Experimental Long Range Forecast for SW England. October 2017 issue.

Published 17 October 2017.

1. Influences.

Changes in sea temperature.

anomnight.10.12.2017

The colder sea temperature anomalies to the SW of the UK have gone although the recent Extra Tropical Ophelia may have caused some cooling/up welling since the image date although this was not evident on an image for the 16th (not shown). Some relative cooling can be seen in the eastern Caribbean but in general the tropical North Atlantic is above normal and expected to remain warmer than normal (see image below). La Nina is evident in the Pacific and forecast to remain as a weak La Nina through to Spring 2018.

 

nino102017

NMME Nino3.4 forecast left. UKMO tropical North Atlantic forecast right.

ninoNAO

CFS Nino 3.4 forecast left. Observed NAO index right.

The North Atlantic Oscillation index (shown by a 500hPa index in the image above) turned positive fairly early in October after a negative phase in September. Weak indication at present for a milder/wetter winter season. For more information see Met Office NAO information.

La Nino conditions counter this to some extent with the IRI statistical relationship between La Nina and UK rainfall for the winter shown below. La Nina is weak so influence may not be strong.

La Nina

Winter season probabilities for Dry/Normal/We based on La Nina occurring 

Analysis and Numerical (model) output.

A: Rainfall during September was above normal across SW England, especially parts of S and SW Devon and S and E Cornwall, in terms of both measured rain and the number of wet days. Parts of Somerset and Dorset though were near normal or even a bit below.

Recent reservoir water levels remain above normal for the time of year. River flows and groundwater in the region are available from the Hydrological Summary  –  September 2017 summary PDF

Sunshine was again below normal during September and the temperature was near or even a little cooler than the 1981 to 2010 averaging periods but near normal when compared to the 1961 to 1990 period. The last generally warmer than average month being June 2017.

B: Upper Troposphere:

Average monthly 200hPa heights are again forecast to be above normal right through until February 2018 in the CFS2 data although increased zonal flow is also indicated January and February. Possibly suggesting low pressure tracks over the central or south of the UK during February rather than over or to the north as in January. Hint of more northerly flows in December?

z200

CFS2 200hPa heights (top) and anomalies (lower) November 2017 to February 2018

C: Lower Troposphere:

Temperature anomalies have been consistent in suggesting above normal temperatures in most model output, see NMME and CFS2 images below as example. Recently anomalies have been slightly warm so perhaps for November and December in SW England temperature may be nearer normal.

NMME102017

NMME Temperature anomaly (top). Rain rate anomaly (lower). November 2017 to February 2018

Rainfall forecasts are more variable in model output as can be seen by comparing NMME above and CFS2 below. There is also little if any consistency run to run. The main signal seems to be for above normal rain during the winter season but with some months possibly near or below normal made up for by wetter months.

E3DJF

CFS2  Temperature anomaly (top). Rain rate anomaly (lower). November 2017 to February 2018

D: Comment:  Seasonal temperature and rainfall forecast data have been poor recently, which is consistent with the data from 2016 which showed poor results for output issued during August and September. Rainfall forecasts were especially poor. Verification summary.

2. Forecast.

Remainder of Autumn  2017  (November) :

Temperature and rainfall are likely to average out to near or perhaps slightly above the long term average for SW England, although there is a chance that some eastern areas may be drier than normal.

November Climate: 1981 to 2010 November average mean temperature 8 or 9°C but nearer 6°C in upland areas. Maximum temperatures average 11 or 12°C but lower in upland areas. Average 1981 to 2010 rain 80 to 100mm to lee of Exmoor and Dartmoor (as low as 60mm over parts of Somerset) but  in western areas 100 to 200mm is fairly typical with over 250mm over the tops of the moors. 

Winter (2017 December, 2018  January and February) :

There is a strong indication for a mild winter in the SW of England which continues to be signalled by almost all model output. This does not rule out some colder spells but suggests that they will be short lived.  There is a suggestion that temperature anomalies could be lower early in the winter and higher later which hints at the temperature in December being nearer normal but with relatively milder months to follow.

Rainfall is uncertain month to month but the main theme of a wetter than normal winter seems to be consistent although December may be less wet. The snow risk is reduced compared to average with little if any snow for lower ground but some snow 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; 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 (2018 March April and May)  limted data:

Temperature probably near or slightly above normal for the season. Rainfall near or a little below normal at least in parts of the region.

