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.

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Review and Experimental Long Range Forecast for SW England. December 2018.

Published 17 December 2018

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 in the North Sea remains above normal and temperatures in the N and E Atlantic (west of the UK) slow slightly less of a cool anomaly compared to last month. The sea temperature remains above normal south of 50 deg north and west of 20 deg West across to Florida but is cooler near the equator.

UKMO December 2018 Tropical North Atlantic SST forecast

The tropical North Atlantic SST has been below the forecast value from last month but is forecast to return to near average. In the Pacific the El Nino is well established (see graphic below) and is forecast to remain through to Autumn 2019.

The dominant IRI statistical predictor for UK rainfall based on the Pacific sea temperature anomalies for the winter season is shown below. Probabilities shown are for “near normal” precipitation, which is the category which has higher probs than either below or above normal.

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) has been swapping between a positive and negative and is forecast to continue to oscillate over the next month but with no strong signal for a negative phase. See below.

For NAO background information see the Met Office NAO information.

Recent Climatology

In the SW of England data to December 16th shows temperatures above average by over two degrees, above normal rain and well below average sunshine. November also saw well above average temperatures although earlier months were nearer average. Rainfall in November was above average but the longer term rain total remains lower than normal (see below).

Recent rainfall has boosted soil moisture and the forecast (GFS) is for more rain to come in December hence increases in soil moisture.

Rover flows in November reflect the reflect the wetter November and December although rivers in the east of SW England were still lower reflecting the longer term rainfall deficit.

Ground water has improved to near normal see details in the November Hydrological Summary which can be viewed here – November 2018 summary PDF 

The reservoir levels in the SW of England (9th December) show 69% storage which is a big increase since last month due to the wetter November and first half of December.

The experimental product from the Global Flood Awareness System (Version 2) based on early December ECMWF seasonal forecast for December to  March. To date this system has not be a useful guide. The current EC seasonal forecast does not suggest well above average rain hence no or very low flood signal.

Atmosphere predictions.

A:  Stratosphere and Upper Troposphere

The stratospheric polar vortex was well establish with temperatures in line with the normal variations but in the last week or so marked warming has begun leading to a forecast re-positioning of the polar vortex and a forecast stratospheric wind reversal over the USA an d Pacific. It is not yet clear if this reversal/weakening of the stratospheric wind flow will extend to the UK area but it at least seems probable. THIS MAY HAVE STRONG IMPACT on the forecast for the remainder of the winter but as yet models only suggest N America surface temperature cools markedly in January compared to earlier forecasts (to well below normal) and that N/NE Europe and Russia becomes colder than normal in February.

ECMWF 50hPa forecast data 15th December 1200UTC

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.

CFS2 200hPa 8th December 2018 data for the January to March 2019 period continues to suggest above normal heights across the S of the UK and  imply enhanced Atlantic jet flow in January suggesting disturbed weather.

CFS2 Jan to March 2019 mean 200hPa height and anomaly forecast.

CFS2 March to May 2019 mean 200hPa height and anomaly forecast.

For the Spring period there is a hint of below normal 200hPa heights in March over NE Uk may imply more cyclonic N or NW flows then above normal heights return.

B: Lower Troposphere:

Graphics for January to March 2010 –  comparison of ECMWF NMME and CFS2(E3 version). Top row are temperature anomaly and lower row rain rate anomaly. Red/oranges are above “model hindcast” normal and blue below.

ECMWF December data monthly forecast temp and rain anomaly JFM 2019

 

CFS2 December data monthly forecast temp and rain anomaly JFM 2019 

CFS2 December data monthly forecast temp and rain anomaly JFM 2019 

In most of the output there are indications for above normal temperature and rain in the SW of UK for the three month period though with differing ideas of which month could be drier.

For the March to May period comparison graphics are shown below:

ECMWF December 2018 data for March to May 2019

CFS2 (E3) December 2018 data for March to May 2019

NMME December 2018 data for March to May 2019

Near or slightly above normal temperatures are indicated and some agreement that April could be drier than normal.

C: Recent results:

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.

Remainder of Winter (January and February 2019).

161218 – Caution marked stratospheric warning occurring/forecast to occur next two weeks which might impact the remainder of winter forecast and change to colder easterly types.

