Review and Experimental Long Range Forecast for SW England. July 2018 issue.

Published 18 July 2018

GDPR statement: Please note that the author of this blog does not set cookies but the host “wordpress.com” sets multiple cookies which are outside of the authors control. You can view their cookie policy here. 

1. Influences.

Changes in sea temperature.

170718

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

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

170718sst

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

ENSOEC0718

ECMWF ENSO 3.4  SST forecast

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

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

elninonormal

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

170718nao

For background information see the Met Office NAO information.

Recent Climatology

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

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

scat0718

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

TandR0718

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

soil40718

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

river0718

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

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

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

glofas0718

Atmosphere predictions.

A: Upper Troposphere

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

z200SON0718

200hpa mean height and anomaly Sep to Nov 2018

z200DJF0718

200hPa mean height and anomaly December 2018 to February 2019

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

B: Lower Troposphere:

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

ASONNMME0718

NMME top temperature bottom precipitation (orange above normal)

ASONE30718

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

ASONEC0718

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

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

December 2018 to February 2019.

 

DJFNNME0718

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

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

C: Recent results/comments:

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

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

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

2. Forecast.

Remainder of Summer 2018  (August). 

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

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

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

August climate: 1981 to 2010 average daily mean temperature 16 or 17°C in many areas, a little cooler over the N coastal areas of Devon and Cornwall  to 16 or 17°C  and a few degrees cooler over the moor. Locally over 17C in parts of Somerset.  Average rain in August typically 60 to 80mm, but 40 to 60mm in places especially East of the moors and in Somerset. Locally over 100mm across the moors.

Autumn 2018  (September October November) early indications. 

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

Rainfall near normal for the season but with a drier than average September and parts of October followed by a much wetter period into November.

Autumn climate: 1981 to 2010 average mean temperature 11 or 12°C but nearer 10°C in rural areas. Maximum temperatures average 14 to 16°C. November normally colder than October which is colder than September. Average 1981 to 2010 rain 300 to 400mm, 600 to 800mm over the moors but east of the moors and in lowland Somerset more like 200 to 300mm. September often drier than October or November.

Winter 2018/9  (December January and February) limited data from 4 models. 

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

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

Winter Climate: 1981-2010 average temperature values for lowland areas 7°C in the West and 5°C in the East. Rainfall; Dec and Jan typically wetter than February. 1981-2010 Autumn average 300-400 mm lowlands but 200-300 mm areas to E of Dartmoor. Snow climatology less than 5 days lying snow over lowland areas 5 to 10 hills, say hills around 200 metre elevation – one in three years have no lying snow.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary can be seen at  www.weatherservice.co.uk

The attempt at a Regional Forecast for SW England aims to test whether such a forecast of temperature and rainfall variation from average can be made using numerical model data available on the internet. The forecast should not be used for any other purpose. A brief verification summary for the UK and Eire is routinely published at http://www.weather-info.co.uk/wxsvc/Verification.html or Click here for the Teignmouth and Dawlish summary

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

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

CFS2  info

GLOFAS Acknowledgement: Data were provided by the Global Flood Awareness System – GloFAS (http://www.globalfloods.eu/) of the European Commission Joint Research Centre and the European Centre for Medium-Range Weather Forecasts.
Reference: Alfieri, L., Burek, P., Dutra, E., Krzeminski, B., Muraro, D., Thielen, J., and Pappenberger, F.: GloFAS – global ensemble streamflow forecasting and flood early warning, Hydrol. Earth Syst. Sci., 17, 1161-1175, doi:10.5194/hess-17-1161-2013, 2013.

‘Copernicus Products’  as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus  http://climate.copernicus.eu

ECMWF seasonal monthly data from weather.us

Stratospheric Diagnostics from Free University Berlin

Climate data from The Met Office UK and NCEP USA.

 

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Review and Experimental Long Range Forecast for SW England. June 2018 issue.

Published 19 June 2018

GDPR statement: Please note that the author of this blog does not set cookies but the host “wordpress.com” sets multiple cookies which are outside of the authors control. You can view their cookie policy here. 

1. Influences.

Changes in sea temperature.

anomnight.6.14.2018

Sea temperature around the UK has continued to recover due to the frequent winds from the east and the area of colder than normal Atlantic to the west of the UK has reduced in area. Despite this winds from the west may contain increased cloud due to cooling by the cooler than average sea temperatures further WNW.

The Tropical Pacific (ENSO 3.4 area) is now in a neutral phase and moving towards El Nino. This is a slightly faster transition than CFS2 was suggesting but in line with the ECMWF forecast. The June EC forecast, shown below, suggests slightly stronger warming than earlier forecast by Autumn.

ecenso0618

Tropical Atlantic sea temperature is also showing signs of returning to nearer normal values and is forecast to be increase to near or slightly above normal during August.

sea1062018

Left: CFS2 ENSO 3.4 area forecast. Right: UKMO tropical Atlantic sea temperature forecast.