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 and brief verification of previous Long Range Forecast summaries can be seen at   http://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

Advertisements

Experimental Long Range Forecast for SW England. September 2017 issue.

Published 19 September 2017.

1. Influences.

Changes in sea temperature.

anomnight.9.18.2017

The Atlantic to the W of the UK changed to a positive anomaly for a time but the colder area to the SW has expanded probably due to recent strong winds in this area. Overall, as can be seen in the graphic above, much of the Atlantic remains above normal for the time of year. In the Pacific conditions are moving towards La Nina as illustrated by the NMME forecast graphic below.

Statistically (according to IRI) La Nina conditions might imply near normal rainfall over much of UK in the winter period (Dec to Feb) but with the NW being wetter and the S possibly drier. The La Nina may not be strong enough for this effect to be noticeable.

SSTNINO

Left: NMME forecast for sea temperature in the Nino 3.4 region. Right: Tropical north Atlantic forecast sea temperature UKMO

AO

The North Atlantic Oscillation index (shown by a 500hPa index in the image above) turned positive in June and more or less remained in a positive phase until the third week in July before reverting to a negative phase which remains the dominant phase in the latest analysis. See Met Office NAO information.

Analysis and Numerical (model) output.

A: Rainfall during August was near or perhaps slightly above normal across much of SW England, in terms of measured rain, and together with the higher totals in June and July this has made up for the deficit from previous months.  The number of “dry” days was near or a little above normal for August but for the summer period as a whole was close to the average despite well above normal rain totals. This adds to the evidence for rain events to be “heavier” when they occur rather than there being more “wet” days.

Recent reservoir water levels have recovered and are now well above normal for the summer months. River flows and groundwater in the region should be available from the Hydrological Summary (Web says it has been published but pdf file was missing as of 19 Sept2017) –  August 2017 summary PDF

Sunshine was below normal for the summer despite temperatures being near or slightly above normal – largely due to warmer June offsetting near normal or cooler values in July and August.

B: Upper Troposphere:

Average monthly 200hPa heights are forecast to be above normal right through until February in the CFS 2 data although increased zonal flow is also indicated later in the Winter period which is somewhat later than earlier forecast output.

z2001

CFS2 200hPa height and anomaly Oct Nov Dec 2017

z200DJF

CFS2 200 hPa mean and anomaly Dec 2017 Jan and Feb 2018

C: Lower Troposphere:

NMME data continues to indicate strong positive temperature anomalies into Autumn and through Winter, although October and November values are nearer normal in SW England possibly due to the cooler than average sea temperatures just west of the UK. There remains strong agreement between most available models that temperatures will be above average through winter. Note rainfall anomaly is indicated in the form of an index for above (oranges) or below (blues) based on daily rain rates average over a month.

NMME1

NMME Temperature anomaly and rainfall index October and November 2017

NMMEDJF

NMME Temperature anomaly forecast and rainfall index. Dec 2017 to Feb 2018

D: Comment: 2016 Seasonal forecast rainfall data available in August and September were generally poor and the 2017 output for Summer 2017 were also quite poor.  Temperatures were generally better forecast although for the summer months there seems to be a warm bias in many models. Verification summary October to December last year.

2. Forecast.

Remainder of Autumn  2017  (October and November) :

Temperatures are likely to be near or perhaps slightly above normal perhaps with November seeing slightly higher positive anomalies than October.

Rainfall probably near normal, perhaps a little below normal in October and hence slightly above normal in November although month to month detail lacks consistency  between model output .

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 (2017 December, 2018  January and February) :

A mild or very mild winter continues to be indicated by almost all model output. This does not rule out some colder spells but suggest they will be short lived. Individual station plots indicate brief cold snaps in late December and in the first half of January although this detail is unlikely to be reliable.

Probably windier than a typical winter with near normal rainfall in the S and E of the Region but probably above normal in the N and W of the Region. Snow risk reduced compared to average, mainly in late December or first hale of January then little if any snow, except perhaps 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 (2018 March April and May)  limted data:

Temperature probably above normal for the season with rainfall near or a little below normal although some agreement that April could be 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.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary and brief verification of previous Long Range Forecast summaries can be seen at   http://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

 

 

Experimental Long Range Forecast for SW England. August 2017 issue.