Main consensus is for near or above average temperatures for January but nearer normal in February and perhaps even slightly colder than average.

January is likely to be wetter than average with average snow risk. February probably nearer normal rainfall but with an increased snow risk especially for the moors.

Winter Climate: 1981-2010 average temperature values for lowland areas 7°C in the West and 5°C in the East. Rainfall;  January 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.

Spring 2019  (March April May) based on less data.

Possibly near normal or a colder than average March then recovering to milder than average temperatures for the season, with May probably the month with the strongest signal for above normal temperature.

A wetter than average season is likely with increased snow risk for March, mainly over the hills. April could be the drier of the months with May wetter than average.

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 very limted data.

Another warmer than average summer with slightly above normal rain although the number of wet days may be below average and 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.

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. November 2018.

Published 17 November 2018

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 near and to the East of the UK remains above normal but is likely to cool as strong easterlies develop over the next few days. The northern North and Northeast Atlantic is below normal as are the Great Lakes given how warm it was in this area at the end of October.

The tropical Atlantic is trending to near normal and in the Pacific the El Nino is established as can be seen in the above plots.

The dominant IRI statistical predictor for UK rainfall based on the Pacific sea temperature anomalies for the winter season is shown below. Probabilities shown are for “near normal” precipitation, which is the highest category.

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) had been mostly in a positive phase as forecast turned sharply negative near the end of October and after a recover is forecast to again turn sharply negative: see below.

Conditions applicable to a persistent negative NAO are shown by the Met Office graphic below:

However the persistence of a negative NAO is not yet certain. For NAO background information see the Met Office NAO information.

Recent Climatology

Temperatures during September and October in SW England were near average following an unusually warm summer and so far November has been well above average but due to the cold spell about to start may well end up near average. Rainfall in September and October was mostly a little below average and followed a drier than average summer. November is currently near or a little above average rainfall so may well end up slightly above average.

Despite recent rainfall soil moisture remains below normal across SW England.

Rover flows in October reflect the longer term drier period.

Groundwater levels in Eastern parts of SW England are near normal and the November outlook (below right) suggest the main problem areas are further east.

The October Hydrological Summary can be viewed here – October 2018 summary PDF 

The reservoir levels in the SW of England (11th November) show 55% storage which is a slight increase since last month due to the wetter start to November.

The experimental product from the Global Flood Awareness System (Version 2) based on early November ECMWF seasonal forecast for November to February.

Atmosphere predictions.

A:  Stratosphere and Upper Troposphere

The N Pole stratosphere is cooling in line with normal variations.

The polar vortex formed in October and has migrated SW of the pole. Forecasts show a splitting of the vortex and reduced stratospheric flow over Europe for a time before reforming again after about a week. This is illustrated in the 50hPa forecast sequence shown below.

FS2 200hPa data (as supplied to NNME data set October 2018) for the December to February 2019 period continues to suggest above normal heights across the UK. for both December and January there are signs of enhanced jets suggesting stormy spells at least for the north of the UK.

CFS2 200hPa 7th Nov 2018 data (missing from NNME data set) for the December 2018 to February 2019 period continues to suggest above normal heights across the UK during the winter period. Anomalies imply enhanced Atlantic jet flow suggesting disturbed weather for northern UK in particular during December and the far north in February.

CFS2 mean 200hPa contour and anomaly forecast Dec Jan Feb.

B: Lower Troposphere:

The Copernicus multi model ensemble has been upgraded with the addition of models from Italy and Germany adding to ECMWF, UKMO and MeteoFr. The winter forecast is shown below.

Copernicus Temperature mean anomaly forecast 

Copernicus Rainfall mean anomaly 

CFS2 (E3) 10 day mean of model output for the winter months (December January and February). Oranges/red are above “model normal” blues are below.

NMME mean of model output for the winter months (December January and February). Oranges/red are above “model normal” blues are below.

ECMWF mean of model output for the winter months (December January and February). Oranges/Purple are above “model normal” blues are below.

There is good agreement for above normal temperatures in December and an indication than anomalies could be lower or negative in February. Rainfall is much more variable but a signal for wetter December may offset less wet month to follow.

For Spring graphics see seasonal latest.

C: Recent results:

A review of how useful forecast have been can be seen at the review page.

