

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) returned to slightly positive (warmer wetter phase for UK) from mid April after the first negative phase period for some time.

NAO background information see the Met Office NAO information.

Recent Climatology

In the SW of England, main station SYNOP data to April 1800 20th shows the average temperature anomaly to be around +0.7 C, but zero in the east. Rainfall between 60 and 90% of average with about 55% of normal sunshine hours.

The mean temperature over the last six months has been above average except for January (which was near average). February was exceptionally mild and followed on from a warmer than average summer 2018.

Rainfall was above average in SW England during March (mainly until 17th). For the six month period October to March south parts were slightly above average but northern parts remained below the long term 1981-2010 average.

The recent wetter periods helped river flow recover from the lows in January but river flows were reported as slightly below average. Ground water in the east of the region remains normal but eastern parts of the UK have less good water resource levels.

Full details can be found in the  March 2019 Hydrological summary PDF 

The reservoir levels in the SW of England (14th April) show 88% storage which is slightly below the normal April level.

The experimental product from the Global Flood Awareness System (Version 2) based on early April ECMWF seasonal forecast for April to July 2019. The system does not suggest an enhanced flood risk for SW England.

Atmosphere predictions.

A:  1: Stratosphere 

The stratospheric polar vortex re-established and became unusually strong. Much colder than normal temperatures were recorded, especially at 10 and 30hPa.

Temperatures have recovered and it looks like the polar vortex will transition to “summer” mode by early or mid May as seen by the ECMWF forecast (dated 18th April) and shown below.

A 2: Upper Troposphere

CFSv2 200hPa monthly mean forecast height (contours) and anomaly (lower row).

Some indication of more troughing just west of the UK but overall weaker than normal jet flow may be lead to more blocked patterns. Uncertain location of higher pressure which may be further east for periods.

B: Lower Troposphere:

Selection of May to July 2019 solutions in low resolution from WMO (not all data available at date of issue) . Top row temperature anomaly and lower row precipitation anomaly. Above normal orange/reds below normal in blue shades.

Three month average anomalies sourced from WMO up to 20 April 2019

Above normal temperatures are indicated but data from Australia and Russia are the exception with a below normal temperature forecast. Rainfall patterns less clear cut with the cooler wetter output (2) slightly outnumbered by the near normal/uncertain (6) and drier solutions (3).

CFS2 (E3 data) 1st April for May to August

CFS2 (E3 data) 124th April May to August

Although temperature forecasts from CFS2 (E3 data) show consistent positive anomalies the rainfall anomalies are in less good agreement between model runs.

NMME data 9th April for May to August

C: Recent results for the period January February March:

Temperature mostly fair indication (scale no indication poor fair good). Signal for the milder February was confused by the colder indication due to a sudden stratospheric warming which although blocked patterns developed the flow remained mild rather than colder easterly.

Rainfall was fair at best and many models were poor. Month to month forecasts were poor. Pressure was slightly above average so at best only a partial signal. Better models seemed to be NMME and Japan.

2. Forecast. SW England.

Remainder of Spring 2019  ( May) 

Milder/warmer than average temperature is forecast by most models May in the SW of England.

Rainfall forecasts suggest than May could be drier than average (few models suggest wetter).

Spring climate: 1981-2010 average mean temperature 9 or 10°C but a few degrees cooler over the moors. Roughly  May 11 or 12°C. Average spring 1981 to 2010 rain 200 to 300mm lowest values in E Devon and over parts of Somerset. May roughly 80-150mm over the moors, 60-80mm elsewhere but 40-60mm locally to the East of Dartmoor and over large parts of Somerset and Dorset.

Summer 2019  (June July August) 

A better than average summer is more likely than a less good summer.

Warmer than average summer although temperatures in August may be closer to normal.

Models are mixed at which month could be drier or wetter. Overall near normal rainfall seems likely but uncertain as to whether it is the number of dry days or the rain total that will be lower/higher. Higher temperatures may lead to shorter periods of heavier rain but fewer wet days which has been a pattern in recent years. Indications of some linger dry spells.

