Experimental Long Range Forecast for SW England. March 2017.

Published 18 March 2017.

1. Potential influences.

Changes in sea temperature.

anomnight.3.16.2017

The Sea Temperature Anomaly (above) shows fairly small differences from previous anomaly charts. There looks to be some cooling, relative to average, in the Atlantic along 30 deg North and a little warming in the eastern Pacific near the equator which is consistent with the slow transition to El Nino conditions as shown in the graphic below.

nino34

Ensemble forecast for the Nino 3.4 area of the Pacific. Left NMME+IMME and Right CFSv2.

The influence 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 at 30hPa remains displaced with further weakening likely in the next couple of weeks, s shown by the ECMWF 30Hpa forcast below. Analysis by JMA shows N Pole Temperature above normal following the February Stratospheric Warming.

strat

B: Troposphere:

NMME 200hPa data was not available. CFS2 data continues to suggest above normal heights and hence reduced westerly Atlantic jet flow for the next several mouths. Note, however, that in August the anomaly is reduced over the UK area.

 

CFSz200

C: Hydrological Summary – see February 2017 summary PDF

River flows across SW England were only slightly below normal in February but for the Winter (Dec to Feb) flow were generally below normal and in the north of the region, exceptionally low. Rainfall for the winter was below normal and showed a return period of between 10 and 20 years. Looking at longer lead periods for example; Sept to Feb and March 2016 to Feb 2017, the return period for the recorded below average rainfall extends to as much as 25 years. According to South West Water reservoir storage is about 82 percent of normal  and is running below the drought level of 1995, although much depends on rainfall over the next few months as o whether this will have an impact on summer water availability. There is a lot more water storage available in the SW than during the 1980’s when there were significant water restrictions in places.

D: Surface outlook.

There is good support from international seasonal model output (March 2017 data) for temperatures to be above normal as illustrated by the NMME temperature anomaly plots below.  Rainfall is more problematic and there is much less agreement between the models with regards month to month and location specific detail. For example recent CFS2 data (output date 16th March) suggests SW of UK being drier in April and wetter in July. The drier weather in NMME output being a little further south over France in April, which is typical of the type of variability between models.

NMME0317

Some models indicate above normal sea level pressure over the UK during the next several months, although this becomes a weaker signal in the south of the UK for the summer with hints at lower pressure in the south and over France.

Recent results.

UK: Verification for the December 2016 to February 2017 period showed that the temperature for the season was a reasonably guide for the UK but precipitation was often over estimated. Looking back to Summer 2016 NMME forecast in March and May 2016 gave some good indication for drier types in the south of UK in July.

2. Forecast.

Remainder of Spring (2017 April and May) :

Average temperature probably above normal for both April and May although with the chance of periods of High Pressure could not rule out some chilly nights in April. In May perhaps only slightly above the long term average.

Rainfall probably near normal for the season, perhaps above normal in the more exposed western parts of the Southwest but below normal in parts of South and East Devon, parts of Somerset and into Dorset. There is a chance for above normal rainfall in all areas but rainfall tends to be over forecast in the models.

Climate: 1981-2010 average period. Spring mean temperature 9 or 10°C but a few degrees cooler over the moors. Roughly Apr 8 or 9°C  May 11 or 12°C. Spring average rainfall 200 to 300mm lowest values in E Devon and over parts of Somerset,  April  typically 60 to 80mm but in SW Devon and parts of Cornwall 80 to 100mm to as low as 40 mm East of the Moors also in Somerset and parts of Dorset to more than 100 mm over the moors. May 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 but 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. Fairly strong signal for July to be drier. Indications for lower pressure than normal over France and the South of the UK may imply increased risk of thunder showers with highly variable rainfall in August.

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) 2017 – limited data:

Possibly a drier and warmer start to Autumn then near normal or wetter with milder than normal temperatures.

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

 

Experimental Long Range Forecast for SW England. February 2017.

Published 17 February 2017.

1. Potential influences.

Changes in sea temperature.

anomnight-2-16-2017

Apart from some relative cooling in Biscay and around Spain and Portugal, the sea temperature anomaly in the North Atlantic is similar to those in mid January. The La Nina in the mid Pacific has decayed with the current neutral conditions likely to slowly return to a weak El Nino state during the 2017 summer. This transition can been seen in the CFS2 and NNME output shown below which is perhaps a little quicker and stronger indication than last months forecast.

