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

Published 18 May 2018

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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.

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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)

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.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. Update to January 2018 issue.

Published 4 February 2018.

Update.

Expected changes in the stratosphere illustrated by the ECMWF 30hPa sequence shown below may lead to an extension of “Winter” into early March due to increased chance of blocking and colder surface winds from an Easterly point.

030218SSW30hpa

This change may have been predicted by UKMO contingency forecast for February which suggested a colder and drier than normal February. Cansips (issued 31st Jan) hints at normal and locally colder temperatures for February. CFSv2 suggests colder and drier weather types for February and these may extend into the first half of March.

temprainseasonal

Forecast update.

The chance of a colder and drier February and start March for SW England is more likely than previously.

Caution.

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

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

References.

CFS2  info

Stratospheric Diagnostics from Free University Berlin

 

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

Published 18 December 2017.

1. Influences.

Changes in sea temperature.

sstanom141217

Apart from a little cooling, relative to “normal”, near the North of Scotland Atlantic anomalies continue to be above normal. The tropical area is forecast to remain slightly above normal as shown in the UK Met Office plot below (right). The La Nina in the Pacific is well established, with a large area of below normal sea temperatures in the eastern Pacific south of the equator. The La Nina is forecast to slowly decline during the Spring and early Summer as shown by the NMME plot below (left).

tropsst1

IRI published a statistical relationship between La Nina and UK rainfall and this is shown below for January to May, however, as the La Nina becomes weak so the statistical relationship may decline.

JFMMAMlaNinprobs

IRI probabilities of Wet /Normal /Dry seasons based on possible links to La Nina

The plots above suggest that SW England has slightly higher probabilities of Normal to Dry conditions as we move into Spring.

Another statistical relationship which may play a part in the remainder of the Winter and Spring seasons is the Quasi-Biennial Oscillation (QBO). The QBO is linked to conditions over Western Europe during late autumn and early winter through an influence on the phase of the North Atlantic Oscillation (NAO) at the surface. An easterly phase of the QBO tends to moderately increase the chances of a negative phase of the NAO, which in turn increases the chances of below-average temperatures.”

qbo

QBO monitoring data (shown above) indicates that the easterly (negative) phase of the QBO remains above 50hPa.

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) continues to oscillate between positive and negative phases with ensemble predictions of remaining in a positive phase through to the end of December. This maintains a signal for a  milder/wetter winter season to develop.

nao181217

The North Atlantic Oscillation can also be affected by the Madden-Julian Oscillation. In an early issue of the contingency forecast (15 December 2017), the Met Office states that “the Madden-Julian Oscillation is an area of enhanced thundery activity that moves eastwards through the tropics over a period of several weeks. It has recently been active and is currently in a location that frequently leads to a negative phase of the North Atlantic Oscillation about 10 days later. The negative phase of the NAO brings colder-than average conditions to the UK, implying an increased chance of colder than-average temperatures in early January.” For more information see Met Office NAO information.

The next statistical relationship to consider is the development of a sudden stratospheric warming. Should this occur there can be an impact on the Jet stream causing it to weaken and allowing High pressure to develop over Europe. This could bring colder temperatures further west and possibly into the UK.

The stratospheric polar vortex has been displaced eastwards over recent weeks by a series of warming events across the N Pacific and into Canada, as can be seen in the temperature plot for the North Pole.

pole30_nh

It is not clear whether there will be a full disruption of the polar vortex, though this remains a risk, possibly leading to an upset in the model forecasts. Several of the seasonal models are able to handle changes in the stratosphere.

30hpa

ECMWF 30hPa chart 17 December and forecast for 27 December 2017

Analysis and Numerical (model) output.