Summer climate: 1981 to 2010 average daily mean temperature 14 or 15°C in many areas to 16 or 17°C in main urban areas also locally east of the moors and more widely in Somerset. Maximum temperatures average 19 to over 21°C in similar areas. July often warmer than August. Average 1981 to 2010 rain 300mm over the moors, typically 200 to 250mm in many coastal and eastern areas. June often drier than July and July drier than August.

Autumn 2019  (September October November) limited data. 

Warmer September then milder than normal, monthly and for the season.  Could start drier in September then  end with a wetter November hence overall average rain for the season.

Autumn climate: 1981 to 2010 average mean temperature 11 or 12°C but nearer 10°C in rural areas. Maximum temperatures average 14 to 16°C. November normally colder than October which is colder than September. Average 1981 to 2010 rain 300 to 400mm, 600 to 800mm over the moors but east of the moors and in lowland Somerset more like 200 to 300mm. September often drier than October or November.

Winter 2019  (December January February) minimal data. 

Milder than average throughout. Wetter start to winter then ending below average. Below average snowfall.

Winter Climate: 1981-2010 average temperature values for lowland areas 7°C in the West and 5°C in the East. Rainfall; Dec and Jan typically wetter than February. 1981-2010 Autumn average 300-400 mm lowlands but 200-300 mm areas to E of Dartmoor. Snow climatology less than 5 days lying snow over lowland areas 5 to 10 hills, say hills around 200 metre elevation – one in three years have no lying snow.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary can be seen at  here.

The attempt at a Regional Forecast for SW England aims to test whether such a forecast of temperature and rainfall variation from average can be made using numerical model data available on the internet. The forecast should not be used for any other purpose. A brief verification summary for the UK and Eire is routinely published at http://www.weather-info.co.uk/wxsvc/Verification.html or Click here for the Teignmouth and Dawlish summary

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

NMME information:   http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-12-00050.1

CFS2  info

GLOFAS Acknowledgement: Data were provided by the Global Flood Awareness System – GloFAS (http://www.globalfloods.eu/) of the European Commission Joint Research Centre and the European Centre for Medium-Range Weather Forecasts.
Reference: Alfieri, L., Burek, P., Dutra, E., Krzeminski, B., Muraro, D., Thielen, J., and Pappenberger, F.: GloFAS – global ensemble streamflow forecasting and flood early warning, Hydrol. Earth Syst. Sci., 17, 1161-1175, doi:10.5194/hess-17-1161-2013, 2013.

‘Copernicus Products’  as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus  http://climate.copernicus.eu

International seasonal monthly data from WMO

Stratospheric Diagnostics from Japan Met Agency and Free University Berlin

Climate data from The Met Office UK and NCEP USA

Review and Experimental Long Range Forecast for SW England. March 2019.

Published 15 March 2019.

GDPR statement: Please note that the author of this blog does not set cookies but the host “wordpress.com” sets multiple cookies which are outside of the authors control. You can view their cookie policy here. 

1. Influences.

Changes in sea temperature.

The sea temperature around the UK and across much of the North Atlantic is similar to last month being fairly close to the seasonal normal, a shade warmer/cooler in places.

The Met Office diagnostic for the tropical Atlantic (shown below) was near normal with a trend to above normal values in the majority of the ensemble solutions.

In the Pacific weak El-Nino conditions have continued, see CFS2 and  multi model ensemble forecast below.

An interesting feature is the sea temperature anomaly to the west of Panama. The cold tongue is caused by up-welling of colder salty water which is probably due to the spread west of lower salinity water by persistent easterly winds.

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) has been slightly positive (warmer wetter phase for UK) since early January and the index is likely to remain in a positive phase over the short term. Longer term there are signs of a disruption in this pattern.

For NAO background information see the Met Office NAO information.

Recent Climatology

In the SW of England, March main station SYNOP data to 0600 15th shows the average temperature anomaly to be around +1.5 C, rainfall between 100 and 110% of average with about 40% of normal sunshine hours.