Published 20 August 2017.

1. Influences.

Changes in sea temperature.

anomnight.8.17.2017

East and Central parts of the North Atlantic have cooled or remain cooler than normal but Northern and Western parts are now significantly above normal. In the short term winds from the NW may result in cooler than normal temperatures but longer term the potential rise in temperatures hints at a mild Autumn and perhaps Winter.

El Nino is expected to remain in a neutral phase as shown in the CFS2 and NMME ensemble forecast below. A developing  El Nino typically acts to reduce Atlantic Hurricanes hence this effect is not likely for the coming season although the Atlantic season has been a bit slow to develop so far.

nino0817

Tropical Atlantic temperatures are above normal as shown by the UKMO graphic below and the North Atlantic Oscillation (shown by a 500hPa index in the image below) turned positive in June and more or less remained in a positive phase until the third week in July before reverting to a negative phase. See Met Office NAO information.

trop

Analysis and Numerical (model) output.

A: Rainfall during June and July was above normal across much of SW England, in terms of total rain, and this has mostly made up for the deficit from previous months except perhaps in some eastern parts of the region. Interestingly the number of “dry” days was close to the average adding to the evidence for rain events to be “heavier” when they occur which may be linked to global warming as temperatures despite the rain have been normal or above.

Recent reservoir water levels although slightly below average, have recovered. River flows and groundwater in the region show mixed results with moorland rivers showing increased flow as can be seen in the Hydrological Summary –  July 2017 summary PDF

Riverflows

B: Upper Troposphere:

Average monthly 200hPa heights are forecast to be above normal right through until February in the CFS 2 data although increased zonal flow is also indicated later in the Autumn and into to Winter period.

z200SON0817

CFS2 200hPa height month mean and anomaly September to November 2017

z200DJF0817

CFS2 200hPa month means height and anomaly December 2017 to February 2018

C: Lower Troposphere:

NMME data continues to indicate strong positive temperature anomalies into Autumn and through Winter, although September values are near normal in SW England in the latest NMME forecast possibly due to the cooler than average sea temperatures just west of the UK. There remains strong agreement between most available models that temperatures will be above average through winter.

SONT

NMME Sep to Nov 2017 temperature anomaly

DJFT

NMME temperature anomaly December 2017 to February 2018

Forecasts of precipitation issued based on August data have a low success rate compared to the temperature anomalies. That said there is a signal for a wetter than normal winter period with the main uncertainty in the Autumn.

sonP

NMME precipitation anomaly for September to November 2017

djfP

NMME precipitation anomaly December 2017 to February 2018

cap

Combined ECMWF/UKMO/Meteo France. Temperature and Rainfall Tercile summary September to November 2017. 

 

2. Forecast.

 

Autumn  2017  (September, October and November) :

There remains a consistent indication for a warmer/milder than normal season. Possibly well above normal in October but perhaps close to normal in September.

Rainfall probably near normal or a little below normal for the season but the month to month detail is inconsistent and at least one month may be see above normal rain. The trend is for increasing rainfall rates later in the Autumn.

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 (2017 December, 2018  January and February) :

A mild or very mild winter is likely which does not rule out some colder spells. Individual station plots indicate brief cold snaps around the turn of the year and perhaps in February.

Probably windier than typical and rainfall is likely to be above normal for the season. Snow risk reduced compared to average, mainly in late December then little if any snow, except perhaps 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 (2018 March April and May)  very limted data:

Average temperature probably above normal for the season and rainfall near or a little below normal.

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 and brief verification of previous Long Range Forecast summaries can be seen at   http://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

 

 

Experimental Long Range Forecast for SW England. July 2017 issue.

Published 17 July 2017.

1. Influences.

Changes in sea temperature.

anomnight.7.13.2017

The sea temperature remains warmer than average near and to the southwest of the UK as well as in the Mediterranean. Much of the North Atlantic remains below average and this colder area has extended towards Ireland.  The colder North Atlantic sea temperatures increases the risk of cooler temperatures this summer with winds from the West or NW but winds from other directions flow over warmer than normal seas.

El Nino is expected to remain in a neutral phase as shown in the CFS2 and NMME ensemble forecast below. A developing  El Nino typically acts to reduce Atlantic Hurricanes hence this effect is not likely for the coming season.

nino3.4

Tropical Atlantic temperatures are above normal as shown by the UKMO graphic below and the North Atlantic Oscillation (shown by a 500hPa index in the image below) turned positive in June and has more or less remained in a positive phase. See Met Office NAO information.