Should an El Nino develop more quickly the influence on rainfall in the SW of the UK (according the statistical output IRI statistical output) 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:

A major stratospheric warming event took place in early February with a splitting of the Polar Vortex and a temporary reversal of the stratospheric wind in the UK area. Temperature at the North Pole rose sharply at 30hPa but has since returned to normal, as shown in the graphic below.

pole30_nh

Tokyo issued at major stratospheric warming start message on the 3rd and an end message on the 10th.

startstopstrat

Subsequently the western part of the vortex has declined with a new strong vortex developing to the north of Russia during the second half of February.

contstrat

It is not clear whether this will aid the development of high pressure to the west of the UK and more cyclonic patterns further east hence an increased risk of chilly NW types for the UK?

B: Troposphere:

200hPa CFS2 and NMME monthly mean anomalies hint at slightly stronger jet flow towards the S of UK in March but with above normal heights forecast to develop later in Spring.

z200mam0217

March April May 2017 CFS2 200hPa mean heights (top) anomaly (mid) and NMME anomaly (bottom row) Data 6FEB2017.

z200jja0217

June July August CFS2 mean heights anomaly and NMME anomaly

For the summer months positive anomalies continue but with differences between CFS2 and he other models making up the NMME group of ensembles.

C: Surface NMME output:

mam0217

NMME Mar Apr May temperature anomaly (top) Rainfall indication for above/below normal.

There is good support from the various seasonal models for above average temperature or at worst normal values. Rainfall patterns are less clear but other output does suggest a wetter March in the west.

jja0217

NMME Jun Jul Aug temperature and rainfall indication.

There is a consistent signal for above average temperature (up to plus 1 C anomaly) across the UK  the rainfall is less consistent but at least a hint of drier overall in places.

Recent results.

UK: Verification for the November 2016 to January period showed that the temperature for the season was a reasonably guide for the UK but month to month detail was unreliable. Precipitation detail is often poor mainly due to dry spells being under forecast.

SW England:

2. Forecast.

 

Spring (2017 March April and May) :

Average temperature probably above normal for the season. March less clear could be nearer normal, with chilly NW or N winds for periods although if rainfall correct then milder nights may tip the balance to above normal. April slightly above normal with May possibly the mildest relative to average values.

Rainfall probably near normal for the season, perhaps above normal in the more exposed western parts of the Southwest but below normal in parts of South and East Devon, parts of Somerset and into Dorset. March could be the wetter month of the three.

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 2017  (June July August):

Temperatures probably warmer than 1981 to 2010 average although some western coastal areas may be nearer normal. Rainfall, probably drier then average in terms of number of dry days and possibly also rain total. Drier types more especially for July and August perhaps after a wetter June. This is a change from last months forecast and may be unreliable.

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.

Early indication for Autumn  (September, October and November) 2017 – limited data:

 

Possibly a drier and warmer start to Autumn then near normal or wetter with near normal temperatures.

(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

Experimental Long Range Forecast for SW England. January 2017.

Published 18 January 2017.

1. Potential influences.

Changes in sea temperature.

anomnight-1-16-2017

Sea temperature anomalies are very similar to a month ago with areas of above normal near to the UK and a similar area of below normal in the North Atlantic. In the Pacific the weak La Nina continues to weaken with essentially neutral conditions over the next several months, possibly trending to weak El Nino conditions late in 2017. This is illustrated by the CFS2 and NMME ENSO 3.4 area forecast sea temperature shown below.

nino34mon

Numerical (model) output.

A: Stratosphere:

The North Polar Vortex was slow to establish during the early winter but is now well established with temperatures low enough for Ozone reduction. Zonal 50hPa and Polar 30hPa temperature plots are shown below.