For the period August to October using July 2018 data the following marking was given (good/fair/poor/no signal) for the UK.

Original text Summary – Good – Slightly optimistic temperature but idea of the west trending to normal was good as was the idea of higher than average pressure. Rainfall trend towards normal was fair and the idea of the of the north becoming above normal was good. 
1. Russia: Temp fair . PPN poor .
2. USA – CFS2 : Temp good . PPN fair .
3. UKMO Contingency: Temp fair . PPN good .
4. UKMO : Temp poor . PPN poor . PMSL poor .
5. USA – IRI : Temp no signal . PPN good .
6. KMA APCC : Temp fair . PPN fair .
7. JMA : Temp fair . PPN good . PMSL fair
8. NMME : Temp fair . PPN good .
9. IMME – Temp fair . PPN fair .
10. BCC – Temp fair . PPN fair .
11. NASA – Temp poor . PPN fair .
12. Brazil: Temp fair . PPN good PMSL fair .
13. CanSips : Temp fair . PPN poor .
14. SAWS: not available
15. Copernicus Temp good . PPN no signal . PMSL good
16. EC Temp good Temp fair . PPN no signal . PMSL poor
17. MF Temp fair. PPN fair . PMSL fair
18. JAMSTEC:
19: KMA: Temp fair . PPN fair. PMSL poor
20: ECMWF (monthly) Temp: fair PPN: fair

Last winter most seasonal forecast output based on November data, was poor.

2. Forecast.

Winter 2018/9  (December January and February).

Main consensus is for near or above average temperatures for the season but starting off milder than average and ending less mild and perhaps even slightly below normal.

Rainfall likely to be near or above normal for the season with the wetter month compared to average being December.

Below average snowfall is likely with the highest risk of snow possibly late in the winter and chiefly over the moors.

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.

Spring 2019  (March April May) based on less data.

Possibly near normal or a colder than average March then recovering to milder than average temperatures for the season.

March may be wetter than average with increased snow risk. April and May probably near normal or a little wetter than average.

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 very limted data.

Another warmer than average summer with above normal rain although the number of wet days may be below average.

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.

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. October 2018.

Published 20 October 2018

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 remains well above normal in the south but has shown some cooling in the north. The northern North Atlantic remains below normal as is the Great Lakes area which is a little surprising given the milder than average temperatures in the area over the later month or so. Recent tropical storms do not seem to have material depressed sea temperatures to the S and E of the USA and transition towards El Nino can be seen in the Pacific.

Met Office plot of tropical North Atlantic sea temperature (above right) seems to have picked out a colder area but in the Pacific there is broad inter-model agreement for an El Nino (Enso 3.4 area) and possibly a longer lasting event than previously forecast.

The dominant IRI statistical predictor for UK rainfall based on the Pacific sea temperature anomalies for the winter season is shown below. Probabilities are for “near normal” precipitation,

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) had been mostly in a positive phase but is forecast to turn sharply negative in a week or so reflecting the cold northerly plunge into UK/Central Europe after the 26th of October rather than increased Atlantic mobility although this may occur in the far North of the Atlantic.

For background information see the Met Office NAO information.

Recent Climatology

Temperatures during September in SW England were near average following an unusually warm summer. Rainfall in September was near or a little below average and followed a drier than average summer.

Although there has been some significant rainfall recently, after the preceding drier months soil moisture content remains below normal in the south of UK. The present dry spell looks like reducing the water content further; as shown by the GFS analysis and forecast below.

Rover flows in September reflect the longer term drier period being near or below normal for September and more especially the June to September period. Ground water in the east of the region is was near normal. The full Hydrological Summary for September can be viewed here – September 2018 summary PDF 

The reservoir levels in the SW of England (14th October) show 51% storage which is a further decrease since last month although recent heavier rain has caused a slight uptick in levels.

The experimental product from the Global Flood Awareness System based on early October ECMWF seasonal forecast for October to January. It should be noted that severe flooding due to tropical storms has not been captured this year and it is likely that the system is better suited to persistent broad scale rain types. This month the output does not indicate a preference for below or above normal area rainfall but has local river flow shown as above (blue) or below (orange) normal.

Atmosphere predictions.