A: Recent Climatology.

tandr181217Nov

Temperatures across the SW of England have been near normal and for many areas it has been a fairly dry period. Recent reservoir levels remain above normal for the time of year, but further dry weather may impact the storage levels for the winter as a whole.  River flows in the region for the Autumn season show western areas above normal and eastern areas below, although November data shows reduced river flow in more areas.

riverflowsNov2017

The  full summary is available from the Hydrological Summary  –  November 2017 summary PDF 

An experimental product from the Global Flood Awareness System suggests the flood risk areas for the next 4 months based on ECMWF seasonal forecast.

181217riverflow

Hint at below normal river flows in Somerset and high flows in the Exe estuary, the latter looking odd. Compared to the previous forecast there is a lower probability of flooding in some Wales and N England.

B: Upper Troposphere:

z200JFM1117

CFS2  200hPa monthly mean Jan Feb March 2017 and anomalies (lower)

z200MAM1217

CFS2 200hPa monthly mean contour March April May 2017 and (lower) anomalies

CFS2 forecast for 200hPa suggest above normal heights across the UK but still with a signal for enhanced jet across the Atlantic in February.

C: Lower Troposphere:

Comparing the CFS2 mean of 10 days forecasts (top row of each pair temperature anomaly, lower row indication for above or below normal rainfall (reds are above).

cfandnmmjfm2017

Jan Feb March 2017 temperature and precipitation anomalies

cfandnmmmam2017

March April May Temperature and rainfall anomalies

The main theme from the above is for above normal temperatures and a wet period early in 2018 but a drier Spring with temperatures nearer normal, for at least some of the months.

D: Comment:  Seasonal temperature and rainfall forecast data for the Autumn have tended to over forecast above normal temperature and rainfall. There has been some indications of below normal rain in southern areas but these have not been consistent. Forecasts of below normal temperature seem to be rare in the model output. So far in December temperatures have been near or slightly below average and the rainfall about half of the total for a normal month but this can easily change. Verification summary.

2. Forecast.

Remainder of Winter ( 2018  January and February) :

There remains a strong indication for a milder than average January and February in the SW of England  This does not rule out some colder spells, probably with North or NW winds rather than easterly, but suggests that the cold spells will be short lived.

Rainfall is uncertain month to month but the suggestion that mobile westerly patterns will come to dominate the weather patterns suggests above normal  rainfall especially in Cornwall and to the west of the moors. Elsewhere near normal or even slightly below normal rainfall seems possible, perhaps with January being the wetter month. The snow risk is reduced compared to average with little if any snow for lower ground but some snow for the moors.

Due to the statistical relationships, outlined in part 1, there is a moderate risk that colder and drier weather may develop making this forecast summary uncertain.

Winter Climate: 1981-2010 average temperature values for lowland areas 7°C in the West and 5°C in the East. Rainfall;  January 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):

Temperature probably slightly above normal for the season but possible colder periods in March and again in May. Rainfall near normal in the west, elsewhere drier 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.

Summer 2018  (June July August). Limited model data:

Temperatures near normal, perhaps a cooler start and a warmer end to summer compared to average. Uncertain rainfall but perhaps above normal in June and near normal later.

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

3. Caution.

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

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

4. References.

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

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

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

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

CFS2  info

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

Stratospheric Diagnostics from Free University Berlin

 

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

Published 18 November 2017.

1. Influences.

Changes in sea temperature.

161117ssta

Positive temperature anomalies (shown in the image above for the 16th November) are most marked in the North Atlantic south of about 50 degrees North but are less marked towards the equator. Consequently winds from a generally SW direction are likely to be milder than average, at least for the next month or so.

La Nina is evident in the Pacific and forecast to remain as a fairly weak La Nina through to Spring or Summer 2018.

Nino3.41117

NMME ENSO area 3.4 ensemble and (right) UKMO tropical N Atlantic ensemble

IRI statistical relationship between La Nina and UK rainfall for the winter is shown below. La Nina is weak so influence may not be strong but many of the seasonal model forecast hint at wetter in north and drier in south –  see models section below.

La Nina

Winter season precipitation probabilities during La Nina events.