50mbnhlopole30_nh

Ozone shows at least a reduction of 20% in the polar vortex area although this area remains out of sunlight for now.

current

Areas of stratospheric warming developing across the Pacific are likely to lead the polar vortex being disturbed. Consequently the colder temperatures in the polar vortex may relocate and not persist resulting in a recovery in Ozone values.

ecmwf50a12

The 50hPa analysis 17th Jan 1200UTC shows the strong polar vortex and the forecast sequence suggests a relocation of the vortex and perhaps the start of conditions favourable to more blocked surface patterns for the start of February. The evolution of the polar vortex/stratospheric warming will need to be watched to see if moves to a pattern more conducive to blocked surface patterns for the UK area due and a reversal of the stratospheric flow.

B: Troposphere:

The NMME 200hPa output suggest above normal heights over the UK in the period February to August 2017 but there is also a suggestion of enhanced jet flows across parts of the N Atlantic steering low pressure towards or to the North of the UK. Consequently a winter blocked pattern may be in the wrong place to bring significantly colder temperatures to the UK for the last part of Winter/Early Spring.

z200fmam0117

NMME 200hPa anomalies with (lower row) CFS2 mean and anomaly Feb to May 2017

z200jja0117

As above but for the period June to August 2017

C: Surface NMME output:

nmmefmam0117

NMME month mean anomaly. February to May 2017. Top row temperature. Lower row indication of above (oranges) or below (blues) model normal rainfall rates.

nmmejja0117

NMME data as above but for period June to August 2017.

Model output (as available between 1st and 18th January) mostly agrees with the idea of above normal temperatures (as shown in the graphics above) although, in February, the outcome for the S of the UK is perhaps less clear cut with NASA data hinting at a colder and CFS2 suggesting near normal. Rainfall is always more problematic because rainfall is often about mean rain rates and short periods of heavy rain not likely to be captured, hence sometimes drier than normal might mean less rain days rather than lower rainfall totals.

Recent results.

Verification for the October to December 2016 period showed that seasonal model rainfall output was quite misleading, partly due to the poor prediction of blocking High Pressure and associated dry weather. Consequently given the risk of a stratospheric warming event leading to increased chance of blocking there may also be an increased chance of drier and colder weather for a time in February or March.

The first half of winter has been drier and milder than average with below average sunshine (cloudier skies) but above average pressure. This is probably unusual because dry weather and high pressure in winter is more likely to lead to colder than milder temperatures.

2. Forecast.

Remainder of Winter ( 2017 February) :

The mean temperature in February is most likely to be near or above the longer term average with less frequent frosts. The early part of the month is most likely to be mild, though with a risk of colder spells later. Despite higher than average pressure winds may often be from between West and South suggesting rather cloudy skies.

Rainfall probably near or below normal at least during the first half of the month. The snow risk remains lower than average which means some snow accumulation over the moors but not much elsewhere.

February climate: Temperature 1981-2010  typical mean 5 or 6°C but over 6°C in West Cornwall and only 2 or 3°C over the higher ground). Rainfall: 60 to 80mm to lee of moors, but 40 to 60mm over parts of Somerset. 80 to 100 elsewhere but higher totals over parts of Cornwall and NW Devon but over 200mm  over the higher moors). Snow climatology  many low lying areas less than 1 Day on average, hills 1 to 4 days but tops of moors 4 to 10 days. One in three years have no lying snow.

Spring (2017 March April and May) :

Mean temperatures probably above normal for the season, as well as for each individual month. March may well be relatively milder (stronger anomaly) than April or May which could be closer to normal. Rainfall probably near normal for the season, perhaps above normal in the more exposed western parts of the Southwest but below normal in parts of South and East Devon, parts of Somerset and into Dorset. March could be the “wetter” month of the three.

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 2017  (June July August):

Slightly warmer than average summer temperatures although some western areas may be nearer normal due to more frequent west winds. Rainfall, probably drier then average in terms of number of dry days if not the rain totals. Drier types more especially for June and July rather than August. Note a drier June and/or July and wetter August is not unusual.

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 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. December 2016 issue.

Published 18 December 2016.

1. Potential influences.

Changes in sea temperature.

anomnight-12-15-2016

The temperature of the sea around the UK remains slightly above the seasonal norm with the pattern of slightly cooler temperatures SE of Greenland and SW of Iceland being very similar to mid November.

decnino

ENSO 3.4 Early December probability plot and Mid December model comparison. 