A:  Stratosphere and Upper Troposphere

The N Pole stratosphere is cooling in line with normal variations and the polar vortex has formed as shown by the 30hPa analysis on the 19th October 2018.

CFS2 200hPa data (as supplied to NNME data set October 2018) for the December to February 2019 period continues to suggest above normal heights across the UK. for both December and January there are signs of enhanced jets suggesting stormy spells at least for the north of the UK.

Winter monthly mean 200hPa height forecast and anomaly

For Spring above normal heights predominate but with a rather more cyclonic pattern for parts of April hinted at in the anomalies.

Spring monthly mean 200hPa height forecast and anomaly

B: Lower Troposphere:

Graphics for November available via web link seasonal latest.

Comparing CFS2 NMME and ECMWF model output for the winter months (December January and February). Oranges/red are above “model normal” blues are below.

CFS2 E3 10 day mean of output. Top temp anomaly Lower precipitation rate anomaly.

NMME.  Top temperature anomaly Lower precipitation rate indication.

There is some agreement for temperature anomalies to become more positive during the winter season but rain rate anomalies are unclear and by February EC has the opposite signal to that of  NMME.

NMME data for Spring (March to May 2019) perhaps indicate a colder start to spring in the SW and a milder end with increased precipitation in April compared to average. There is perhaps an increase snow risk in the southwest in March than average following a decrease in snow in Winter.

Full size graphics and a text review of other seasonal models can be viewed at www.weather-info.co.uk/wxsvc/seaslatest.html

2. Forecast.

November 2018

Probably milder and wetter than average. See month ahead forecast  here

Winter 2018/9  (December January and February).

Main consensus is for above average temperatures for the season but perhaps starting off with near normal values in December then trending milder than average later in the winter.

Rainfall likely to be above normal for the season especially in the west with some parts of the east of SW England having near normal precipitation.

Below average snowfall is likely with the highest risk of snow possibly late in the winter and chiefly over the moors.

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.

Spring 2019  (March April May) based on less data.

Possibly a colder than average March then recovering to milder than average temperatures for the season.

March may be drier than average but with increased snow risk. April and May probably wetter than average especially April.

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 very limted data.

Another warmer than average summer according to 2 out of 3 available models with above normal rain although early summer may be drier than average.

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.

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. Sept 2018.

Published 17 September 2018

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 remains well above normal. The colder area in the northern North Atlantic has reduced in extent slightly but recent tropical storms probably resulted in the cooler than normal SST extending from off the coast of Africa towards the USA. Despite this recent cooling the forecast, shown below, remains for a slightly warmer than normal tropical Atlantic but any future storms may need to track a little further south than Florence to benefit from warmer than normal sea temperatures.

Cooling can also be seen in the Pacific following recent storms affecting Japan and the Philippines. Progress towards an El Nino state in the Pacific seems to have stalled a little, much like last months ECMWF plume suggested. For the ENSO area 3.4 the ECMWF and UKMO forecast (shown below) is just a little cooler than the CFS2 forecast (above).

The IRI statistical predictor for UK rainfall based on the Pacific sea temperature anomalies is unlikely to be of use until the El Nino has established for the winter. The graphic below shows the probs for normal precipitation this winter during an El Nino.

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) had been mostly in a positive phase but is forecast to turn neutral or negative in the next few weeks suggesting some increased in Atlantic mobility.

For background information see the Met Office NAO information.

Recent Climatology

Temperatures during August in SW England were near or above average with the summer generally above normal making 2018 one of the warmest summers on record. Rainfall in August was more variable and closer to average but for the summer as a whole it was much drier than average as can be seen in the graphics below.

Following the dry weather water content in the top of the soil remains low is likely to further reduce in most areas. See GFS analysis and forecast below.

Rover flows in August reflect the longer term drier period. Ground water in the east of the region is near normal, see the full Hydrological Summary for  August for the full details – August 2018 summary PDF 

The reservoir levels in the SW of England (9th Septemer) show 55% storage which is a further decrease since last month.

The experimental product from the Global Flood Awareness System based on ECMWF seasonal forecast for September and August data is shown below. It should be noted that recent severe flooding in North Carolina and also in China due to tropical storms was not captured by this system. It is likely that the system is better suited to persistent broad scale rain types rather than one off events as the data is typically means over a period.