Temperatures over the last six months have been near or above average with February exceptionally mild and follows on from a warmer than average summer 2018.

Rainfall was above average in SW England during November and December 2018 otherwise the nine months from June 2018 has seen normal or below normal rainfall for most parts.

The wetter period in the first half of February 2019 helped river flow recover from the lows in January but river flows were reported as slightly below average.

Full details can be found in the  February 2019 Hydrological summary PDF 

The reservoir levels in the SW of England (10th March) show 87% storage which is below the normal winter level.

The experimental product from the Global Flood Awareness System (Version 2) based on early March ECMWF seasonal forecast for April to June 2019. The system does not suggest an enhanced flood risk for UK currently and suggest lower than normal river flows are possible.

Atmosphere predictions.

A:  1: Stratosphere 

The stratospheric polar vortex re-established and became unusually strong. Much colder than normal temperatures were recorded, especially at 10 and 30hPa.  Recent forecasts (ECMWF shown below) suggest a new area of warming is likely to develop and this may well be the final warming prior to the change to a “summer” pattern. This may fit in with some forecasts of more blocking patterns and the lower than average river flow forecast shown by Glofas.

A 2: Upper Troposphere

CFSv2 200hPa monthly mean forecast height (contours) and anomaly (lower row).

Some indication of enhanced jet in April with a SSW jet possibly steering lows further N over or to N of UK on average. More generally ridged pattern for May and June but less of a signal for July and August.

B: Lower Troposphere:

Selection of Spring (April May June and some July August) solutions. Top row temperature anomaly and lower row precipitation anomaly. Above normal orange/reds below normal in blue shades.

ECMWF monthly

CFS2 E3 monthly

NMME monthly 

Selection of models UKMO, Australia, Russia, France, Canada and Germany. Left image season April to June then separate months. Top row temperature anomaly and lower row precipitation anomaly.  Russia and Australian colder and wetter most others warmer drier after a wetter start and possible end of the period April to August. Other models available at web link.

This slideshow requires JavaScript.

C: Recent results for the winter period December January February:

Temperature mostly fair indication (scale no indication poor fair good)  but signal for the milder February was confused by the colder indication due to a sudden stratospheric warming which although blocked patterns developed the flow remained mild rather than colder easterly. Rainfall good indication for December but poor overall for the season being wetter than average. Pressure was above average so at best only a partial signal. Better models seemed to be NMME and Japan.

2. Forecast. SW England.

Remainder of Spring 2019  (April May) 

Milder than average temperatures continue for both for April and May in the SW o England.

Rainfall totals normal to wetter than normal in April but trending to drier than average in May.

Spring climate: 1981-2010 average mean temperature 9 or 10°C but a few degrees cooler over the moors. Roughly Mar 7 or 8°C Apr 8 or 9°C  May 11 or 12°C. Average 1981 to 2010 rain 200 to 300mm lowest values in E Devon and over parts of Somerset.

Summer 2019  (June July August) 

Warmer than average summer although temperatures in August may be closer to normal.

Overall near or below normal rainfall seems likely but uncertain as to whether it is the number of dry days or the rain total that will be lower. Higher temperatures may lead to shorter periods of heavier rain but fewer wet days which has been a pattern in recent years.

Several models suggest a drier than average June and possibly July although some suggest August rather than July to be drier. Probably an increased risk of at least normal rainfall later in the summer. Overall monthly details is inconsistent but the idea that the start of summer could be the drier period seems well supported although this is different to February data.

Chance of reduced river flows and reservoir levels causing some concerns.

Summer climate: 1981 to 2010 average daily mean temperature 14 or 15°C in many areas to 16 or 17°C in main urban areas also locally east of the moors and more widely in Somerset. Maximum temperatures average 19 to over 21°C in similar areas. July often warmer than August. Average 1981 to 2010 rain 300mm over the moors, typically 200 to 250mm in many coastal and eastern areas. June often drier than July and July drier than August.

Autumn 2019  (September October November). 

Warmer September then milder than normal, monthly and for the season.  Could start drier in September then  be a wetter than average start to Autumn in the SW but then near or even below normal rainfall possible for for October or November.