The weak El Nina is expected to become neutral and then in late summer trend towards another El Nino. Consequently any statistical relationship between ENSO conditions and rainfall becomes even more uncertain by Spring.

The IRI produced graphic for January to March rainfall probability during La Nina (shown below) suggests near normal totals but hints at wetter in the NW of the UK and drier in East of England

jfmnina

Rainfall probability for dry/normal/wet during La Nina January to March

Numerical (model) output.

Most of the model output for the Jan to March period also implies near normal rainfall but with a chance of above normal in more northwestern parts and less than average in the South or East of the UK. (Text based summary of model output for the UK and Eire). Much like the CFS2 output in November the data from mid month suggests a drier than normal January, suggesting that February or March might well be wetter in order to get a near or above normal season average.

NMME data illustrates this quite well with mean rain rates (shown on the lower part of the graphic) showing below model norms in Jan and Feb then above normal March to May. February has the least positive temperature anomaly being not far from normal.

nmmejfm1216

NMME: Top row – temperature anomaly (+/-1C). Lower row – rainfall rate indicative anomaly blue below and orange above average rain rates

Rain rate anomalies might reflect the intensity or the number of rain days but implies a wetter Spring for many. Skill in the output for Autumn was not good – see verification Autumn 2016.

NMME 200hPa mean values not available but the CFS2 mean and anomalies (below) imply developing enhanced jet/zonal flow for part of February and more especially for March.This replaces higher heights shown in January. Above normal heights are also evident in the forecast for April and May.

z200dec2016comps

CFS2 data from 8th December 2016. 200hPa  January to May. On top row month mean heights and on lower row the month mean anomaly.


2. Forecast.

Remainder of Winter ( 2017  January and February) :

 

Temperatures in early January may be colder than average followed by a recovery to milder weather and then near normal values in February. This means at least some frost, especially early in the period, although the overall temperature for Winter (Dec to Feb) may well be near or milder than the long term 1981 to 2010 average.

Rainfall may also be lower than average in January, especially the early part of the month, before returning to near average rainfall figures. The snow risk remains lower than average which means some snow accumulation over the moors but not much elsewhere.

 

Winter climate: 1981-2010 average temperature values for lowland areas 7°C in the West and 5°C in the East. (Jan and Feb similar to season values) 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. (Jan 60 to 100mm to lee of moors, 100 to 200mm elsewhere but higher totals over the moors. February, slightly lower values than in January)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 (2017 March April and May) :

 

Above average temperatures are most likely for the season, as well as for each individual month. Rainfall probably near normal but perhaps above in the more exposed western parts of the Southwest but less likely in places to the East of the Moors, e.g: in parts of South and East Devon due to pressure being higher than normal in the south of England

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 2017  limited data (June July August):

Warmer than average summer temperatures with below average rainfall  in terms of number of dry days if not the rain totals. Drier types more especially for June and July rather than August. Note a drier June and/or July and wetter August is not unusual.

Summer climate: 1981 to 2010 average 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 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. November 2016 issue.

Published 18 November 2016.

1. Potential influences.

Changes in sea temperature.

anomnight-11-17-2016

The sea temperature around the UK remains above normal and the colder anomaly in the North Atlantic is similar to last month. In the Pacific a large colder than normal area has developed and the La Nina remains fairly week. The La Nina is expected to weaken further during the course of the winter months as shown by the consensus probability forecast below.

nino

ENSO 3.4 Comparison Forecast and Probability plot

The probability plot above suggests a move to Neutral ENSO conditions later in the winter. Until then the statistical relationship between La Nina and UK precipitation may be worth a look, especially as there is support in some climate model output for a drier December (eg: NMME CFS  BCC China Cansips).

DJFnina

Probability for Dry Wet Normal precipitation during La Nina

Numerical (model) output.

CFS ten day mean ensemble precipitation output for December has moved towards a drier forecast, as shown below. Despite this change there remains a weak signal for a wetter than normal winter across parts of SW England in the CFS output.

cfs

There is also a corresponding change in the temperatures with a less mild forecast for December and January made up for by a milder February. At the time of writing almost all the available seasonal models predict a normal to mild winter for SW England.