Atmosphere predictions.

A:  Stratosphere and Upper Troposphere

The N Pole stratosphere is cooling more or less along the mean although there have been some colder than normal occasions and the polar vortex is forming as shown by the 30hPa analysis on the 16th.

CFS2 200hPa data (as supplied to NNME data set September 2018) for the December to February 2019 period continues to suggest above normal heights across the UK. By January enhanced jet strength across the Atlantic is indicated suggesting greater storminess for the UK. By February this is perhaps confined to the far NW.

CFS2 monthly mean 200hPa contour height (upper row) and anomaly (lower row) 

B: Lower Troposphere:

Graphics for October and November available via web link seasonal latest.

Comparing CFS2 NMME and ECMWF model output for the winter months (December January and February).

CFS2 E3 10 day mean of models. Top row temperature anomaly, lower row rain rate anomaly.

NMME data. Top row temperature anomaly, lower row rain rate indication.

ECMWF Top row temperature anomaly. Lower row rain anomaly (blue is below normal)

 

Most models forecast above normal temperatures for the remainder of Autumn and also for winter. ECMWF, however,  suggests below normal temperatures in January 2019 supported only by JAMSTEC although a few also have near normal values rather than milder temperatures.

Rainfall is a more varied picture in the models but some agreement that parts of the UK, probably the south may have above normal rain at least for December and January.

Full size graphics and a text review of other seasonal models can be viewed at www.weather-info.co.uk/wxsvc/seaslatest.html

2. Forecast.

Remainder of Autumn 2018  (October November). 

Milder than average but perhaps for November much milder than normal.

Rainfall starting below normal in October but trending wetter than average for November but uncertainty as to when the change to wetter types will start.

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 2018/9  (December January and February).

Almost no indication for a colder than normal winter. Main theme is above or well above average temperatures, with just a hint of the temperature only slightly milder than average in wither January or February, the latter being the most likely month.

Rainfall likely to be above normal for the season. There are some indications for drier periods but not much agreement between models in location or timing. May lead to some eastern parts being near average rainfall rather than above and February may be drier than average.

Below average snowfall with the highest risk of snow possibly in January and chiefly over the moors.

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.

Spring 2019  (March April May) based on limited data.

Continuing with milder than average temperatures though some months may be near average. Rainfall below normal at least for one month and probably near or below normal for the season.

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.

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. August 2018.

Published 15 August 2018

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 remains well above normal. The colder area in the northern North Atlantic shows signs of becoming relatively warmer around the Newfoundland area with the main colder than average area having transferred East and South.

The tropical Atlantic is continuing to become a little warmer than average and it perhaps interesting that the two recent tropical storms Debby and Ernesto have formed near 35 to 45 degrees North where there is a strong positive anomaly.

Left: Tropical North Atlantic UKMO. Right: CFS2 Pacific nino 3.4 area

Left: ECMWF nino 3.4 area forecast Right: UKMO nino3.4 area forecast 

In the East Pacific temperatures continue to move towards El Nino conditions, from the current neutral state.

The IRI statistical predictor for UK rainfall based on the Pacific sea temperature anomalies is unlikely to be of use until the El Nino has established. The graphic below shows the probs for normal precipitation this winter during an El Nino.

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) remains mostly in a positive phase and is forecast to remain so in the next few weeks suggesting only weak Atlantic mobility.

For background information see the Met Office NAO information.

Recent Climatology

Temperatures during August (to the 15th) in SW England have been above normal by a degree or so. Rainfall has been more variable with heavy rain on just a few days bringing totals near to the average (but in parts of Cornwall possibly a bit above normal) for half way through the month.

The image below shows the rainfall and temperature anomalies for June and July.

Following the dry weather water content in the top of the soil remains low is likely to further reduce in most areas. See GFS analysis and forecast below.

Rover flows in July mostly reflect the drier period. Ground water in the east of the region is near normal. The full Hydrological Summary for  June is available from this link  – July 2018 summary PDF 

The reservoir levels in the SW of England (12th August) show 65% storage with a slight uptick in storage following recent rainfall.

The experimental product from the Global Flood Awareness System based on ECMWF seasonal forecast was not available at the time of writing.

Atmosphere predictions.