The statistical predictor for UK rainfall based on the Pacific Sea Temperature anomalies remains unlikely to be of use until the Autumn.

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) has been positive for some time and the predicted to move to a negative state in the second half of May was delayed and soon reversed. The recent forecast shown below again trends to a neutral or negative (more mobile state) but does not look a string signal.

NAO062018

For background information see the Met Office NAO information.

Recent Climatology.

June across the SW of England has so far been very dry and warm. Some areas having 1% or less of the typical monthly rainfall with temperature means almost 2C above average.

tandr0618

Although March was cold, April and May saw warmer temperatures bringing the spring average to near normal and it looks like the April May June period will be well above average. April was the wetter month recently but May and June (so far) were below normal.

In the short term rainfall is likely to remain low over SW England leading to reduced soil moisture content as shown by the GFS forecast until 26th June. In Summer it is normal for soil moisture to reduce due to greater evaporation.

soil4

Rover flows in May reflect the recent drier period and whist still normal were showing signs of reduction. The full Hydrological Summary for  May is available from this link  – May 2018 summary PDF 

riverflow0618

The reservoir levels in the SW of England (10th June) continue to show above normal storage for the time of year.

The experimental product from the Global Flood Awareness System suggests enhanced flood risk, compared to the average risk, for the SW of England for the four months starting 1st June 2018 based on ECMWF forecast.

This looks to be biased towards the river states in May (see above) following the wet April. Catchment forecasts in the south of England show a rapid fall in risk from early in the forecast and given that EC forecast suggest drier summer month the area colour coding for increased flood risk looks misleading for the SW of England.   

glofas062018

Atmosphere predictions.

A: Upper Troposphere

CFS2 data (as supplied to NNME data set June 2018) for 200hPa continues to suggest above normal heights across the UK and possibly reduced jet strength through Summer.

cfs2z2000618

For the Autumn indications of stronger than normal mid Atlantic jet strength suggests a wetter and windier October is possible.

cfs2z200son0618

B: Lower Troposphere:

Comparing temperature and rain forecast anomalies from NMME, CFS2 and ECMWF systems. Note the rain rate colour scheme is different / reversed in ECMWF output compared to NMME and CFS2.

July August and September 2018.

nmmejas0618

NMME July to Sept. Top: Temperature anomaly. Lower: Rain Rate anomaly

e3jas0618

CFS2 E3 10 day mean of runs. Top Temperature. Lower row Rain rate (Orange above normal).

ECJAS062018

ECMWF Top  row Temperature anomaly Lower row Rain anomaly (Orange below normal)

The E3 version of CFS2 looks to be colder but anomalies are small. The CFS2 data set up to 16th June was colder than the data to 7th June but for the three month season July to September values end up above normal for SW England. Rainfall, as is often the case, is more variable between models. CFS2 has over several runs had a tendency to produce more rain over southern England during August.

September October November 2018.

e31son

CFS2 E3 version data 7 June

e3son0618

CFS2 E3 version data 16 June (Lower row Blue drier)

Two sets of CFS2 E3 mean of 19 days output are shown above for comparison with the newer slightly colder than the earlier data but still suggesting a milder than average season.

nmmeson0618

NMME Sept Oct Nov 2018 (Lower row Blue drier)

ECSON062018

ECMWF September October November (Lower row Blue wetter)

No indication for below normal temperatures and suggestion of a wetter period to come but differences as to which month starts wetter October or November looks favourite.

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

C: Recent results/comments:

February data was again fairly poor as can be seen in the review of forecast for Spring 2018 .

“Original Summary – 170218 – Models were slow to pick up on the start of a colder than normal sequence in February but now suggest March will be near or a little colder than normal, followed by a trend towards normal or above normal through April and May. Overall near normal temperature for the season.”

Good. The trend to less cold was correct although season ended up slightly milder except in N Ireland (near normal).

“Precipitation may well be below normal to start the period especially in the North but with a trend to above normal, especially for May. Little agreement between systems for location of above normal rainfall. Overall precipitation near normal for the season.”

Fair. Trend was OK but March was much wetter and May was drier in many places although heavy rain/thunderstorms brought some locally above normal rain in central areas of England and E Wales.

A brief review of other seasonal forecasts can be seen at the verification index.

2. Forecast.

Remainder of Summer 2018  (July and August). 

Most likely a warmer than average July and possibly nearer normal values in August although night time temperatures may be above average throughout due to cloudier skies, especially in western parts of the region.

Drier than normal conditions may continue for parts of July but some uncertainty for August with some indication that August could be wetter probably in the north and east of the region due to thunder showers . It is uncertain whether this could be wetter due to a greater number of wet days or higher rainfall rates. The latter has been a feature of some rainfall patterns and can occur with less “wet” days in a month.

Pressure is likely to be above normal across the UK, especially the north.

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 2018  (September October November) early indications. 

Milder than normal for the season as a whole but possibly starting off in September near normal with stronger anomalies later in the season.