Autumn climate: 1981 to 2010 average mean temperature 11 or 12°C but nearer 10°C in rural areas. Maximum temperatures average 14 to 16°C. November normally colder than October which is colder than September. Average 1981 to 2010 rain 300 to 400mm, 600 to 800mm over the moors but east of the moors and in lowland Somerset more like 200 to 300mm. September often drier than October or November.

Winter 2019  (December January February) minimal. 

Milder than average throughout. Wetter December then below average rainfall hence a drier than average winter. Below average snowfall.

Winter Climate: 1981-2010 average temperature values for lowland areas 7°C in the West and 5°C in the East. Rainfall; Dec and Jan typically wetter than February. 1981-2010 Autumn average 300-400 mm lowlands but 200-300 mm areas to E of Dartmoor. Snow climatology less than 5 days lying snow over lowland areas 5 to 10 hills, say hills around 200 metre elevation – one in three years have no lying snow.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary can be seen at  here.

The attempt at a Regional Forecast for SW England aims to test whether such a forecast of temperature and rainfall variation from average can be made using numerical model data available on the internet. The forecast should not be used for any other purpose. A brief verification summary for the UK and Eire is routinely published at http://www.weather-info.co.uk/wxsvc/Verification.html or Click here for the Teignmouth and Dawlish summary

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

NMME information:   http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-12-00050.1

CFS2  info

GLOFAS Acknowledgement: Data were provided by the Global Flood Awareness System – GloFAS (http://www.globalfloods.eu/) of the European Commission Joint Research Centre and the European Centre for Medium-Range Weather Forecasts.
Reference: Alfieri, L., Burek, P., Dutra, E., Krzeminski, B., Muraro, D., Thielen, J., and Pappenberger, F.: GloFAS – global ensemble streamflow forecasting and flood early warning, Hydrol. Earth Syst. Sci., 17, 1161-1175, doi:10.5194/hess-17-1161-2013, 2013.

‘Copernicus Products’  as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus  http://climate.copernicus.eu

International seasonal monthly data from WMO

Stratospheric Diagnostics from Japan Met Agency and Free University Berlin

Climate data from The Met Office UK and NCEP USA

Review and Experimental Long Range Forecast for SW England. Feb 2019.

Published 23 February 2019 slightly later than normal.

GDPR statement: Please note that the author of this blog does not set cookies but the host “wordpress.com” sets multiple cookies which are outside of the authors control. You can view their cookie policy here. 

1. Influences.

Changes in sea temperature.

The sea temperature around the UK and across much of the North Atlantic is fairly close to the seasonal normal, a shade warmer/cooler in places.

The Met Office diagnostic for the tropical Atlantic (shown below) was near normal with a trend to above normal values in the majority of the ensemble solutions.

In the Pacific weak El-Nino conditions have established, see CFS2 and  multi model ensemble forecast below.

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) has been slightly positive (warmer wetter phase for UK) since early January and the index is likely to remain in a positive phase over the short term.

For NAO background information see the Met Office NAO information.

Recent Climatology

In the SW of England February main station SYNOP data to 0600 23rd February shows the average temperature anomaly at between +1.6 and +1.9 C, rainfall at around 70% of average and about 90% of normal sunshine hours.

December 2019 was milder than average, January 2019 saw close to normal temperatures and so far February has been mild resulting in a milder the average “winter” (DJF).

 

November and December 2018 were wetter than average across the SW but October 2018 and January 2019 were drier. So far February has been slightly below normal so that winter looks like ending up slightly drier than average across the SW

Rover flows in SW England during January reflect the recent dry weather with eastern parts of the region showing lower longer term values.

Ground water levels for eastern parts of SW England remain near normal.  Full details can be found in the  January 2019 Hydrological summary PDF 

The reservoir levels in the SW of England (17th February) show 84% storage which is below the normal winter level.

The experimental product from the Global Flood Awareness System (Version 2) based on early February ECMWF seasonal forecast for March to May 2019. The system does not suggest enhanced flood risk for UK currently. To date this system has not be a useful guide.