A: Upper Troposphere

CFS2 data (as supplied to NNME data set August 2018) for September to November at 200hPa continues to suggest above normal heights across the UK and possibly reduced jet strength but with a hint of stronger jet flow in November.

CFS2 200hPa month mean and anomaly September to November 2018

CFS2 200hPa month mean and anomaly December 2018 to February 2019

B: Lower Troposphere:

September to November temperature anomaly and precipitation indication for below/above model normal. Caution ECMWF uses opposite colour scheme for above normal rain.

NMME Sept to Nov TOP: temperature anomaly LOWER: rain rate indication (blue is below normal)

CFS2 E 3 data 13th August. Sept to Nov TOP: temperature anomaly LOWER: rain rate indication (blue is below normal) 

ECMWF Sept to November Sept to Nov TOP: temperature anomaly LOWER: rain rate indication (rain rate ORANGE is below normal)

December 2018 to February 2019 temperature anomaly and precipitation indication for below/above model normal. Caution ECMWF uses opposite colour scheme for above normal rain.

NMME Dec to Feb (data 8th August 2018) (Rain rate ORANGE is above normal)

CFS2 E3 10 day mean data 13th August 2018 (Rain rate ORANGE is above normal)

ECMWF Dec to Feb (Rain rate BLUE is above normal)

Full size graphics and a text review of other seasonal models can be viewed at www.weather-info.co.uk/wxsvc/seaslatest.html

C: Recent results/comments:

UK Summary 17 April 2018 for May June July

Temperature:The main indication is for near normal temperature, perhaps starting below normal especially across the S/SW of Eire and SW of UK due to cooler than normal sea temperatures. Some models also indicate parts of NE England/SE Scotland at risk from colder that normal May due to colder N Sea temperatures. Hints at June being above normal. Strongest signal for above normal is in NW Scotland and Midlands England. Rainfall: A mixed signal. Mainly a signal for near normal rainfall for the season but also for the NW to be above normal. For models that provided monthly output the South is perhaps more likely to be drier in June than in July but it is not clear cut. Several models suggest the N and perhaps the far S could see a wetter period especially in May and July.

Result: some idea that temperature would rise from April anomalies but not generally very good. Rainfall some idea of drier June but not for the overall drier than normal period although indications that the N/NW could be wetter were OK. Score temperature poor rain fair.

Overall there was a poor indication of the very dry and very warm weather to come. More details see Verification link

2. Forecast.

Autumn 2018  (September October November) early indications. 

Milder or much milder than normal for the season as a whole and probably each month individually.

Rainfall starting below normal in September but trending wetter than average with the season probably wetter than average especially in western parts of the region. Less clear cut in the east where near normal rainfall 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 2018/9  (December January and February) limited data from 4 models. 

No indication for a colder than normal winter. Main theme is above or well above average temperatures, with just a hint of less mild in February.

Rainfall likely to be above normal for the season. There are some indications for drier periods but not much agreement between models in location or timing. May lead to some eastern parts being near average rainfall rather than above.

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  www.weatherservice.co.uk

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. July 2018 issue.

Published 18 July 2018

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.

Sea temperature around the UK remains well above  normal. In contrast a large area in the northern North Atlantic remains well below normal and according to the Met Office June issue contingency forecast: “this pattern moderately increases the probability of high pressure over Northern Europe. In summer, high pressure is associated with above-average temperatures”.

The tropical Atlantic is showing signs of becoming warmer than average and the East Pacific is trending towards El Nino conditions, from the current neutral state.

Left: UKMO Tropical North Atlantic forecast. Right CFS2 ENSO 3.4 forecast.

ECMWF ENSO 3.4  SST forecast

GFS and ECMWF more or less in line suggesting the max anomaly is likely to be in November/December 2018 followed by some cooling (relative to average).

The IRI statistical predictor for UK rainfall based on the Pacific Sea Temperature anomalies is unlikely to be of use until the Autumn when there is a forecast EL Nino state. The graphic below shows the probs for normal precipitation during an El Nino this winter.

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) has been mostly positive for some time. The move to a negative state was shorted lived and the latest forecast suggests another short dip before returning to a positive suggesting weak or no Atlantic mobility in the next few weeks.

For background information see the Met Office NAO information.