Rainfall near or above normal but starting drier in September and then uncertainty whether October or November will be the wetter of the months,

Autumn climate: 1981 to 2010 average mean temperature 11 or 12°C but nearer 10°C in rural areas. Maximum temperatures average 14 to 16°C. November normally colder than October which is colder than September. Average 1981 to 2010 rain 300 to 400mm, 600 to 800mm over the moors but east of the moors and in lowland Somerset more like 200 to 300mm. September often drier than October or November.

Winter 2018/9  (December January and February) limited data from 4 models. 

A mild start to winter but trending below normal temperatures in February, resulting in a slightly milder winter than average. Wetter than average winter despite near or below normal precipitation in February. Below average snowfall, though slightly increased risk during February compared to normal.

Winter Climate: 1981-2010 average temperature values for lowland areas 7°C in the West and 5°C in the East. Rainfall; Dec and Jan typically wetter than February. 1981-2010 Autumn average 300-400 mm lowlands but 200-300 mm areas to E of Dartmoor. Snow climatology less than 5 days lying snow over lowland areas 5 to 10 hills, say hills around 200 metre elevation – one in three years have no lying snow.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary can be seen at  www.weatherservice.co.uk

The attempt at a Regional Forecast for SW England aims to test whether such a forecast of temperature and rainfall variation from average can be made using numerical model data available on the internet. The forecast should not be used for any other purpose. A brief verification summary for the UK and Eire is routinely published at http://www.weather-info.co.uk/wxsvc/Verification.html or Click here for the Teignmouth and Dawlish summary

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

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

CFS2  info

GLOFAS Acknowledgement: Data were provided by the Global Flood Awareness System – GloFAS (http://www.globalfloods.eu/) of the European Commission Joint Research Centre and the European Centre for Medium-Range Weather Forecasts.
Reference: Alfieri, L., Burek, P., Dutra, E., Krzeminski, B., Muraro, D., Thielen, J., and Pappenberger, F.: GloFAS – global ensemble streamflow forecasting and flood early warning, Hydrol. Earth Syst. Sci., 17, 1161-1175, doi:10.5194/hess-17-1161-2013, 2013.

‘Copernicus Products’  as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus  http://climate.copernicus.eu

ECMWF seasonal monthly data from weather.us

Stratospheric Diagnostics from Free University Berlin

Climate data from The Met Office UK and NCEP USA.

 

Review and Experimental Long Range Forecast for SW England. May 2018 issue.

Published 18 May 2018

GDPR statement: Please note that the author of this blog does not set cookies but the host “wordpress.com” sets multiple cookies which are outside of the authors control. You can view their cookie policy here. 

1. Influences.

Changes in sea temperature.

anomnight.5.17.2018

Sea temperatures in the North and East Atlantic, to the west of the UK, remain generally below normal although further to the SW there looks to be a large area with above normal values. The colder than normal sea temperatures may impact UK temperatures when winds are from a Westerly point. Conversely due to a warmer than normal central Europe and more frequent winds from an Easterly point North Sea temperatures have recovered remarkably and show a strong positive anomaly. Elsewhere the anomalies are not very different to last month.

Sea temperatures in the tropical Atlantic are slightly below average but expected to recover over the next few months as shown by the UK Met Office plot below (left).

ENSO0518

Left: UKMO Tropical North Atlantic forecast. Right: Pacific ENSO 3.4 area forecast.

The La Nina in the Pacific continues to weaken  with models suggesting and move to neutral conditions then a warming to an El Nino state in the Autumn of 2018.

EC010518ENSO

Differences between ECMWF and CFS2 illustrate the uncertainty in a move to El Nino. Any statistical predictor for UK rainfall based on the Pacific Sea Temperature anomalies is unlikely to be of use.

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) has been positive for some time but is predicted to move to a more variable perhaps negative state in the second half of May.

NAO0518

For background information see the Met Office NAO information.

Changes in the upper atmosphere.

The stratosphere remain in summer mode as shown by the 50hPa ECMWF analysis for 17th May 1200UTC,shown below:ecmwf50a12

Recent Climatology.

climat180518

Following a colder than normal March temperature recovered to above normal in April. Despite the N/NW of the UK remaining drier than normal elsewhere rainfall totals were above normal in much the same areas as in March. Away from the NW of the UK, the six month rainfall period changed from near normal/drier to the end of March to above normal. May 2018 though has been drier than normal so far except perhaps in the NW of the UK.

River flows for April reflect the wetter month (see below) and reservoir levels in the SW of England (13th May) show above normal storage for the time of year. The full Hydrological Summary for April is available from this link  – April 2018 summary PDF 

180518riverflow

Looking ahead, the experimental product from the Global Flood Awareness System suggests enhanced flood risk, compared to the average risk, for the SW of England for the four months starting 1st May 2048. This is based on the early May monthly ECMWF seasonal forecast and seems heavily biased to rainfall in March and April because EC output looks for drier than normal conditions for SW England.

