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

Published 20 August 2017.

1. Influences.

Changes in sea temperature.

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.

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.

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

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.

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

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.

NMME Sep to Nov 2017 temperature anomaly

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.

NMME precipitation anomaly for September to November 2017

NMME precipitation anomaly December 2017 to February 2018

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.

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.

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.

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.

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

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.

CFS2 mean monthly 200hPa heights and anomaly August to November

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.

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.

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.

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

Verification. Recent results June 2017.

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.

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.

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.

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.

 

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.

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

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

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

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.

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.

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.

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

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

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.

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

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

 

Experimental Long Range Forecast for SW England. March 2017.

Published 18 March 2017.

1. Potential influences.

Changes in sea temperature.

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.

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.

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.

 

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.

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.

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.

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

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.

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.

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

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:

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.

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