NATL

Analysis and Numerical (model) output.

A: Rainfall during June was above normal across much of SW England but this has not made up for the deficit from previous months.

rainfall

In addition most of the rain in June fell on just two days and reservoir water levels remain below average. River flows and groundwater in the region show mixed results with moorland rivers showing increased flow as can be seen in the Hydrological Summary –  June 2017 summary PDF

res

SW Water Resevoir Levels

B: Upper Troposphere:

There is some agreement between models that pressure in the south of England may be above average through the Autumn. Average monthly 200hPa heights are forecast to be above normal right through until February in the CFS 2 data.

z200SAON0717

CFS2 mean monthly 200hPa heights and anomaly August to November

z200DJF0717

CFS2 mean monthly 200hPa heights and anomaly December to February

C: Lower Troposphere:

NMME data continues to indicate strong positive temperature anomalies through the remainder of summer, into Autumn and through winter. There is good agreement between most available models that temperatures will be above average through winter.

Autumn

August to November NMME monthly temperature anomaly (upper row) and (lower row) rainfall rate indication for below in blue or above in orange 

Copernicus and CFS2 three month means differ in the temperature anomaly and rainfall but this may be due to smaller anomalies during this period.

soncomp

Rainfall forecasts are the least reliable (as shown in the verification section below) but the strongest anomalies for the Autumn are in September and October. For the winter there is a strong signal for an unusually mild and wet season across much of the UK.

winter

NMME temperature and rainfall anomaly forecast for Dec 2017 to Feb 2018

Verification. Recent results June 2017.

NMMEPPN

The image above shows June rainfall anomalies based on forecast data available in March April and May and the associated observed anomalies (right) in CPC and Met Office data. The most recent 3 month verification is available at this link.

2. Forecast.

Remainder of Summer 2017  (August):

Above normal temperatures are most likely though perhaps not averaging out with a large anomaly. There is a chance that Easterly winds may be more frequent than normal, due to higher than normal pressure over the UK. Probably drier than normal, reduced number of wet days if not rain total. Rain total may be modified by shower/thunderstorm risk which can bring locally high rain totals but not for the whole region.

August 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. Average 1981 to 2010 rain 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  2017  (September, October and November) :

There remains a consistent indication for a warmer/milder than normal season. Possibly well above normal in October but perhaps only slightly above normal in other months.

Rainfall probably near normal or a little below normal for the season but the month to month detail is inconsistent and at least one month may be see above normal rain. The trend is for increasing rainfall later in the Autumn.

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 (2017 December, 2018  January and February)  –  limited data:

A mild or very mild winter is likely which does not rule out some colder spells. Individual station plots indicate brief cold snaps in late December and again in January and February. February may be slightly less mild than the other months, compared to average.

Probably windier than typical and rainfall is likely to be above normal for the season. Snow risk reduced compared to average, mainly in late December then little if any snow, except perhaps 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.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary and brief verification of previous Long Range Forecast summaries can be seen at   http://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

 

Experimental Long Range Forecast for SW England. June 2017 issue.

Published 20 June 2017.

1. Influences.

Changes in sea temperature.

anomnight.6.19.2017

Sea temperature anomaly 19 June 2017

The sea temperature has warmed near and to the southwest of the UK as well as in the Mediterranean. Much of the North Atlantic has cooled, probably due to mixing of the surface layers due to large deep low pressure areas during June as shown in the composite of analysis for June to date. The colder North Atlantic sea temperatures increases the risk of cooler temperatures this summer with winds from the NW but winds from other directions flow over warmer than normal seas.

anal

Analysis 1 to 20 June Midnight UTC

The risk of a developing El Nino looks to have reduced as shown by the CFS SST forecast for Nino 3.4 location in the Pacific. El Nino typically acts to reduce Atlantic Hurricanes hence this effect is not likely for the coming season. Tropical Atlantic temperatures are above normal as shown by the UKMO graphic below.

TropicalSST

The North Atlantic Oscillation (shown by a 500hPa index in the image below) went negative during May but has since return to a positive phase. See Met Office NAO information.

NAO200617

 

Analysis and Numerical (model) output.