Other statistical relationships may play a part in the Winter and Spring seasons, for example according to the Met Office late October Seasonal Forecast; “the Quasi-Biennial Oscillation (QBO), an oscillation of the equatorial winds in the stratosphere, is in an easterly phase. The QBO is linked to conditions over Western Europe during late autumn and early winter through an influence on the phase of the North Atlantic Oscillation (NAO) at the surface. An easterly phase of the QBO tends to moderately increase the chances of a negative phase of the NAO, which in turn increases the chances of below-average temperatures.”

QBO monitoring data is shown below along with the 50hPa ECMWF analysis on the 17th. Minimal warming is shown during the subsequent 10 days in the forecast at 50 and 30hPa.

QBO

Left QBO monitoring (left )shows negative phase descending in the stratosphere. ECMWF analysis at 50hPa shows the well established winter polar vortex and minimal warming.

North Atlantic Oscillation monitoring using 500 hPa is shown below and includes a forecast for the next season. NCEP ensemble forecast suggest NAO may move into negative phase later in November and for much of December. Consequently increased chance of blocking patterns which could be cyclonic or anticylonic over the Uk area.

For more information see Met Office NAO information.

nao.sprd2

Analysis and Numerical (model) output.

A: Recent Climatology.

Following on from a couple of unsettled wetter months, October / early November was drier and milder than average across the SW of England. Recent reservoir water levels remain above normal for the time of year, although Wimbleball was only at 55% of capacity at the time of writing. River flows in the region show western areas above normal and eastern areas below with groundwater in eastern parts of Devon and Dorset at notably low levels.. The  summary is available from the Hydrological Summary  –  October 2017 summary PDF 

A new experimental product from the Global Flood Awareness System suggests the flood risk areas for the next 4 months based on ECMWF seasonal forecast. Hint at below normal river flows in Somerset and high flows in the Exe estuary which looks odd.

FloodriskNDJF

B: Upper Troposphere:

CFS2 forecast for 200hPa suggest above normal heights across the UK but with below normal heights to the north suggesting increased zonal types (unsettled systems from the west) with February heights below normal across the north of the UK.

z200DJF1117

200hPa CFS2 forecast mean for 2017 December, 2018 January and February

C: Lower Troposphere:

Only BCC China seasonal forecast suggest below normal temperatures this winter and it is often a little cooler than other centres. The main signal from almost all seasonal forecasting centres is for above normal temperatures this winter. Highest anomalies appear to be in the S and E of the UK.  NMME and CFS2 winter season graphics are shown below.

nmmewinter

NMME temperature anomaly (top) and rain rate indicator (lower row)

DJF131117CFS2

CFS2 mean of 10 days output. Monthly mean temperature and rain rate anomaly (winter)

Probably worth noting that the multi-model ensemble tends to be a little warm and that rainfall forecasts in general are not good with month to month detail. Despite a warm signal colder spells are still possible – see for example temperature plot from a single CFS2 model run.

Exeter1117

Temperature forecast for Exeter area to August 2018

NMME plots for spring 2018 continue with a mild theme but note the much drier signal.

nmmespring

D: Comment:  Seasonal temperature and rainfall forecast data could have been better recently but 2016 data suggets data in November might fare better Verification summary.

2. Forecast.

Winter (2017 December, 2018  January and February) :

There remains 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.  The suggestion that temperature anomalies could be lower early in the winter and higher later can again be seen in the latest model data. This suggests that the temperature in December may be nearer normal but with milder months to follow.

Rainfall is uncertain month to month but the suggestion that mobile westerly patterns may bring cloud and rain suggest above normal  rainfall especially in Cornwall and to the west of the moors. Elsewhere near normal or even slightly below normal rainfall seems likely, perhaps with January being the wetter month. 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):

Temperature probably slightly above normal for the season but close to normal in April. Rainfall near normal in west elsewhere drier 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

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

Stratospheric Diagnostics from http://www.geo.fu-berlin.de/en/met/ag/strat/produkte/winterdiagnostics/index.html

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