Atmosphere predictions.

A:  1: Stratosphere 

A sudden stratospheric warming (SSW) took place during December and JMA issued a STRATALERT on the 21st of December The warming became MAJOR and continued into January. An END message was issued bu JMA on the 4th February.

It appears that as far as the UK was concerned the warming did not fully extend down trough the atmosphere or perhaps the blocking pattern and High pressure location was not conducive to a colder easterly but maintained a milder S or SW flow.

A discussion on SSW evolution by Simon Lee is of interest Full text by Simon Lee December 2018

Since the end of the warming the stratosphere has returned to nearer normal conditions with stronger zonal westerlies becoming established. GFS 10 hPa zonal wind had shown a reversal but recent forecasts show a return to westerly types. Graphic below H Attard, Albany NY

At 10hPA a strong polar vortex has established and at 50hPa the ridge/block pattern is due to collapse in favour of a zonal type. A final warming (end of winter type) is not yet indicated in the 10 day ECMWF stratospheric forecast.

CFS2 climate model 10hPa polar vortex in March becoming the summer pattern in April 2019.

A 2: Upper Troposphere

CFSv2 200hPa monthly mean forecast height (contours) and anomaly (lower row).

March April May 2019 200hPa month mean and anomaly

Some indication of enhanced jet in March to W of UK and less extent for a SSW jet in April and May possibly steering lows further N over or to N of UK on average. More generally ridged pattern for June and  August and in general above average heights throughout the forecast.

June July August 2019 200hPa month mean and anomaly

B: Lower Troposphere:

B1: Spring 2019

Selection of Spring (March April May) solutions. Top row temperature anomaly and lower row precipitation anomaly.

WMO multi model ensemble Spring 2019. (MAM and monthly anomalies) 

UKMO Spring 2019 (MAM and monthly anomalies)

NMME multi model ensemble

CFSv2 mean of 10 days output(E3 data)

ECMWF Sprin 2019 (MAM and monthly anomalies)

Common signal for SW England, above average temperatures for season and for March to be wetter and in some models also April.

B2: Summer 2019

NMME multi model ensemble JJA monthly anomalies

CFSv2 E3 mean of 10 days runs. Monthly anomalies JJA

ECMWF JJA monthly anomalies

C: Recent results for the period November December January :

Most models got December being milder. EC looked a little cool but was good with trend and got the near normal January following milder December, other models not helping with this. EC PPN not so good for November and January. CFS and NNME overly strong PPN anomalies but hinting at wetter December and less so in January which was correct. 

2. Forecast. SW England.

Spring 2019  (March April May) 

Possibly near normal temperatures in March then trending to milder than average temperatures for the season. May probably the month with the strongest signal for above normal temperature although several models suggest April could be the relatively mildest month.

A wetter than average season is likely mainly due to rainfall in the first half of the season. The middle or perhaps the end of the season may well see nearer normal rainfall but there is little agreement in month to month rainfall detail after March.

Spring climate: 1981-2010 average mean temperature 9 or 10°C but a few degrees cooler over the moors. Roughly Mar 7 or 8°C Apr 8 or 9°C  May 11 or 12°C. Average 1981 to 2010 rain 200 to 300mm lowest values in E Devon and over parts of Somerset.

Summer 2019  (June July August) 

Warmer than average summer but with temperatures in June nearer normal and August more likely to be much warmer than average.

A wetter start to summer in June but then drier than normal above normal rain although  there is some indication that June could be drier. Probably below normal rainfall for the season as a whole.

Chance of reduced river flows and reservoir levels causing some concerns.

Summer climate: 1981 to 2010 average daily mean temperature 14 or 15°C in many areas to 16 or 17°C in main urban areas also locally east of the moors and more widely in Somerset. Maximum temperatures average 19 to over 21°C in similar areas. July often warmer than August. Average 1981 to 2010 rain 300mm over the moors, typically 200 to 250mm in many coastal and eastern areas. June often drier than July and July drier than August.

Autumn 2019  (September October November) limited data. 