180518glofas

Atmosphere predictions.

A: Upper Troposphere

CFS2 data (as supplied to NNME data set May 2018) for 200hPa continues to suggest above normal heights across the UK and possibly reduced jet strength through Summer.

z200JJA0518

CFS2 200hPa heights (top) and anomalies (below) June to August. May 2018 data.

z200SON0518

CFS2 200 hPa mean heights and anomalies September to November

During the Autumn despite above normal heights there are signs of increased Jet flow along 50 deg N in October and perhaps more troughs / blocking near the UK in November.

B: Lower Troposphere:

Summer:  June July August 2018. Caution rain rate colour scheme different / reversed in ECMWF output compared to NMME and CFS2.

Anomalies for temperature are less than 1 degree C in all output. For SW England there is some agreement for above normal values. Rain rate also indicate below normal rainfall for SW England although the agreement elsewhere in the UK is not so clear

100518NMME

NMME muli model ensemble output 7 May data. Top Temperature Bottom rain rate anomaly. 

100518NCEPE3

CFS2 10 day mean output 13 May data. Top Temperature Bottom rain rate anomaly (red wetter)

ECJJA052018

ECMWF Top Temperature Bottom Rain rate anomaly (note rain has blue for wetter)

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

C: Recent results/comments:

The following images show a comparison between observed and forecast for one month ahead and illustrates the lack of reliability in any one system.

1: RAIN RATE ANOMALY

Forecast rain rate anomaly in January for February 2018 were mostly poor. UKMO Contingency issued after Stratospheric warming had occured captured the drier theme

February2018PPNverif

Data January 2018 for February 2018

Better Forecast in February for March rainfall but not UKMO Contingency

March2018PPNverif

Data February for March 2018 Precipitation

Data in March for April rather variable but NCEP had correct idea.

April2018PPNverif

Data March for April 2018 Precipitation

2: TEMPERATURE ANOMALY:

March2018verif

Temperature anomaly February for March

April2018verif

Temperature anomaly for March for April 2018

A brief review of each seasonal forecast can be seen at the verification index.

2. Forecast.

 

Summer 2018  (June July August). 

Most likely a warmer than average summer although June may be closer to normal but with warmer than average months to follow. Cooler values most likely in the west of the region with westerly winds due to cooler than normal sea temperature early in the season.

Drier than normal but some uncertainty for August with some indications that August could be wetter – uncertain whether this is wetter due to more wet days or higher overall rainfall (which can occur with less wet days in a month). Summer rain often uncertain due to increased convective elements which increase the variability of rain totals across regions.

Pressure is likely to be above normal across the UK which implies a better than average summer.

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 2018  (September October November) early indications. 

Milder than normal for the season as a whole but with larger anomalies later in the season. Rainfall starting near or below normal in September and possibly October but November wetter than average which may make the season slightly wetter than average.

Autumn climate: 1981 to 2010 average mean temperature 11 or 12°C but nearer 10°C in rural areas. Maximum temperatures average 14 to 16°C. November normally colder than October which is colder than September. Average 1981 to 2010 rain 300 to 400mm, 600 to 800mm over the moors but east of the moors and in lowland Somerset more like 200 to 300mm . September often drier than October or November.

Winter 2018/9  (December January and February) very limted data. 

Slightly milder than an average winter possibly colder than average in January.Milder start to winter but trending nearer average values during January and/or February.  Precipitation very uncertain slightly more solutions suggest above normal. Near normal snowfall (hence mostly 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 can be seen at  www.weatherservice.co.uk

The attempt at a Regional Forecast for SW England aims to test whether such a forecast of temperature and rainfall variation from average can be made using numerical model data available on the internet. The forecast should not be used for any other purpose. A brief verification summary for the UK and Eire is routinely published at http://www.weather-info.co.uk/wxsvc/Verification.html or Click here for the Teignmouth and Dawlish summary

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

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

CFS2  info

GLOFAS Acknowledgement: Data were provided by the Global Flood Awareness System – GloFAS (http://www.globalfloods.eu/) of the European Commission Joint Research Centre and the European Centre for Medium-Range Weather Forecasts.
Reference: Alfieri, L., Burek, P., Dutra, E., Krzeminski, B., Muraro, D., Thielen, J., and Pappenberger, F.: GloFAS – global ensemble streamflow forecasting and flood early warning, Hydrol. Earth Syst. Sci., 17, 1161-1175, doi:10.5194/hess-17-1161-2013, 2013.

‘Copernicus Products’  as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus  http://climate.copernicus.eu

ECMWF seasonal monthly data from weather.us

Stratospheric Diagnostics from Free University Berlin

Climate data from The Met Office UK and NCEP USA.

Review and Experimental Long Range Forecast for SW England. April 2018 issue.

Published 19 April 2018

GDPR statement: Please note that the author of this blog does not set cookies but the host “wordpress.com” sets multiple cookies which are outside of the authors control. You can view their cookie policy here. 

