Review and Experimental Long Range Forecast for SW England. October 2020.

Published 19 October 2020.

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1. Influences.

Changes in sea temperature

Atlantic equatorial sea temperatures remain warmer than climatology as is the area area around the UK, Norwegian Sea and Baltic.

Colder sea temperatures in the East Pacific just south of the equator show the La Nina has strengthened.

The tropical north Atlantic is forecast to remain slightly warmer than average through to at least March 2021 (See Met Office graphic below).

Wikipedia states that “The 2020 Atlantic hurricane season is an ongoing tropical cyclone season which has featured tropical cyclone formation at a record-breaking rate. So far, there have been a total of 27 tropical or subtropical cyclones, 26 named storms, 9 hurricanes, and 3 major hurricanes.[nb 1] With 26 named storms, it is the second most active Atlantic hurricane season on record, behind only the 2005 Atlantic hurricane season. It is also only the second tropical cyclone season to feature the Greek letter storm naming system, with the other season also being 2005.

Wikipedia track map so far in 2020

The most recent storm (October 5th to 12th) Hurricane Delta was the record-tying fourth named storm of 2020 to strike Louisiana, as well as the record-breaking tenth named storm to strike the United States. “

A new storm shown “Epsilon” is likely to track near to Bermuda on the 23rd/24th of October 2020.

In the Pacific, sea temperatures continue to trend towards cooler / La Nina conditions which may now last until early Summer Spring 2021 before returning to neutral conditions.

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) turned negative in near the end of September but is forecast to below positive before the end of October.

The positive NAO phase represents a stronger than usual difference in pressure between the two regions. Winds from the west dominate, bringing with them warm air, while the position of the jet stream enables stronger and more frequent storms to travel across the Atlantic. These support mild, stormy and wet winter conditions in northern Europe and eastern US. Conversely, northern Canada, Greenland and southern Europe are prone to cold and dry winter conditions.

For Met Office information about the NAO see https://www.metoffice.gov.uk/weather/learn-about/weather/atmosphere/north-atlantic-oscillation

Recent Climatology –  SW England

October to the 18th: Temperatures have been averaging around 11 Celsius or between 0.5 and 1 Celsius BELOW the 30 year average. Rainfall shows between 50 and 80% of the average, thanks mostly to the four wet days at the start of the month and mainly the 2nd and 3rd. Sunshine has so far been and near or slightly below average.

This follows drier than average September and a wetter summer with generally near normal temperatures.

River flows in September 2020 were near or slightly below normal across the SW and groundwater levels were also near normal in the eastern parts of SW England. Details can be found in the September 2020 Hydrological summary PDF 

The reservoir levels in the SW of England (16th August) were above average as of the 11th of October.

Global Flood Awareness System. October forecast for Oct to Jan has above normal flood risk for much of the UK and Ireland. (Orange below normal Blue above).

Details of soon to be implemented improvements to the system can be found the the following URL https://www.ecmwf.int/en/about/media-centre/news/2020/new-upgrades-deliver-step-change-improvements-flood-forecasting

Atmosphere: Predictions.

A:  1: Stratosphere

Stratosphere polar vortex is forecast to strengthen towards winter mode as shown by the ECMWF 30hPa height and temperatures for October 18th 1200UTC and forecast chart for 28th October 2020.

A: 2: Upper Troposphere

October 6th data for CFSv2 200hPa contours for November 2020 to January 2021  shown in top row along with the anomalies from CFS (middle row) and the NMME anomalies (lower row). Forecast is for above normal heights but with an increase in jet flow during January.

B: Lower Troposphere:

A selection of  November solutions using October 2020 data are shown below.

Top row temperature anomaly and lower row precipitation anomaly. 

CFS2 NASA ECMWF NMME for November 2020
WMO ensemble data for November 2020 : WMO BoM CMC and DWD
WMO ensemble data: Beijing Moscow Exeter and Toulouse 

A selection of  December to February (winter) solutions using October 2020 data are shown below.

Individual months, top row temperature anomaly and lower row precipitation anomaly. 

NMME DJF
NASA DJF
ECMWF DJF
CFS2 E3 data DJF
WMO super ensemble DJF
Beijing
BoM Melbourne
DWD Germany
Montreal Canada
UKMO
Toulouse MF
Korea KMA

C: Comparing the output of seasonal models for July August September 2020, based on June  2020 data.

For graphics and details see Verification review 2020 Jul Aug Sep

Temperature forecast for the three months had the correct idea even the suggestion of the colder and warmer areas

Rainfall: The idea that the south could see one wetter month was correct and there were hints to wetter than average in places but overall not an especially helpful forecast

Models monthly:
Temperature: ECMWF BOM CMC TOKYO and Washington(WMO) had some idea of the cold July and warmer August.
Rainfall: NMME UKMO and CMC had hints at parts of the correct sequence

Scoring for three month season (from text if available) will attempt to state good, fair, poor or no signal.