Milder than normal monthly and for the season.  Could be a wetter than average start to Autumn in the SW but then near or even below normal rainfall possible for for October or November.

Autumn climate: 1981 to 2010 average mean temperature 11 or 12°C but nearer 10°C in rural areas. Maximum temperatures average 14 to 16°C. November normally colder than October which is colder than September. Average 1981 to 2010 rain 300 to 400mm, 600 to 800mm over the moors but east of the moors and in lowland Somerset more like 200 to 300mm. September often drier than October or November.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary can be seen at  here.

The attempt at a Regional Forecast for SW England aims to test whether such a forecast of temperature and rainfall variation from average can be made using numerical model data available on the internet. The forecast should not be used for any other purpose. A brief verification summary for the UK and Eire is routinely published at http://www.weather-info.co.uk/wxsvc/Verification.html or Click here for the Teignmouth and Dawlish summary

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

NMME information:   http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-12-00050.1

CFS2  info

GLOFAS Acknowledgement: Data were provided by the Global Flood Awareness System – GloFAS (http://www.globalfloods.eu/) of the European Commission Joint Research Centre and the European Centre for Medium-Range Weather Forecasts.
Reference: Alfieri, L., Burek, P., Dutra, E., Krzeminski, B., Muraro, D., Thielen, J., and Pappenberger, F.: GloFAS – global ensemble streamflow forecasting and flood early warning, Hydrol. Earth Syst. Sci., 17, 1161-1175, doi:10.5194/hess-17-1161-2013, 2013.

‘Copernicus Products’  as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus  http://climate.copernicus.eu

ECMWF seasonal monthly data from weather.us

Stratospheric Diagnostics from Free University Berlin

Climate data from The Met Office UK and NCEP USA.

Review and Experimental Long Range Forecast for SW England. January 2019.

Published 18 January 2019

GDPR statement: Please note that the author of this blog does not set cookies but the host “wordpress.com” sets multiple cookies which are outside of the authors control. You can view their cookie policy here. 

1. Influences.

Changes in sea temperature.

The sea temperature around the UK and across much of the North Atlantic has seen a change to above normal values, although the Met Office diagnostic for the tropical Atlantic (shown below) was slightly below normal at the start of January. This follows a mild start to January for the UK and much of the North and West of Europe (but not the South and East).

Met Office Tropical North Atlantic analysis and forecast

 

The fairly modest El Nino in the Pacific is now forecast to be slightly less strong than previous forecasts and may not impact on the UK weather for the remainder of Winter and into Spring.

ENSO Nino 3.4 area forecast CFS2 and NMME

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) has been slightly positive (warmer wetter phase for UK) since early January and there is only a weak signal for a negative phase in the NOAA CPC forecast for two weeks from 17th Jan.

For NAO background information see the Met Office NAO information.

Recent Climatology

In the SW of England January data to the 18th shows temperatures above average 0.5C in the east to over 1C in the west. Rainfall and sunshine have been very low. Anomalies for Europe in week 2 are shown below.

Over the last six months or so temperatures have been above the long term average

 

and rainfall near or mostly only a little below average thanks to a wet December in the south.

Rover flows and ground water levels in SW England during December reflect the reflect the wetter November and December but some northern and eastern parts of the UK continue to have reduced river and ground water levels..

Full details can be found in the  December 2018 Hydrological summary PDF 

The reservoir levels in the SW of England (13th January) show 78% storage which is below the normal winter level.

The experimental product from the Global Flood Awareness System (Version 2) based on early January ECMWF seasonal forecast for February to April 2019. To date this system has not be a useful guide. The current EC seasonal forecast does suggest well above average rain in the southern half of UK for Feb and March but not April. Only a minority of the flood solutions suggest above normal river flow for London, slightly higher numbers for the western end of the Thames hence river flows in some SW parts may not be correct.

Atmosphere predictions.

A:  1: Stratosphere 

A sudden stratospheric warming (SSW) took place during December and JMA issued a STRATALERT on the 21st of December, the warming became MAJOR and has continued.