A: Rainfall during May was again below normal across much of SW England but not everywhere with parts of south Devon not far from normal. River flows and groundwater in the region are below normal – for more details, see the Hydrological Summary –  May 2017 summary PDF

June so far has seen rather mixed rainfall with period of heavy rain in the first third of the month followed by a dry period around the middle of the month and what looks like a wetter end to June. Following a “dry” winter and Spring reservoir levels remain below normal for the time of year and also below the 1995 drought levels. Water storage is much greater than during the 1980’s when significant water saving measures came into play and there has been a slight reduction in the deficit early in June.  For reservoir details see SW Water web site.

B: Upper Troposphere:

200hPa heights are forecast to be above normal although in August the NCAR anomaly suggest at least some risk of more troughing.

z200JULAUG

200hpa  CFS2 July and August mean and anomaly with lower images being the NCAR anomaly.

For the Autumn above normal heights continue to be forecast at 200hPa

CFS2z200SPN0617

September to November 200hPa mean and anomaly. Lower images NCAR anomaly.

C: Lower Troposphere:

NMME data continues to indicate strong positive temperature anomalies through the remainder of summer and into Autumn

JA0617

NMME June data. Top Temperature mean anomaly July and August. Bottom row indicator for below (blue) or above (orange) normal rain rate anomaly.

SON0617

NMME June data. Top Temperature mean anomaly September to November. Bottom row indicator for below (blue) or above (orange) normal rain rate anomaly.

Although all models agree on normal or above normal temperatures (mostly forecast above), for the summer and autumn, rainfall predictions are not so reliable.

NMME data suggest wetter periods for SW England in September and perhaps in November but overall indicates a continuation of the drier than normal types. A note of caution is required because model resolutions prevent the forecasting of smaller scale rainfall for example showers and thunderstorms. Consequently the drier types may be indicative of less wet days in a month rather than total rainfall. The sample CFS2 shown below indicates a wetter October in the SW for example.

CFSPPN

Verification. Recent results Spring 2017.

Models overall had a good idea that temperature would be above normal but rainfall forecasts where not good with little signal for a very dry April and May which was wetter in the SE third of UK but drier elsewhere. An example of  forecast reliability is shown below with the March April and May temperature and rainfall anomalies compared to the Copernicus multi model ensemble forecast based on data in February 2017 data.

mamcap

Spring temperature (top) and rainfall (lower) anomaly forecast from Feb 2017 data compared with observed anomalies.

 

2. Forecast.

Remainder of Summer 2017  (July and August):

Above normal temperatures are most likely and possibly well above normal values. There is a risk that Easterly winds may be more frequent than normal, due to higher than normal pressure over and to the north of the UK.

After and unsettled start to July probably becoming drier than average in terms of number of dry days and possibly also rain total. August may be also drier than normal but perhaps modified by shower/thunderstorm risk which can bring locally high rain totals but not for the whole region.

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

Autumn  2017  (September, October and November) :

Consistent indication for a warmer/milder than normal season. Possibly well above normal for September and October but perhaps less so in November.

Rainfall probably near normal overall but above normal in September and perhaps November. October probably near or below normal rainfall.

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 (2017 December, 2018  January and February)  – very limited data:

December probably near normal although hints at a colder spell late in the month. January and February milder than normal, hence overall a milder than normal winter.

Probably windier than typical and rainfall is likely to be above normal for the season. Snow risk mainly late December then little if any snow, except perhaps 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.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary and brief verification of previous Long Range Forecast summaries can be seen at   http://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

 

 

 

Experimental Long Range Forecast for SW England. May 2017 issue.

Published 17 May 2017.

1. Influences.

Changes in sea temperature.

anomnight.5.15.2017

The Sea Temperature Anomaly (above) shows further cooling in western parts of the North Atlantic and little change in the warmer than average area in the East Pacific. The North Sea, Biscay and northern Mediterranean areas look to be a little cooler than average for mid May.

El Nino 3.4 predictions suggest a slight strengthening as shown by the NMME and CFS2 forecast plots below, although CFS2 has been trending nearer normal but with a large spread in solutions

nino34.rescaling.ENSMEANnino34Mon

The influence of an El Nino has on rainfall in the SW of the UK according the statistical output produced by IRI is such that there is an increased probability of near normal summer rainfall for the N and W of the Region but less impact in the S and E.