Despite some models scoring good few had the monthly sequence anything light right.

1. Russia: Temp good. PPN no signal.
2. USA – CFS2 : Temp fair. PPN fair .
3. UKMO Contingency: Temp good. PPN good .
4. UKMO : Temp good. PPN mostly no signal . PMSL poor
5. USA – IRI : Temp no signal. PPN .
6. KMA APCC : Temp good. PPN no signal.
7. JMA : Temp good. PPN good. PMSL good.
8. NMME : Temp good. PPN poor.
9. WMO : Temp good. PPN poor .
10. BCC : Temp good. PPN fair .
11. NASA: Temp good. PPN poor .
12. Brazil:
13. CanSips : Temp fair. PPN fair .
14. IMME: Temp good. PPN fair .
15. Copernicus Temp good. PPN poor . PMSL fair
16. EC Temp good. PPN poor . PMSL poor
17. MF Temp good. PPN poor . PMSL poor
18. JAMSTEC:
19: ECMWF (monthly) Temp: fair. PPN poor
20: CMCC Temp good. PPN poor . PMSL good
21: DWD Temp poor. PPN poor . PMSL fair

2. Forecast. SW England.

Remainder of  Autumn 2020 (November) 

Temperatures are likely to be near or slightly above the 30 year average (1981-2010)

Rainfall more likely to be slightly below normal than above across SW England (confidence low)

November climate: 1981 to 2010 average mean temperature 8 or 9C°C.  Average 1981 to 2010 rain 60 to 100mm East of the moors, 100-200mm west of the moors but over 250mm over the moors.

Winter (2020 December 2021 January February).

A milder than average Winter in indicated as well as each month being near normal or milder than average in most of the data. There is, however, a chance that December could be very close to average and a smaller risk that February could be a little colder than average.

Mixed rainfall indications with some of the wetter model solutions being cancelled out buy the drier ones in the WMO super ensemble. Overall though it seems more likely that total Winter rainfall may end up above average. There is a signal for the first half of Winter to be drier than average but the latter part could be much wetter than average and this may lift the overall winter total to be above average although the number of rain days could be below average. Below average snowfall seems likely – snow most likely confined to higher 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  (2021 March April May) limited data.

Milder than average temperatures seem likely for the season although March and April could see values closer to normal and May could be significantly milder than average.

Rainfall near or a little below average for the season although March 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 can be seen at  here.

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. 20146(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

International seasonal monthly data from WMO

Stratospheric Diagnostics from Japan Met Agency and ECMWF via  Free University Berlin

Climate data from The Met Office UK and NCEP USA

Review and Experimental Long Range Forecast for SW England. September 2020.

Published 19 September 2020.

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

Atlantic equatorial sea temperatures remain warmer than climatology as is the area area around the UK, Norwegian Sea and Baltic. Higher than average sea temperatures in the Gulf of Mexico, apart from the cool area near the NW coast of Florida (due to storm Sally) may aid the development of current potential storm “Beta”

Colder sea temperatures in the East Pacific just south of the equator show the La Nina has strengthened.

The tropical north Atlantic is forecast to remain slightly warmer than average through to at least February 2021 (See Met Office graphic above).

Wikipedia states that “The 2020 Atlantic hurricane season is an ongoing tropical cyclone season that has featured tropical cyclone formations at an unprecedented rate. So far, it has featured a total of 24 tropical cyclones, 23 named storms, eight hurricanes, and two major hurricanes.[nb 1] With 23 named storms, it is the second most active Atlantic hurricane season on record, behind only the 2005 Atlantic hurricane season. It is also only the second tropical cyclone season to feature Greek letter named storms, with the other season again being 2005.

Wikipedia track map
Images and time line from Wikipedia

In the Pacific sea temperatures continue to trend towards cooler / La Nina conditions which may now last until mid to late Spring 2021 before returning to neutral conditions.

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) turned positive at the start of August and heralded the drier and warmer weather. The index turned negative in mid August a forerunner of more unsettled and cooler weather. The positive phase is forecast to come to an end by in the last week of September as Atlantic mobility returns.

Recent Climatology –  SW England

September to the 19th: Temperatures have been averaging around 16 Celsius or between 1.5 and 2 Celsius above the 30 year average. There has been above average sunshine and rather low rain totals – typically less than 10mm recorded so far.

This follows an average to slightly warmer summer – June and August were warmer but July was slightly colder than average. It was also a very wet summer in terms of rain total, although July was drier in SW England.