Note not all seasonal models cover events in the stratosphere but UKMO CFS2 and ECMWF certainly have layers into the stratosphere. A sudden stratospheric warming is more often than not (but not always) followed by a change of type for the UK weather to a more blocked pattern with possibly colder easterly types.

A recent study by Karphechko et al. (2017) suggests that around 43% of SSW do not propagate downward to influence the troposphere. Simon Lee (PhD student studying the stratosphere and S2S forecasting, University of Reading) wrote on 27th Dec 2018:

“Major stratospheric sudden warming events (SSWs) attract widespread attention because they are now known to have significant impacts on the tropospheric circulation (e.g. Baldwin and Dunkerton 2001, hereafter BD01). Anomalies in the stratospheric circulation (often expressed as the Northern Annual Mode (NAM) index, or polar cap geopotential height anomalies) propagate downwards through the stratosphere into the troposphere, rather like “dripping paint” (such as BD01 Fig. 2). A major SSW is associated with the development of a negative NAM in the stratosphere; the “typical” response is the development of a negative NAM (or the associated NAO/AO) in the troposphere ~10-14 days after the central date of the SSW (when the 10 hPa 60N zonal-mean zonal wind becomes easterly) which can persist for several months.

However, not all SSWs were created equal – and some SSWs do not strongly couple to the tropospheric circulation. A recent study by Karphechko et al. (2017) classified major SSWs as “downward propagating” (dSSW) or otherwise (nSSW) based on the 1000 hPa NAM index following the event, and found 43% were nSSW – i.e., not followed by a strong and persistently negative surface NAM. This is not a small fraction of SSWs, and the atmospheric evolution following the two types was found to be significantly different.

Our perception of SSWs in recent years has been highly influenced by a relatively unusual clustering of vortex-split, downward-propagating events (Jan 2009, Feb 2010, Jan 2013 and Feb 2018) which all had similar tropospheric impacts (all 4 of those events were followed by an outbreak of snow/cold in the UK, for example). The most recent nSSW occurred in Feb 2008. Thus, the announcement of a major SSW – particularly on social media – has become synonymous with a specific weather pattern.” 

Full text by Simon Lee December 2018

ECMWF data for 10 hPa and 150hPa suggest that full coupling has not yet happened. The latest forecast at 10 hPa shows the polar stratospheric vortex forming again,

GFS 10 hPa zonal wind had shown a reversal but recent forecast suggest a return to climatology. Graphic below H Attard, Albany NY

CFS2 climate model has been forecasting a return of the 10 hPa polar vortex in February for some time. A recent 10hPa forecast for Feb Mar and Apr is show below.

A 2: Upper Troposphere

CFS2 200hPa 8th January 2019 data for the Feb to May 2019. The below normal heights in February might imply a more cyclonic even easterly pattern for a time. But the above normal heights suggest less unsettled types for the S of the UK after February but with the chance of stronger than normal Atlantic jet flow suggesting disturbed weather especially in the North of UK.

B: Lower Troposphere:

B1: February to March seasonal graphic  –  temperature anomaly. Top row Met Office, lower row multi model ensemble (not ECMWF). Run from 1st of January.

February to March seasonal graphic  –  precipitation anomaly. Top row Met Office, lower row multi model ensemble (not ECMWF)

Combined temperature and precipitation anomaly forecasts Feb to May seasonal forecast graphics: Red above and below below normal.

B2: NMME data 8th Jan 2019

B3: ECMWF 14th January 

B4: GFS2 E3 version mean of 10 days output (00 06 12 and 18UTC) each with 4 runs of the model.

First version on the 6th of Jan

Second version on the 12th of Jan

We can perhaps get an idea that seasonal models run later in January have picked up a change to colder types, eg: the later version of the GFS and to some extent the Met Office output.

Another feature in CFS and UKMO is for the south the be see above normal precipitation as well as being colder, leading to an increased snow risk for southern half of UK. Below is CFS2 for February with data up to 16th of January.