Recent Climatology

July so far in SW England has seen under half the 1981-2010 average rainfall, more sunshine than normal and much higher temperatures. Temperature anomalies running at over 3 deg C above the long term average.

For England and Wales an interesting scatter plot for JUNE 2018 was produced in the Hydrological Summary showing 1976 was warmer and 1921 and 1925 was drier.

Anomalies for the UK as a whole, temperature shown are Spring and June with rainfall June and April to June 2018:

Following the dry weather water content in the top of the soil has reduced and is likely to further reduce in most areas. See GFS analysis and forecast below.

Rover flows in June reflect the recent drier period. The full Hydrological Summary for  June is available from this link  – June2018 summary PDF 

Interestingly ground water levels for eastern parts of SW England were average or above average during June – see the full report for details.

The reservoir levels in the SW of England (15th July) show 75% storage but are following a path typical of a dry year and reducing sharply.

The experimental product from the Global Flood Awareness System suggests no enhanced flood risk, compared to the average risk, for the SW of England for the four months starting 1st July 2018 and based on ECMWF seasonal forecast.

Atmosphere predictions.

A: Upper Troposphere

CFS2 data (as supplied to NNME data set July 2018) for September to November at 200hPa continues to suggest above normal heights across the UK and possibly reduced jet strength until November.

200hpa mean height and anomaly Sep to Nov 2018

200hPa mean height and anomaly December 2018 to February 2019

Enhanced jet possible in December but much less likely in February.

B: Lower Troposphere:

August to November temperature anomaly and precipitation indication for below/above model normal. Caution ECMWF uses opposite colour scheme for above normal rain.

NMME top temperature bottom precipitation (orange above normal)

CFS2 (E3 version 10 day average) Top temperature anomaly bottom precipitation anomaly (orange above normal)

ECMWF top temperature anomaly bottom precipitation anomaly (BLUE ABOVE normal)

Above normal temperatures suggested. Hints at a risk of increased rain in August but more especially in November.

December 2018 to February 2019.

 

NMME DEC 2018 to FEB 2019 top temperature anomaly bottom above/below normal precipitation (blue below normal)

Full size graphics and a text review of other seasonal models can be viewed at www.weather-info.co.uk/wxsvc/seaslatest.html

C: Recent results/comments:

UK Summary issued March for April May June – “Summary – 170318 – Temperature for the season starting normal or below normal ending above normal hence overall could be close to normal for the season. Sea temperature near N Sea may stay below normal helping hold back temperatures for parts of NE or E of England. Rainfall likely to be below average in the S and SW of UK and Eire but above in the north. Some indication that May could be the wetter month for the south and April the drier month for some western areas but in generally not much agreement between models for month to month detail.” 
Verdict on summary: Temperature Fair did get warmer. Rainfall below average signal for S good but below average was more widespread. April detail not good though some hints at locally wetter in S England in May.

Poor indication for the very dry June or the record warmth. One of the problem with ensemble means?

Full size graphics and a text review of other seasonal models can be viewed at www.weather-info.co.uk/wxsvc/seaslatest.html

2. Forecast.

Remainder of Summer 2018  (August). 

Above normal temperatures are likely to continue through August but perhaps not with such a large anomaly as July.

August rainfall is not clear cut with mixed indications. Probably much nearer normal than of late and possibly wetter than average, perhaps due to thunder showers. It is uncertain whether wetter could be due to a greater number of “wet” days or higher rainfall rates typical of a thundery type. The latter has been a feature recent rainfall patterns and can occur with less “wet” days in a month.

Pressure is likely to be above normal across the UK, especially the north but less so in the south.

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 2018  (September October November) early indications. 

Milder than normal for the season as a whole and possibly each month individually but trending to smaller anomalies/nearer normal temperatures for November.

Rainfall near normal for the season but with a drier than average September and parts of October followed by a much wetter period into 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 2018/9  (December January and February) limited data from 4 models. 

Temperature probably near or above normal in December, much milder than average in January but possibly near or below normal in February – making he season as a whole near average or slightly above.

Wetter than average winter chiefly due to wetter December and January and  despite below normal precipitation in February. Below average snowfall, though slightly increased risk during February compared to normal.

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  www.weatherservice.co.uk

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.