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Winter 2019/20 update 3


04/11/2019

Overview

For more context and background information please read:

Winter 2019/20 weather, Long range forecast signals issued on July 30th 2019

UK winter 2019/20 Update 2 issued on September 13th 2019

Berkhamsted railway station

September and October

The first eight months of the year recorded an average or above average Central England Temperature (CET). Summer 2019 was warm, although more mixed than last year's. Despite that, the UK's hottest day was recorded on Thursday 25th July when 38.7C was reached at Cambridge Botanic Garden.

September continued the trend. The CET finished 0.7C above the 1961-1990 average which is the period for comparison recommended by the WMO (World Meteorological Organisation). TWO considers a warmer than average September to be a factor supporting a mild winter in the UK.

The pattern was broken in October. The month was very wet and the CET finished 0.6C below the average. Therefore it was the first cooler than average month of the year. This will be considered neutral when producing the winter forecast.

If November goes on to be cooler and wetter than average it will be considered as a factor favouring a colder winter.

Seasonal models

Most of the long range computer models continue to suggest a milder than average winter in the UK. However, since the last update the level of uncertainty has increased with some models hinting at a colder outcome.

Model Temperature Precipitation
UK Met Office GloSea (UK) D/J/F Above average Above average
Meteo France (France) D/J/F Above average in the north and west Above average in the north west. Below average in the east.
ECMWF D/J/F Above average Mostly above average
DWD (Germany) D/J/F Above average in the north Mostly no anomaly
International Research Institute (IRI) D/J/F No anomaly Below average
Jamstec (Japan) D/J/F Below average Below average
C3S multi system (European combi) D/J/F Above average Above average in the west
CFS v2 (USA) D/J/F Close to average  Close to average
BCC (China) D/J/F Above average Above average

 

D/J/F = December, January, February

The Climate Forecast System v2 is available on TWO. View the latest CFS v2 charts.



Indexes and teleconnections

See the July update for more background information.

North Atlantic Oscillation (NAO)

This year the likelihood of a neutral NAO is considered to be higher than the norm.

Quasi-biennial oscillation (QBO)

The QBO switched to a positive phase in November 2018. The mean period of each phase is 28 or 29 months, so there is a high likelihood of it staying positive through the winter. If that happens, it would be a factor supportive of a milder winter.

Berkhamsted melting snow,  March 2018

El Niño Southern Oscillation (ENSO)

Forecasting the ENSO conditions several months ahead is prone to error, but at the moment El Nino is favoured to remain neutral through the Northern Hemisphere winter.

Solar Activity

The coming winter is expected to coincide with the minimum in Solar Cycle 24. Thereafter activity is expected to steadily recover as Solar Cycle 25 begins.

Northern hemisphere snow cover

Snow cover is currently above average in Eurasia and North America. That suggests an increased chance of high pressure blocks forming at high latitudes. That can often lead to the displacement of cold air down to mid latitude locations such as the UK. Therefore this variable currently counts as supportive of a colder winter.

Summary

Since the last update the signal for a mild winter has faded to an extent. Output from some of the seasonal models has become more nuanced. Also the above average level of snow cover in parts of the Northern Hemisphere suggests an increased chance of colder periods in mid latitude locations.

Therefore a clear signal for winter 2019/20 has still not emerged. At this stage the TWO view is the evidence still weakly favours a mild winter. However, there is a chance of a the balance switching this month.

Regular updates will be issued before the TWO winter forecast is released at the end of November.

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