River flows in August 2020 were above normal across the SW and groundwater levels were also above normal in the eastern parts of SW England. Details can be found in the August 2020 Hydrological summary PDF 

The reservoir levels in the SW of England (16th August) were above average as of the 13th of September.

Global Flood Awareness System. August forecast has above normal flood risk for the UK except perhaps inn the south. (Orange below normal Blue above).

Atmosphere: Predictions.

A:  1: Stratosphere

Stratosphere is transitioning towards winter mode as shown but the ECMWF 50hPa height and temperatures for 18th 1200UTC and forecast chart for 28th September.

A: 2: Upper Troposphere

CFSv2 200hPa contours for October to December 2020  shown in top row along with the anomalies from CFS (middle row) and the NMME anomalies (lower row). Forecast of above normal heights more especially in the over western Europe in November and indication of stronger contrast in the north Atlantic in December.

B: Lower Troposphere:

A selection of  October to December solutions using September 2020 data are shown below. Three month season and individual months, top row temperature anomaly and lower row precipitation anomaly. 

NMME
ECMWF
CFS2
NASA

Selection of WMO data including the WMO super ensemble. Full set from http://www.weather-info.co.uk/wxsvc/seaslatest.html

WMO super ensemble probability
UKMO
BoM Australia
BCC China
Brazil
Tokyo
Moscow

For the Winter period December 2020 to February 2021.

NMME
CFS2
ECMWF
NASA
WMO super ensemble

For Spring 2021, March 2021 to May 2021.

NMME
NASA

C: Comparing the output of seasonal models for May June July 2020, based on April  2020 data.

For graphics and details see Verification review 2020 Jun Jul August

Comment: 040920 The idea that June and August would have the higher warmer anomalies in the south was correct, but the rain forecast was poor except perhaps for August in the south.

Scoring attempts to state good, fair, poor or no signal for the three month as a whole.

Comment 040920: Monthly data did not imply the correct temperature sequence in any model – several models got the idea of less rain in the south in July.
Season: Temp: To be correct near normal but above across Midlands and E/SE England and parts of W Scotland. Rain: needed to show above average rain except N Scotland and SE England.
1. Russia: Temp poor. PPN fair.
2. USA – CFS2 : Temp fair. PPN poor .
3. UKMO Contingency: Temp good . PPN fair .
4. UKMO : Temp fair . PPN Good for N and SE elsewhere poor . PMSL poor
5. USA – IRI : Temp good . PPN fair .
6. KMA APCC : Temp good . PPN poor/no signal .
7. JMA : Temp good . PPN poor . PMSL poor
8. NMME : Temp good . PPN poor .
9. WMO : Temp good . PPN poor .
10. BCC : Temp good . PPN poor .
11. NASA – Temp good . PPN fair .
12. Brazil:
13. CanSips : Temp good . PPN poor .
14. SAWS: :
15. Copernicus Temp good . PPN poor . PMSL poor
16. ECMWF Temp good . PPN poor . PMSL poor
17. MF Temp good . PPN poor . PMSL poor
18. JAMSTEC: Temp good . PPN poor .
19:
20: CMCC Temp poor . PPN poor . PMSL poor
21: DWD Temp fair . PPN fair . PMSL poor

2. Forecast. SW England.

Remainder of Autumn 2020 (October November) 

Temperature are likely to be near or slightly above the 30 year average (1981-2010) October could see values closer to the average than in November.

Rainfall forecast lately have been poor and continue to be split for this period between drier and wetter solutions roughly 40% wetter/drier and 20% near normal. The start of October seems likely to be unsettled and rainfall for the month may well be near normal (wetter in the N of UK). November also probably near or a little above normal rainfall.

Autumn climate: 1981 to 2010 average mean temperature 11 or 12°C but nearer 10°C in rural areas. Maximum temperatures average 14 to 16°C. November normally colder than October. Autumn 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. October and November have similar number of rain days and totals range from around 70mm east of the moors to over 200mm over the moors.

Winter (2020 December 2021 January February).

A milder than average Winter in indicated as well as each month being near or milder than average. Caution models tend to be poor at picking colder types.

Mixed rainfall indications but Winter probably having above average rainfall and below average snowfall. There is a stronger signal for December being wetter than average compared to other months but February could also be wetter than average which is at odds with the data a month ago and illustrates the uncertainty. Below average snowfall seems likely – snow most likely confined to higher 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  (2021 March April May) limited data.

Milder than average temperatures seem likely for the season although March and April could see values closer to normal. Rainfall possibly below average in March but above in other months, hence above average for the season.

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 can be seen at  here.

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. 20146(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

International seasonal monthly data from WMO

Stratospheric Diagnostics from Japan Met Agency and ECMWF via  Free University Berlin

Climate data from The Met Office UK and NCEP USA