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

Published 18 June 2019.

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1. Influences.

Changes in sea temperature.

170619ssta

Due to the recent unsettled and rather cool weather the sea temperature around the UK (and western Mediterranean Sea) is mostly a little below the average along with much of the North Atlantic (40 to 55North).

Tropical Atlantic seems to be warming and is forecast to remain warmer than average – see Met Office graphic below:

tna_anom_20190601

In the Pacific weak El-Nino conditions have continued and are expected to persist as indicated by CFSv2 and NMME multi model ensemble forecast (shown below).

180619nino

The North Atlantic Oscillation index (shown by a 500hPa index in the image below) returned to slightly positive from mid April after the first negative phase period for some time but shortly after went and remained negative. For the summer period this translates to a colder/wetter phase for the UK.

180619nao

NAO background information see the Met Office NAO information.

Recent Climatology

In the SW of England, June  has been wetter, colder and cloudier than average. Main station SYNOP data to the middle of June showed the average temperature anomaly to be around minus 1 C with rainfall between 20 and 50% above average and sunshine only a third of average. This represents a significant change from overall warmer and drier weather of the last six months. Seasonal models historically have been poor at picking out a change to colder types.

170619temphist

Winter and Spring temperatures have been above normal and rainfall mostly normal or below across SW England.

170619rainhist

River flows were showing below normal values in the east of the SW Region although groundwater seems near normal in the May report. The wet weather in June is likely to lifted river levels somewhat.

170619riverflowmay

Full details can be found in the  May 2019 Hydrological summary PDF 

The reservoir levels in the SW of England (16th June) show 80% storage which is slightly below the normal June level, but recovering.

060619reslev

The June experimental product from the Global Flood Awareness System (Version 2) was not available on the 18th.

Atmosphere predictions.

A:  1: Stratosphere 

17061950hpa

Remains in summer mode as shown by the ECMWF 50hPa chart for 17th June 1200UTC.

A 2: Upper Troposphere

CFSv2 200hPa monthly mean forecast height (contours) and anomaly (lower row) for the period July to November 2019 based on 7th June data, show mostly above normal heights but perhaps imply a slightly enhanced jet in mid Atlantic during October and more especially in November though perhaps to west of Uk.z200SON0619

B: Lower Troposphere:

July to September 2019 solution in low resolution from WMO . JAS and individual months. Top row temperature anomaly, mid row precipitation anomaly and lower row PMSL anomaly.

White areas are area where the probabilities of below/normal/above are similar hence there is no overall signal for this period from the WMO super ensemble which includes DWD, CMC, BoM, Moscow, Seoul, CPTEC, UKMO, Washington, Pretoria, Tokyo, ECMWF, Beijing and Toulouse seasonal models.

WMOJAS062019

WMO July to August

UKMOJAS062019

UKMO JAS and monthly anomalies

nasa0619

NASA June 2019 to Feb 2020 Temp and Rain anomaly

nmme1

NMME July to November 2019 top row temperature lower row rain rate anomaly.

NMMEDJF06


NMME December 2019 to Feb 2020 top row temperature lower row rain rate anomaly.

There are several models that suggest colder and wetter summer but not the majority.

A summary from all the models for July to September looks roughly:
Temperature: 50% above normal, 31% normal 19% below normal.
Rainfall:  50% above normal, 28% normal, 22% below normal.

Additional model graphics can be seen at the seasonal forecast summary

C: Recent results for the Spring (March to May 2019):

Most models forecast above normal temperatures but NCEP, CANSIPs and JMA captured the trend for a less mild May.
Precipitation: Good indication that March could be wetter and some idea that the season could be wetter in places but was incorrect about the south/SW. Signal for below normal in places was correct but as usual exact location was not predicted well.

Comparison graphics can be seen at the verification page for Spring 2019

2. Forecast. SW England.

Remainder of Summer 2019  (July August) 

A warmer than average summer for the season is still more likely than not despite a colder two thirds of June.

Overall the balance has shifted towards above normal rainfall for the season.Models remain mixed at which month could be drier or wetter. However some longer dry spells seem likely over the next two months.

Higher temperatures may lead to shorter periods of heavier rain but fewer wet days which has been a pattern in recent years.

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 2019  (September October November) limited data. 

A warmer September, then milder than normal each month and for the season.  Still looks likely that the Autumn could start drier in September then end with a wetter November, hence overall average or below average rain for 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 2019  (December January February) minimal data. 

Milder than average throughout. Near or above average rainfall for the season. Below average snowfall more likely than above average.

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  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

International seasonal monthly data from WMO

Stratospheric Diagnostics from Japan Met Agency and Free University Berlin

Climate data from The Met Office UK and NCEP USA