The main problem seems to be after a colder start to February how long into the month is this likely to last, 2 or perhaps 3 weeks. Data up to 18th suggests slightly less cold in week 2 and more widely in the week from the 15th February.

B5: For the summer models agree on normal or above normal temperatures but less clear on rainfall. The NMME graphic below shows July wetter in the South but little agreement in this detail.

C: Recent results:

A few models did quite well with the October to December period but typically models over forecast the temperature positive anomaly and have poor matches to rainfall distribution over the UK. A look at how “good” seasonal forecasts have been can be seen at the review page.

2. Forecast. SW England.

Remainder of Winter (February 2019).

A cold start to February is likely but probably returning to near normal by around mid month. Rainfall is likely to be above average across SW England and there is an increased risk of snow especially over the hills/moor but some snow cannot be ruled out elsewhere especially at the start of the month.

February Climate: 1981-2010 Temperature; average temperature values for lowland areas 5 or 6°C but over 6°C in West Cornwall. Rainfall;  February. 1981-2010 average 80-100mm mm lowlands but 60-80mm in areas to E of Dartmoor and 40-80mm East of Exmoor. Over the Moors 100-250mm. .

Spring 2019  (March April May) 

Possibly near normal temperatures in March then trending to milder than average temperatures for the season. May probably the month with the strongest signal for above normal temperature.

A wetter than average season is likely mainly due to rainfall in the first half of the season. The end of the season may well see nearer normal rainfall but there is little agreement in month to month rainfall detail with some models showing May wetter.

Spring climate: 1981-2010 average mean temperature 9 or 10°C but a few degrees cooler over the moors. Roughly Mar 7 or 8°C Apr 8 or 9°C  May 11 or 12°C. Average 1981 to 2010 rain 200 to 300mm lowest values in E Devon and over parts of Somerset.

Summer 2019  (June July August) based on limited data.

Slightly warmer than average summer with near or slightly above normal rain although  there is some indication that June could be drier.

Summer climate: 1981 to 2010 average daily mean temperature 14 or 15°C in many areas to 16 or 17°C in main urban areas also locally east of the moors and more widely in Somerset. Maximum temperatures average 19 to over 21°C in similar areas. July often warmer than August. Average 1981 to 2010 rain 300mm over the moors, typically 200 to 250mm in many coastal and eastern areas. June often drier than July and July drier than August.

Autumn 2019  (September October November) early indications only. 

Milder than normal. Possibly starting warmer in September and then trending near normal later in the season. Wetter than average season but monthly data trending nearer normal later.

Autumn climate: 1981 to 2010 average mean temperature 11 or 12°C but nearer 10°C in rural areas. Maximum temperatures average 14 to 16°C. November normally colder than October which is colder than September. Average 1981 to 2010 rain 300 to 400mm, 600 to 800mm over the moors but east of the moors and in lowland Somerset more like 200 to 300mm. September often drier than October or November.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary can be seen at  here.

The attempt at a Regional Forecast for SW England aims to test whether such a forecast of temperature and rainfall variation from average can be made using numerical model data available on the internet. The forecast should not be used for any other purpose. A brief verification summary for the UK and Eire is routinely published at http://www.weather-info.co.uk/wxsvc/Verification.html or Click here for the Teignmouth and Dawlish summary

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

NMME information:   http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-12-00050.1

CFS2  info

GLOFAS Acknowledgement: Data were provided by the Global Flood Awareness System – GloFAS (http://www.globalfloods.eu/) of the European Commission Joint Research Centre and the European Centre for Medium-Range Weather Forecasts.
Reference: Alfieri, L., Burek, P., Dutra, E., Krzeminski, B., Muraro, D., Thielen, J., and Pappenberger, F.: GloFAS – global ensemble streamflow forecasting and flood early warning, Hydrol. Earth Syst. Sci., 17, 1161-1175, doi:10.5194/hess-17-1161-2013, 2013.

‘Copernicus Products’  as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus  http://climate.copernicus.eu

ECMWF seasonal monthly data from weather.us

Stratospheric Diagnostics from Free University Berlin

Climate data from The Met Office UK and NCEP USA.