1. Influences.

Changes in sea temperature.

anomnight.4.16.2018

Due to the cold March and start of April sea temperatures around the UK are generally below normal, in particular North Sea temperatures show a strong negative anomaly.  This continues to have potential impact on temperatures across the UK during the remainder of April and into May and may also result in increased sea fog or haar. Elsewhere the anomalies are not very different to last month with North Atlantic anomalies marginally lower. Sea temperatures in the tropical Atlantic are slightly below average but expected to recover over the next few months as shown by the UK Met Office plot below (left).

NINO0418

Left: UKMO Tropical North Atlantic Sea Temperature forecast.                                                      Right: CFS2 Tropical Pacific Nino 3.4 area Sea Temperature Forecast

The La Nina in the Pacific although well established  (as shown by the sea temperature anomaly chart at the top of the page) but is showing signs of weakening. The consensus from the models (see graphic below) is for a move to neutral and then weak El Nino conditions later in the year.

figure1

ECMWF and multi model comparison for ENSO conditions (April output)

A consequence is that the IRI relationship between ENSO and UK rainfall is likely to be unreliable and is not reproduced in this document.

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) has been rather variable over recent weeks but is forecast to return to a positive phase after a short negative dip during the second half of April.

nao170418

or more information see Met Office NAO information.

Changes in the upper atmosphere.

The stratospheric polar vortex is now history with a generally slack pressure pattern as shown by the 50hPa ECMWF analysis below.

ecmwf50a12

Recent Climatology.

march2018

The Met Office stated that for March 2018 “The provisional UK mean temperature was 3.8 °C, which is 1.6 °C below the 1981-2010 long-term average, but it was significantly less cold than March 2013.”

March was a very unsettled month with Low Pressure dominating the weather patterns across the United Kingdom. In addition, there were two periods of snow across SW England which is very unusual. Rainfall measurements during snow can be a problem but looking at the water equivalent and adding this to the other rainfall brought rainfall totals in the Dawlish and Teignmouth area, for example, to between 170mm and 250mm for the month. This was roughly three times more rainfall than an average March. There were at least eighteen wet days which was well above normal.

Rainfall was well above average across the UK except in the NW where totals were below normal. Looking at the October 2017 to March 2018 rainfall totals these have not been far from average and if anything a little below normal across northern areas.

River flows for March reflect the wetter month (see below) and reservoir levels are  above normal storage for the time of year. The full Hydrological Summary for February is available from this link  – March 2018 summary PDF 

riverflowsmarch2018

Looking ahead, the experimental product from the Global Flood Awareness System suggests enhanced flood risk, compared to the average risk, for the SW of England for the next 4 months. This is based on the early April monthly ECMWF seasonal forecast and represents a marked change from last month experimental forecast.

glofas0418

The left hand graph and probability tables for the River Severn illustrate the change in forecast which now has high probs of a flood risk compared to last months forecast.

Atmosphere predictions.

A: Upper Troposphere

CFS2 data (as supplied to NNME data set April 2018)  for 200hPa suggests above normal heights across the UK and possibly reduced jet strength through Summer but continues to hints at increased troughing in summer or at least relatively reduced anomalies.

z200JJA0418

200hPa mean height June July August with anomalies below.

In the Autumn, October looks to have a risk of enhanced jet flow with reduced flow over UK in September and November.

z200SON0418

200hPa mean height September October November with anomalies below.

B: Lower Troposphere:

Model data is not in good agreement but in general shows a warming trend relative to normal through the summer but hints at cooler start to summer across the SW of the Uk.

Not much agreement with regards to rainfall with ECMWF in particular at odds with other models with regards drier August a;though some support from NMME.

NMMEJJA0418

NMME temperature anomaly forecast (top) and rain rate (below) May June July and August

CFS2E3JJA0418

CFS2 (mean of 10 days output) Temperature anomaly forecast (top) and rain rate (below) for June July and August

120418SEASONMtoSECMWF

ECMWF Temperature anomaly forecast (top) and rain rate (below) for May  June July and August

Top row of each set, temperature anomaly (+ oranges or in EC green). Lower row indication for above or below normal rainfall (reds are above normal in NMME and CFS2 but below normal in EC).  (Note NCEP is a part of the NMME multi model ensemble).

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

C: Recent results/comments:

Looking at the verification summary for January to March models generally failed to get the colder types but got some idea of wetter than average but not the month to month variation

2. Forecast.

Remainder of Spring 2018 (May):

Temperature during May probably near normal for the region as a whole but perhaps slightly cooler than average in the west and a little above inland in the east.

Conflicting indications for rainfall but main indication is for near or above normal rainfall the above normal values possibly in the S and W of the region.

 

May climate: 1981-2010 average mean temperature roughly 11 or 12°C but a little warmer over parts of Somerset and nearer 9°C over the Moors. Average 1981 to 2010 rain 80mm to 100mm but 60mm to 80mm in parts of Somerset, the Exe Valley and East Dorset but over 100mm across the Moors.