NMME data also shows variation in the precipitation but is fairly consistent with an above normal temperature forecast.

nmmedjf

NMME Winter (DJF) forecast temperature anomaly (top) and precipitation anomaly indicator for below (blue) and above (orange) ensemble model normal

nmmemam

NMME Spring (MAM)

CFS (200hPa) upper wind forecast mean and anomaly suggests enhanced jet over Canada, extending at times across the Atlantic towards UK. This implies stronger Atlantic low pressure systems during the January to March period. Later model runs appear to have maintained a stronger than normal jet.

z200com

CFS2 December to March 200hPa monthly mean height (top) and anomaly

2. Forecast.

Winter (2016 December, 2017  January and February) :

Temperatures this winter are most likely to be near or a little milder than the long term average (which does not rule out some frost). The second half of the winter may well be relatively milder than the first half when compared to the average for the individual months.

The early part of winter may be drier than average but this is likely to be offset by wetter weather later. (This would be different from the long term average in which December and January are wetter than February). Overall near normal or above normal precipitation is most likely for the  N and W of the Region with parts of the SE and E of Devon, E Somerset and Dorset closer to normal and in places a little below normal. Below average snowfall is more likely than above average, which means some snow accumulation over the moors but not much elsewhere.

Chance of increased number of storms in January and possibly February although the tracks may be to the north of the Region.

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 (2017 March April and May) :

Slightly above average temperatures are most likely for the season as a whole. Rainfall probably above normal overall  with near or below normal precipitation early in Spring offset by wetter than normal April and/or May.

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.

Limted data early look at Summer 2017  (June July August) 2016:

Conflicting temperature forecast perhaps suggesting near normal values. Rainfall, hint at drier June and/or July and wetter August which is not unusual.

(1981 to 2010 average 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 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. October 2016 issue.

Update 2 Nov 2016 see Forecast for November

(First Published 17 October 2016.)

CFS and UKMO model data from the end of October suggested that a drier than normal November with near normal or below normal temperatures is probable.

1. Potential influences.

Changes in sea temperature since mid September.

sstanom171016

Sea temperature around the UK remain above normal but the colder area in the North Atlantic has expanded a little more. The La Nina in the Pacific remains fairly week and is expected to weaken further during the course of the winter months as shown by the consensus probability forecast below.

nino

Whilst the La Nina is occurring it may be useful to look at the statistical relationship between the La Nina and precipitation in the UK area as shown in the graphic below. This suggest that the N and NW may be wetter than normal with other areas near normal or drier but given that the La Nina is fairly weak then the linkage may be unreliable.

DJFnina

Probability of drier/wetter/drier than normal during a La Nina event in the winter months. Published by IRI.

Numerical (model) output.

A summary of the output for UK and Eire from several international seasonal models can be seen in the UK and Eire summary at www.weatherservice.co.uk.  None of the available models suggest a colder than normal winter.

NMME output for November 2016 to February 2017 continues to show above normal temperatures although only slightly across the south in January, which is similar to last months forecast but with the lowest anomaly moved to January rather than December in the previous data. Precipitation signal has reduced across the SW compared to last months data but may just about end up above normal at least in northern and western parts of SW England for the winter season.

nmme

NMME  October 2016 data. Top row forecast monthly mean temperature anomaly. Bottom row indication for above (orange) and below (blue) monthly precipitation rate.

Indication for enhanced Atlantic westerly Jet flow has reduced compared to last month although still evident in some of the CFS2 output (later in the winter) but not at all clear in the NMME data. Both sets of anomaly suggest above normal heights across the S of UK.

z2001016

Top CFS2 mean and height anomaly at 200hPa. Bottom NMME height anomaly.

 

2. Forecast.

Remainder of Autumn  2016 (November):

High pressure and easterly winds have recently brought temperatures nearer to normal from above normal in September and rainfall has so far been below normal for the first half of Autumn at least to the east of the moors. Although further periods of easterly winds are possible with drier than normal weather types over the UK in the second half of October this may not be true for parts of the SW of UK. For November there is broad agreement that temperatures  will again be above normal and a return to wetter than normal weather is more likely than not. UPDATE 2 Nov 2017: CFS and UKMO model data from the end of October suggested that a drier than normal November with near normal or below normal temperatures is probable.

