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

Published 19 June 2018

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

1. Influences.

Changes in sea temperature.

anomnight.6.14.2018

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

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

ecenso0618

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

sea1062018

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

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

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

NAO062018

For background information see the Met Office NAO information.

Recent Climatology.

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

tandr0618

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

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

soil4

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

riverflow0618

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

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

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

glofas062018

Atmosphere predictions.

A: Upper Troposphere

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

cfs2z2000618

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

cfs2z200son0618

B: Lower Troposphere:

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

July August and September 2018.

nmmejas0618

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

e3jas0618

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

ECJAS062018

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

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

September October November 2018.

e31son

CFS2 E3 version data 7 June

e3son0618

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

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

nmmeson0618

NMME Sept Oct Nov 2018 (Lower row Blue drier)

ECSON062018

ECMWF September October November (Lower row Blue wetter)

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

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

C: Recent results/comments:

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

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

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

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

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

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

2. Forecast.

Remainder of Summer 2018  (July and August). 

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

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

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

Summer climate: 1981 to 2010 average daily mean temperature 14 or 15°C in many areas to 16 or 17°C in main urban areas also locally east of the moors and more widely in Somerset. Maximum temperatures average 19 to over 21°C in similar areas. July often warmer than August. Average 1981 to 2010 rain in July typically 60 to 80mm, but 40 to 60mm in places especially East of the moors and in Somerset. Locally over 100mm across the moors. August slightly small areas with the lower rain totals due to July often being drier than August.

Autumn 2018  (September October November) early indications. 

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

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

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

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

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

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

3. Caution.

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

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

4. References.

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

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

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

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

CFS2  info

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

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

ECMWF seasonal monthly data from weather.us

Stratospheric Diagnostics from Free University Berlin

Climate data from The Met Office UK and NCEP USA.

 

Advertisements

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s