The North Atlantic Oscillation (shown by a 500hPa index in the image below) has gone negative during May. Should this be maintained then this might imply a drier and warmer summer for the UK. See Met Office NAO information.

nao.mrf.obs

Analysis and Numerical (model) output.

A: Rainfall during April was unusually low across much of SW England – for details see the Hydrological Summary –  April 2017 summary PDF

There was some very heavy rain for two days spanning the end of April and start of May across parts of S Devon and W Dorset. Depending on whether rainfall measurement period 00-24 or the standard UK climate period of 0900-0900 is used half the rain total was either included in the May or in the latter case the April rainfall figures. Since then, following a dry week or so, May has become wetter. Following a “dry” winter reservoir levels remain below normal for the time of year and also below the 1995 drought levels. Water storage is much greater than during the 1980’s when significant water saving measures came into play.  For reservoir details see SW Water web site.

B: Upper Troposphere:

NMME 200hPa ensemble mean was not available. Looking at four of the available models there was agreement in that heights would be mostly above normal in July and possibly other summer months and that an enhanced SW jet was likely in November near UK and between 40 and 50 deg North across the Atlantic.

Z200CFS2JJA0517

CFS2 200hPa mean height (top row) and anomaly (lower row) for June to August

Taken together 3 out of 5 of the models in the NMME grouping suggest above normal heights for the June to October period.

Z200CFS2SON0517

CFS2 200hPa mean height and anomaly September to November

Looking at data from the Copernicus ensemble system for 500hPa height anomalies there is a strong signal for above normal heights this summer although Meteo France hints a lower heights near to the South of the Uk and more especially further south over France and the Mediterranean.

C: Lower Troposphere:

There is a very strong signal from most models for above normal temperatures during both Summer and Autumn, although Meteo France suggest coastal areas near E or SE facing coasts might well be cooler in June and given the cooler N Sea temperatures at present this may be correct for the early part of June. BCC China suggests that the next colder than average month might be December. The stronger anomaly in November probably linked to increased Atlantic mobility which shows up in the rainfall rate anomaly.

jja0517

June July and August 2017. NMME whole month temperature anomaly (top row) and  indication for above or below model normal rainfall (lower row).

In general rainfall anomalies are less well forecast and show bigger variations in detail between the models.  That said there is some agreement that July could be the drier month and November the wetter.

son0517

September October and November 2017. NMME whole month temperature anomaly (top row) and  indication for above or below model normal rainfall (lower row).

Verification. Recent results summary for 2017.

January to April 2017 models overall had a good idea that temperature would be above normal but rainfall forecasts where not especially good with little signal for a very dry April. UK area Seasonal Forecast Verification

 

2. Forecast.

 

Summer 2017  (June July August):

Above normal temperatures are most likely and possibly well above normal values. There is a risk that Easterly winds may be more frequent than normal, due to higher than normal pressure over and to the north of the UK. This may make some coastal areas exposed to the east wind cooler at times especially during early June until sea temperatures increase.

 

Rainfall, probably drier than average in terms of number of dry days and possibly also rain total. Uncertain as to which month might have the highest number of wet days but some  hints that June could be wetter at least for a time followed by a drier July and more mixed picture in August. Indication of lower pressure than normal over France and the South of the UK may imply increased risk of thunder showers during the summer leading to highly variable rainfall totals.

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  2017  (September, October and November) :

Consistent indication for a warmer than normal September with temperatures above normal throughout the season. Possibly well above normal in November, although this may be offset by stronger winds?

Rainfall in September and October probably near or below normal but followed by a wet November, so on balance ending up near normal for the Autumn 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 (2017 December, 2018  January and February)  – very limited data:

December may have colder than normal temperatures in places although the SW of England probably near normal. Returning to milder than normal for the remainder of winter.

Rainfall is likely to be above normal with little if any snow except perhaps 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.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary and brief verification of previous Long Range Forecast summaries can be seen at   http://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

 

 

 

Experimental Long Range Forecast for SW England. April 2017 issue.

Published 18 April 2017.

1. Potential influences.

Changes in sea temperature.

anomnight.4.17.2017

The Sea Temperature Anomaly (above) shows a little cooling in the western parts of the North Atlantic and an expansion of the warm area in the East Pacific. The Mediterranean and areas around Spain look to have increased warm anomalies.