Summer 2018  (June July August). 

 

Temperature: near normal for the season possibly with cooler than normal start and warmer than normal August.
Rain: Indication for normal or below normal rainfall for the season but monthly data uncertain about the wetter month(s) though possibly August the wettest (compared to average) with the higher rain rates. Note CFS and ECMWF pretty well opposite signals. CFS preferred but most models were poor with 2017 summer rain rate anomalies. 

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 2018  (September October November) early indications. 

Temperature near or slightly above average. Rainfall near normal but may start the season drier than average making up for the rain totals later in the season.

Autumn climate: 1981 to 2010 average mean temperature 11 or 12°C but nearer 10°C in rural areas. Maximum temperatures average 14 to 16°C. November normally colder than October which is colder than September. Average 1981 to 2010 rain 300 to 400mm, 600 to 800mm over the moors but east of the moors and in lowland Somerset more like 200 to 300mm . September often drier than October or November.

Winter 2018/9  (December January and February) minimal data. 

Milder start to winter but trending nearer average values during January and/or February. Wetter than average early in the winter but perhaps a drier February. Near normal snowfall so little if any snow on lower ground but some snow 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 can be seen at  www.weatherservice.co.uk

The attempt at a Regional Forecast for SW England aims to test whether such a forecast of temperature and rainfall variation from average can be made using numerical model data available on the internet. The forecast should not be used for any other purpose. A brief verification summary for the UK and Eire is routinely published at http://www.weather-info.co.uk/wxsvc/Verification.html or Click here for the Teignmouth and Dawlish summary

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

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

CFS2  info

GLOFAS Acknowledgement: Data were provided by the Global Flood Awareness System – GloFAS (http://www.globalfloods.eu/) of the European Commission Joint Research Centre and the European Centre for Medium-Range Weather Forecasts.
Reference: Alfieri, L., Burek, P., Dutra, E., Krzeminski, B., Muraro, D., Thielen, J., and Pappenberger, F.: GloFAS – global ensemble streamflow forecasting and flood early warning, Hydrol. Earth Syst. Sci., 17, 1161-1175, doi:10.5194/hess-17-1161-2013, 2013.

‘Copernicus Products’  as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus  http://climate.copernicus.eu

ECMWF seasonal monthly data from weather.us

Stratospheric Diagnostics from Free University Berlin

Climate data from The Met Office UK and NCEP USA.

 

Experimental Long Range Forecast for SW England. March 2018 issue.

Published 20 March 2018. (correction July rainfall 02April)

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1. Influences.

Changes in sea temperature.

anomnight.3.15.2018

Sea Temperatures have cooled relative to average around the UK and western Europe due to the cold easterly types early and middle March know as the “Beast from the East” and “mini Breast from the East”, resulting partially from the sudden stratospheric warming during February. This is likely to have impact on temperatures across the UK during the remainder of  March and at least for the start of April. Elsewhere the anomalies are not very different to last month with North Atlantic anomalies still above average. Sea temperatures in the tropical Atlantic area have continued to cool and are forecast remain slightly below average for the next few months as shown by the UK Met Office plot below.

tna_anom_20180301

The La Nina in the Pacific is well established (as shown by the sea temperature anomaly chart at the top of the page) with a large area of below normal sea temperatures in the eastern Pacific near the equator. The CFS2 forecast for the La Nina suggests it may continue as a weak feature through summer and autumn, as shown by the graphic below (top right panel). This is not supported by either UKMO or ECMWF forecast which trends to neutral or El Nino conditions. A consensus appears to be more towards the Neutral/El Nino than staying with a weak La Nina.

SST1

A consequence is that the IRI relationship between ENSO and UK rainfall is likely to be unreliable and is not reproduced in this document.

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) went into a negative phase, as suggested by some models, late in February but may well return to a positive phase over the next few weeks.

SST2

For more information see Met Office NAO information.

Changes in the upper atmosphere.

A sudden stratospheric warming (SSW) did develop from about the 12th February leading to a reversal in the stratospheric winds over the UK area and a weakening of the jet stream across the Atlantic. Tokyo issued a STRATALERT EXISTS message and a final END message on the 16th March. ECMWF 30hPa chart for 12Z 11th February and 12Z on the 18th March 2018 shows the effect of the warming on the stratospheric polar vortex which is well on the way to “summer” mode.

SSW

Analysis and Numerical (model) output.

