Review and Experimental Long Range Forecast for SW England. Feb 2019.

Published 23 February 2019 slightly later than normal.

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1. Influences.

Changes in sea temperature.210219sst

The sea temperature around the UK and across much of the North Atlantic is fairly close to the seasonal normal, a shade warmer/cooler in places.

The Met Office diagnostic for the tropical Atlantic (shown below) was near normal with a trend to above normal values in the majority of the ensemble solutions.

tna_anom_20190201

In the Pacific weak El-Nino conditions have established, see CFS2 and  multi model ensemble forecast below.

nino

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) has been slightly positive (warmer wetter phase for UK) since early January and the index is likely to remain in a positive phase over the short term.

nao

For NAO background information see the Met Office NAO information.

Recent Climatology

In the SW of England February main station SYNOP data to 0600 23rd February shows the average temperature anomaly at between +1.6 and +1.9 C, rainfall at around 70% of average and about 90% of normal sunshine hours.

December 2019 was milder than average, January 2019 saw close to normal temperatures and so far February has been mild resulting in a milder the average “winter” (DJF).oct-jan

 

November and December 2018 were wetter than average across the SW but October 2018 and January 2019 were drier. So far February has been slightly below normal so that winter looks like ending up slightly drier than average across the SW

raintempclimat

Rover flows in SW England during January reflect the recent dry weather with eastern parts of the region showing lower longer term values.

juntojanriverflow

ground

Ground water levels for eastern parts of SW England remain near normal.  Full details can be found in the  January 2019 Hydrological summary PDF 

The reservoir levels in the SW of England (17th February) show 84% storage which is below the normal winter level.

17219res

The experimental product from the Global Flood Awareness System (Version 2) based on early February ECMWF seasonal forecast for March to May 2019. The system does not suggest enhanced flood risk for UK currently. To date this system has not be a useful guide.

glofas

Atmosphere predictions.

A:  1: Stratosphere 

A sudden stratospheric warming (SSW) took place during December and JMA issued a STRATALERT on the 21st of December The warming became MAJOR and continued into January. An END message was issued bu JMA on the 4th February.

sswend040219

It appears that as far as the UK was concerned the warming did not fully extend down trough the atmosphere or perhaps the blocking pattern and High pressure location was not conducive to a colder easterly but maintained a milder S or SW flow.

A discussion on SSW evolution by Simon Lee is of interest Full text by Simon Lee December 2018

Since the end of the warming the stratosphere has returned to nearer normal conditions with stronger zonal westerlies becoming established. GFS 10 hPa zonal wind had shown a reversal but recent forecasts show a return to westerly types. Graphic below H Attard, Albany NY

hattardzonal

At 10hPA a strong polar vortex has established and at 50hPa the ridge/block pattern is due to collapse in favour of a zonal type. A final warming (end of winter type) is not yet indicated in the 10 day ECMWF stratospheric forecast.

strat10and50

CFS2 climate model 10hPa polar vortex in March becoming the summer pattern in April 2019.

10hpacfs2

A 2: Upper Troposphere

CFSv2 200hPa monthly mean forecast height (contours) and anomaly (lower row).

cfs2200mam

March April May 2019 200hPa month mean and anomaly

Some indication of enhanced jet in March to W of UK and less extent for a SSW jet in April and May possibly steering lows further N over or to N of UK on average. More generally ridged pattern for June and  August and in general above average heights throughout the forecast.

cfs2e30219jja200hpa

June July August 2019 200hPa month mean and anomaly

B: Lower Troposphere:

B1: Spring 2019

Selection of Spring (March April May) solutions. Top row temperature anomaly and lower row precipitation anomaly.

wmomulti0219mam

WMO multi model ensemble Spring 2019. (MAM and monthly anomalies) 

ukmo0219mam

UKMO Spring 2019 (MAM and monthly anomalies)

nmme0219mam

NMME multi model ensemble

cfs2e3mam0219

CFSv2 mean of 10 days output(E3 data)

ec0219mam

ECMWF Sprin 2019 (MAM and monthly anomalies)

Common signal for SW England, above average temperatures for season and for March to be wetter and in some models also April.

B2: Summer 2019

nmmeJJA0219

NMME multi model ensemble JJA monthly anomalies

cfs2e30219jja

CFSv2 E3 mean of 10 days runs. Monthly anomalies JJA

ECJJA022019

ECMWF JJA monthly anomalies

C: Recent results for the period November December January :

Most models got December being milder. EC looked a little cool but was good with trend and got the near normal January following milder December, other models not helping with this. EC PPN not so good for November and January. CFS and NNME overly strong PPN anomalies but hinting at wetter December and less so in January which was correct. 

2. Forecast. SW England.

Spring 2019  (March April May) 

Possibly near normal temperatures in March then trending to milder than average temperatures for the season. May probably the month with the strongest signal for above normal temperature although several models suggest April could be the relatively mildest month.

A wetter than average season is likely mainly due to rainfall in the first half of the season. The middle or perhaps the end of the season may well see nearer normal rainfall but there is little agreement in month to month rainfall detail after March.

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 2019  (June July August) 

Warmer than average summer but with temperatures in June nearer normal and August more likely to be much warmer than average.

A wetter start to summer in June but then drier than normal above normal rain although  there is some indication that June could be drier. Probably below normal rainfall for the season as a whole.

Chance of reduced river flows and reservoir levels causing some concerns.

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 2019  (September October November) limited data. 

Milder than normal monthly and for the season.  Could be a wetter than average start to Autumn in the SW but then near or even below normal rainfall possible for for October or November.

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

3. Caution.

Experimental Long Range Forecasts do not have a good success rate. The data used for the above forecast summary 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. 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.