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  (2016 December, 2017  January and February) :

The winter is most likely to be milder than the long term average ( which does not rule out some frost), although parts of January and February may see temperatures only slightly above normal. This is a slightly less mild forecast than last month. (If this becomes a trend to colder type sin model data issued after the 17th then an updated may be added to this forecast.)

Near normal or above normal precipitation across the SW is most likely for the season. The N and W of the region in particular is more likely to have above normal rainfall and the SE and E parts of Devon, E Somerset and Dorset might be a little drier than normal.Below normal snowfall is more likely than above normal, which means just a little snow accumulation over the moors but not much elsewhere.

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 (2017 March April and May) :

Above average temperatures are most likely with near or below normal precipitation early in Spring made up to some extent by a wetter than normal May.

(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. September 2016 issue.

Published 17 September 2016.

Potential influences that might affect the forecast:

SEA TEMPERATURE.

anomnight-9-15-2016

NOAA/NESDIS night time sea temperature anomaly 15 September 2016

The area of below normal sea temperature in the north Atlantic has expanded somewhat during September possibly due to overturning/up-welling caused by fairly frequent areas of low pressure/strong winds in this area. This contrasts with the warm anomalies in the North Sea, Baltic and to the SW of the UK. The cold anomaly may impact on temperatures later in the winter if this expands and winds are as typical westerly but in the Autumn the residual warmer temperature around the UK may help keep temperatures above normal.

It was anticipated that, after the Pacific El Nino of 2015/16, a La Nina event would follow as is mostly the case. The La Nina however has so far been very week and barely cooler than cool Neutral Conditions. The forecasts produced by various models since late 2013 has been assembled by by IRI and is shown below:

ensofcst_dynam_sep16_l

The most recent multi model forecast for the Nino3.4 location shows that most models suggest only a weak La Nino through the winter then a rise in sea temperature.

figure4

The latest probability forecast (below) suggests that Neutral conditions are most likely to prevail.

figure1

A consequence of the weaker than expected La Nina is that the statistical relationship between rainfall in the UK area and La Nino is unlikely to be helpful.

MODEL OUTPUT.

A text summary of several seasonal model outputs can be seen in the UK and Eire summary at www.weatherservice.co.uk. The models show reasonable agreement with regards to temperature but much less consensus in the precipitation output (which is often the case).

CFS2 200hPa (15 Sept 2016) ten day ensemble monthly mean forecast and anomaly suggests an enhanced westerly jet strength across the Atlantic, initially across the north and mostly in central and the West of the Atlantic during November and February. In December some upper level ridging is suggested but in January a more generally cyclonic pattern is suggested over the UK area.

z200

The NMME temperature and rainfall anomaly forecast for the period October 2016 to February 2017 is shown below:

ondjf

The lowest temperature anomaly is show for December with above normal rainfall for SW England except in November and to a lesser extent in October and December

 

Forecast:

Remainder of Autumn  2016 (October and November):

Good agreement with respect to the temperature which is likely to be above normal through October and November. There is a chance of some very mild spells.

Rainfall probably near or below normal taking the two months together but with some longer dry spells quite likely especially in the SE and E of the Region. Uncertain as to which month has the best chance of the drier spells with recent forecasts suggesting November but earlier ones October.

 (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  (2016 December, 2017  January and February) :

A mild winter is most likely (does not rule out some frost), although December may see temperatures closer to normal. In January and February temperatures probably above normal, possibly very mild at times.

Near normal or above normal rainfall across the SW is most likely for the season as a whole. The N and W of the region is most likely to have above normal rainfall. There is a chance that SE and E parts of Devon and Dorset might be a little drier than normal for periods in December and possibly February too but make up for this in January. Below normal snowfall is more likely than above normal which means just a little snow accumulation over the moors but not much elsewhere.

(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 (2017 March April and May) :

The limited data available for this period suggests milder and wetter than normal.

(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.)

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

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/

Stratospheric images prepared by Freie Universität Berlin using European Centre for Medium Range Weather Forecasting data supplied by Deutscher Wetterdienst

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

CFS2  info