A: Recent Climatology.

recent climat

February was colder and drier than normal but for the winter as a whole temperatures in the south of UK were near average and for the SW rainfall was not far from normal though slightly wetter in the west and drier in parts of the SE of the region. March so far has continued with the cold theme with temperature anomalies over 1 degree below the average. Rainfall (snowmelt) looks to be well above normal in the west but less so in the east.

river River flows for February reflect the drier month but have no doubt made up for it since as can be seen in the recent reservoir levels which indicate above normal storage for the time of year. The  full Hydrological Summary for February is available from this link  –  February 2018 summary PDF 

Looking ahead, the experimental product from the Global Flood Awareness System suggests no enhanced flood risk, compared to the average risk, for the SW of England for the next 4 months. This is based on the early March monthly ECMWF seasonal forecast.

glofas

B: Upper Troposphere

CFS2 forecast for 200hPa suggests above normal heights across the UK and possibly reduced jet strength through Spring  but again hints at increased troughing in summer.

200

C: Lower Troposphere:

Comparing monthly data from the NMME (8th March), NCEP ensemble 10 day mean (15th March) and ECMWF (15th March) seasonal forecasts for summer 2018.

summary

Top row of each set, temperature anomaly (+ oranges). Lower row indication for above or below normal rainfall (reds are above normal in NMME and CFS2 but below normal in EC). The stronger dry signals in EC and NMME dont quite match but are clearly different to the wetter indication in the NCEP E3. There is good agreement for a colder April between NCEP and EC but not in the NMME output which tends to be a bit warm. (Note NCEP is a part of the NMME multi model ensemble).

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

D: Recent results/comments:

Recent seasonal models that provide month by month data were slow to pick up on the cold spell in February more than a month ahead and certainly not before the start of the winter season.  Verification details can be viewed here

summ2017 The plots above show a score out of three for the following three month forecast. ( Monthly score 0 no signal 1 poor 2 fair  and 3 good leading to a potential max of 36 for year)  This is done for each model/system for the season following the issue month. Temperature continues to be slightly better forecast than rainfall.

2. Forecast.

Remainder of Spring 2018 (April and May):

Temperatures may well start below normal in April but should recover to near normal and then above normal for May. The risk of air frosts continues into April, although probably not very frequent.

Rainfall probably below normal early April but then returning to normal with wetter spells for May especially in the west. Parts of the south and east of the region may well end up below normal for the the two months.  Snow is only likely on the tops of the moors for a time in April.

Spring climate: 1981-2010 average mean temperature 9 or 10°C but a few degrees cooler over the moors. Roughly Mar 7 or 8°C Apr 8 or 9°C  May 11 or 12°C. Average 1981 to 2010 rain 200 to 300mm lowest values in E Devon and over parts of Somerset. April is marginally wetter in western areas than May.

Summer 2018  (June July August). 

The temperature is most likely to be near or only very slightly above normal for the season. July may see larger anomalies than August.

Rainfall for the season is quite uncertain probably near or a little above the long term average but with a chance that July might be a little drier. Summer rainfall is often difficult due to showery nature leading to large variation in totals over the region. There is little agreement between the seasonal models with regards to which months might be wetter or drier.

Summer climate: 1981 to 2010 average daily mean temperature 14 or 15°C in many areas to 16 or 17°C in main urban areas also locally east of the moors and more widely in Somerset. Maximum temperatures average 19 to over 21°C in similar areas. July often warmer than August. Average 1981 to 2010 rain 300mm over the moors, typically 200 to 250mm in many coastal and eastern areas. June often drier than July and July drier than August.

Autumn 2018  (September October November) early indications. 

Temperature likely to be above normal and rainfall mostly above normal for season possibly wettest in October.

Autumn climate: 1981 to 2010 average mean temperature 11 or 12°C but nearer 10°C in rural areas. Maximum temperatures average 14 to 16°C. November normally colder than October which is colder than September. Average 1981 to 2010 rain 300 to 400mm, 600 to 800mm over the moors but east of the moors and in lowland Somerset more like 200 to 300mm . September often drier than October or November.

Winter 2018/9  (December January and February) minimal data. 

Temperature normal or above normal with variable precipitation month to month but probably ending up near normal for the season.

Winter Climate: 1981-2010 average temperature values for lowland areas 7°C in the West and 5°C in the East. Rainfall; Dec and Jan typically wetter than February. 1981-2010 Autumn average 300-400 mm lowlands but 200-300 mm areas to E of Dartmoor. Snow climatology less than 5 days lying snow over lowland areas 5 to 10 hills, say hills around 200 metre elevation – one in three years have no lying snow.

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary can be seen at  www.weatherservice.co.uk

The attempt at a Regional Forecast for SW England aims to test whether such a forecast of temperature and rainfall variation from average can be made using numerical model data available on the internet. The forecast should not be used for any other purpose. A brief verification summary for the UK and Eire is routinely published at http://www.weather-info.co.uk/wxsvc/Verification.html or Click here for the Teignmouth and Dawlish summary

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

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

CFS2  info

GLOFAS Acknowledgement: Data were provided by the Global Flood Awareness System – GloFAS (http://www.globalfloods.eu/) of the European Commission Joint Research Centre and the European Centre for Medium-Range Weather Forecasts.
Reference: Alfieri, L., Burek, P., Dutra, E., Krzeminski, B., Muraro, D., Thielen, J., and Pappenberger, F.: GloFAS – global ensemble streamflow forecasting and flood early warning, Hydrol. Earth Syst. Sci., 17, 1161-1175, doi:10.5194/hess-17-1161-2013, 2013.

