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.

180419ssta

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.

tna0419

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.

nino0419

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.

noa0419

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.

tempsummary

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.

rainfall

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.

riverflow

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.

reslevel14

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.

Glofas0419

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.

npole0419

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.

strat0419

A 2: Upper Troposphere

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

z2000419

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.

mjjsum0419

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).

MtoAugE3

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

NMME140419JJA

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.

NMME0419MJJA

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

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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.

140319sst

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.

150319tropatl

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

140319ninot

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.

150319nao

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.temp150319

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.

climrain1503

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.

river1503

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.

resevoit1503

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.

150319glofas

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.  30hpaRecent 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.

50hpa

A 2: Upper Troposphere

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

150319cfs200Z

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.

1503ECj

ECMWF monthly

CFS2E30319

CFS2 E3 monthly

NMME0319

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.

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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.210219sst

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.

tna_anom_20190201

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

nino

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.

nao

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).oct-jan

 

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

raintempclimat

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

juntojanriverflow

ground

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.

17219res

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.

glofas

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.

sswend040219

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

hattardzonal

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.

strat10and50

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

10hpacfs2

A 2: Upper Troposphere

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

cfs2200mam

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.

cfs2e30219jja200hpa

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.

wmomulti0219mam

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

ukmo0219mam

UKMO Spring 2019 (MAM and monthly anomalies)

nmme0219mam

NMME multi model ensemble

cfs2e3mam0219

CFSv2 mean of 10 days output(E3 data)

ec0219mam

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

nmmeJJA0219

NMME multi model ensemble JJA monthly anomalies

cfs2e30219jja

CFSv2 E3 mean of 10 days runs. Monthly anomalies JJA

ECJJA022019

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.

170119ssta

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).

tna_anom_20190101

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.

nino0119

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.

180119nao

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.

180118612clim

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

 

180119climrecentt

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

180119climrecent

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..

180119riverground

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.

reslevel180118

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.

180119glofas

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.

180118stratalert

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,

180119strat

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

u_65n_10hpa

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.

cfs2ssw10

A 2: Upper Troposphere

z200fmam0119

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.

130119t2mcombined

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

130119ppncombined

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

B2: NMME data 8th Jan 2019

nmmefmam0119

B3: ECMWF 14th January ecfmam0119

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

e3fmam0119

Second version on the 12th of Jan

e3fmam0119jan12th

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.

160119cfs2

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.

nmmejja0119

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.

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.

181018sst

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.

tna_anom_20181001

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,

elninonormal

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.

NOA

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.

HSRA0918

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.

sm1018

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 

river

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.

res

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.

glofas

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.

30hpa

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.

z200DJF1018

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.

z200MAM1018

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.

CFS2e3djf102018

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

nmmedjf102018

NMME.  Top temperature anomaly Lower precipitation rate indication.

ECDJF102018

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.

nmmemam102018

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.

130918sstAnom

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.

tropsst

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).

tropsst1

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.

elninonormal

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.

naosep2018

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.

clim09

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.

09smchange

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 

08riverflows

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

resevoir

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.

SEP2018glofas

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.

ecmwf30a12

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.

z200DJF0918

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).

E3DJF0918

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

NMMEDJF0918

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

ECDJF092018

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.

SST00818

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.

SST10818

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

SST20818

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.

elninonormal

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.

NAO0818

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.

clim0818

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.

soilm0818

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 

rivground10818

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.

z200SON0818

CFS2 200hPa month mean and anomaly September to November 2018

z200DJF0818

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.

NNMESON0818

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

E3SON0818

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

ECSON082018

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.

NNMEDJF0818

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

E3DJF0818

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

ECDJF082018

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.