El Nino predictions suggest a slight strengthening as shown by the NMME and CFS2 forecast plots below, although only a minority suggest a strong El Nino this summer.

nino04

Nino 3.4 Forecast. Left NMME 08Apr17 and Right CFS2 18Apr17.

The influence of an El Nino has on rainfall in the SW of the UK according the statistical output produced by IRI is such that there is an increased probability of near normal summer rainfall for the N and W of the Region but less impact in the S and E.

Analysis and Numerical (model) output.

A: Stratosphere:

The polar vortex has been completely warmed out as shown by the ECMWF 30hPa plot.

ecmwf30a12

B: Hydrological Summary – see March 2017 summary PDF

Due to higher rainfall in March river flows across SW England were near normal and in the north somewhat above normal. October 2016 to March 2017 rainfall was below normal and the groundwater levels in the SE of Devon and into Dorset were below normal. (Parts of this area relies on water extraction from underground sources). Reservoir levels in the SW Water area stand at about 87% of capacity which is about 10% below the level prior to  the summer 1995 drought levels. April to date has been a drier than normal month.

C: Troposphere:

Forecast data from CFS2 and NMME show above normal 200 hPa heights through the Summer and into Autumn suggesting reduced westerly jet winds compared to a typical year. Pressure may be higher than average during the May to October period.

cMJJA0417

May to August CFS2 200hPa monthly mean (top) NMME anomaly (middle) CFS2 anomaly (lower)

cSON0417

Sept to November 200hPa

 

D: Surface outlook.

There is good support from international seasonal model output (April 2017 data) for temperatures to be above normal as illustrated by the NMME temperature anomaly plots (shown below). BCC China hints at the next colder than normal month may be December although this is not supported by other models. There is no significant indication of a colder than normal summer but note that the models have not been good at picking out a colder month in a sequence of mild months.

MJJA

May to August NMME temperature mean anomaly (top) and rainfall rate indicator (below)

SON

September to November NMME temperature anomaly and rainfall indicator.

Rainfall has been less reliably forecast and forecasts are not consistent between models or between new runs of the same model. The developing El Nino statistically leans towards to near normal rainfall over at least parts of the SW through summer although the El Nino may not become strong enough to be sure of this relationship holding true.

NMME signals are quite weak for SW England suggesting a wetter June and possibly August although May could well start drier and cooler than normal. There is some support for November being the next “wet” month,

Verification Recent results summary for 2016.

Rough and ready assessment of temperature and rainfall from various models  three month seasonal forecasts.  Note how forecasts issued in November to April had better results than other months. The left hand column is the total out of a potential max score of 36.

Temp2016

Temperature. Most models gave favourably results over 50% of the time.

Precip2016

Rainfall. Fewer models got favourable results over 50% of the time. 

There are hints that multi model ensembles may detract from a single models better performance.

2. Forecast.

Remainder of Spring (2017 May) :

Temperature probably near normal in May after a colder than normal start, becoming milder than average later. Chilly nights may be compensated for by warm daytime sunshine.

Mixed rainfall signal but probably near normal although parts of South and East Devon, Somerset and Dorset may be drier than normal.

Climate: 1981-2010 average period. May mean temperature 11 or 12°C but a few degrees cooler over the moors.  Spring average rainfall 200 to 300mm lowest values in E Devon and over parts of Somerset,  May rainfall typically 60 to 80mm but as low as 40mm E of Moors and in Somerset and parts of Dorset and more than 100mm over the moors.

Summer 2017  (June July August):

Consistent indication for temperatures to be warmer than 1981 to 2010 average although some western coastal areas may be nearer normal. July may be further above average then August. Increased chance of well above normal temperatures (anomaly more than 1 deg C) during the period. There are no indications for a cooler than normal summer.

Rainfall, probably drier then average in terms of number of dry days and possibly also rain total. Uncertain as to which month might have the highest number of wet days but some  hints that June and August could be a little wetter than July but not by much.  Indication of lower pressure than normal over France and the South of the UK may imply increased risk of thunder showers in August leading to highly variable rainfall totals.

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  2017  (September, October and November) :

Warmer than normal especially in September with temperatures mostly above normal throughout the season.

September and October probably near or below normal rainfall but followed by a wet 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 and brief verification of previous Long Range Forecast summaries can be seen at   http://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