‘Copernicus Products’  as listed in the C3S or CAMS Service Product Specification or any other items available through an ECMWF Copernicus  http://climate.copernicus.eu

ECMWF seasonal monthly data from weather.us

Stratospheric Diagnostics from Free University Berlin

 

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

Published 17 October 2017.

1. Influences.

Changes in sea temperature.

anomnight.10.12.2017

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

 

nino102017

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

ninoNAO

CFS Nino 3.4 forecast left. Observed NAO index right.

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

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

La Nina

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

Analysis and Numerical (model) output.

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

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

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

B: Upper Troposphere:

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

z200

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

C: Lower Troposphere:

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

NMME102017

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

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

E3DJF

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

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

2. Forecast.

Remainder of Autumn  2017  (November) :

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

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

Winter (2017 December, 2018  January and February) :

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

Rainfall is uncertain month to month but the main theme of a wetter than normal winter seems to be consistent although December may be less wet. The snow risk is reduced compared to average with little if any snow for lower ground but some snow for the moors.

Winter Climate: 1981-2010 average temperature values for lowland areas 7°C in the West and 5°C in the East. Rainfall; Dec and Jan typically wetter than February. 1981-2010 Autumn average 300-400 mm lowlands but 200-300 mm areas to E of Dartmoor. Snow climatology less than 5 days lying snow over lowland areas 5 to 10 hills, say hills around 200 metre elevation – one in three years have no lying snow.

Spring (2018 March April and May)  limted data:

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

Spring climate: 1981-2010 average mean temperature 9 or 10°C but a few degrees cooler over the moors. Roughly Mar 7 or 8°C Apr 8 or 9°C  May 11 or 12°C. Average 1981 to 2010 rain 200 to 300mm lowest values in E Devon and over parts of Somerset.

3. Caution.

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

The attempt at a Regional Forecast for SW England aims to test whether such a forecast of temperature and rainfall variation from average can be made using numerical model data available on the internet. The forecast should not be used for any other purpose. A brief verification summary for the UK and Eire is routinely published at http://www.weather-info.co.uk/wxsvc/Verification.html or Click here for the Teignmouth and Dawlish summary

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

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

CFS2  info

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

Published 19 September 2017.

1. Influences.

Changes in sea temperature.

anomnight.9.18.2017

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

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

SSTNINO

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

AO

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

Analysis and Numerical (model) output.

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

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

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

B: Upper Troposphere:

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

z2001

CFS2 200hPa height and anomaly Oct Nov Dec 2017

z200DJF

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

C: Lower Troposphere:

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

NMME1

NMME Temperature anomaly and rainfall index October and November 2017

NMMEDJF

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

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

2. Forecast.

Remainder of Autumn  2017  (October and November) :

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

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

Autumn climate: 1981 to 2010 average mean temperature 11 or 12°C but nearer 10°C in rural areas. Maximum temperatures average 14 to 16°C. November normally colder than October which is colder than September. Average 1981 to 2010 rain 300 to 400mm, 600 to 800mm over the moors but east of the moors and in lowland Somerset more like 200 to 300mm . September often drier than October or November.

Winter (2017 December, 2018  January and February) :

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

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

Winter Climate: 1981-2010 average temperature values for lowland areas 7°C in the West and 5°C in the East. Rainfall; Dec and Jan typically wetter than February. 1981-2010 Autumn average 300-400 mm lowlands but 200-300 mm areas to E of Dartmoor. Snow climatology less than 5 days lying snow over lowland areas 5 to 10 hills, say hills around 200 metre elevation – one in three years have no lying snow.

Spring (2018 March April and May)  limted data:

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

Spring climate: 1981-2010 average mean temperature 9 or 10°C but a few degrees cooler over the moors. Roughly Mar 7 or 8°C Apr 8 or 9°C  May 11 or 12°C. Average 1981 to 2010 rain 200 to 300mm lowest values in E Devon and over parts of Somerset.

3. Caution.

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

The attempt at a Regional Forecast for SW England aims to test whether such a forecast of temperature and rainfall variation from average can be made using numerical model data available on the internet. The forecast should not be used for any other purpose. A brief verification summary for the UK and Eire is routinely published at http://www.weather-info.co.uk/wxsvc/Verification.html or Click here for the Teignmouth and Dawlish summary

4. References.

SST anomaly NOAA Remote Sens. 2014, 6(11), 11579-11606; doi:10.3390/rs61111579

IRI statistics: Mason, S.J. and L. Goddard, 2001: Probabilistic precipitation anomalies associated with ENSO. Bull. Amer. Meteor. Soc., 82, 619-638.

UK climate details see: http://www.metoffice.gov.uk/public/weather/climate/

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

CFS2  info