For more context and background information please read:
"Winter 2017/18 weather, Forecast pointers" issued on July 25th 2017
"UK winter 2017/18 - Update 2", issued 13th September 2017
"Winter 2017/18 - Update 4", issued 18th November 2017
The information here is intended to provide an update on developments.
September brought spells of wet weather and the Central England Temperature (CET) finished 0.2C below the average. When producing the winter forecast the September weather patterns are considered. A cool and cyclonic month is counted as a weak factor in favour of a colder winter. It is important to emphasise that a correlation between warm Septembers and milder than average winters is not accepted by many, but the TWO view is that it has existed in recent decades.
October has been a mild month with mixed conditions. Storms Ophelia and Brian brought disruption but there has also been a good deal of quiet and benign periods. The CET to the 29th is a mild 2.2C above the average. The October weather patterns will be counted as a weak factor in favour of a colder winter.
The picture from seasonal models which cover December, January and February is more mixed.
UK Met Office GloSea:Milder and wetter than average favoured.
JamstecMilder than average, especially in the south. Drier than average.
IRINo signal for temperature (meaning all outcomes are equally likely). Weak signal for a drier than average season in the north west and south east.
CFS v2Mixed but current updates hint at the possibility of colder conditions in January and February. (Check the latest CFS v2 charts on TWO).
The Russian and Chinese seasonal models suggest an increased chance of cold conditions.
The key things to note since the last update are:
GloSea is consistent.
Jamstec suggests a milder than average season in all of the UK and a drier one too.
IRI strongly favours an anomalously mild winter in Greenland. That often means an increased likelihood of cold weather in western Europe.
Note: The skill level of seasonal models for the UK and north western Europe remains low. In other words they are not very accurate.
See the July update for more background information.
Possibly close to neutral this winter. That suggests a reasonable chance of colder outbreaks.
The QBO is currently in a negative (easterly) phase and that is expected to continue through the rest of the autumn and winter. If that is the case the chance of a colder winter would be slightly increased.
La Niña conditions are favored (~55-65%) during the Northern Hemisphere winter 2017-18. If that is the outcome the chance of a colder than average winter would be increased.
Since the last update activity has been low but the next solar minimum is not expected until 2019 or 2020. There is a suggestion that colder winters are more likely to occur in the UK shortly after a solar minimum is reached. However a "quiet" sun arguably leads to an increased chance of colder winters.
It remains too early for a clear signal for winter 2017/18 to emerge. However the TWO view is that since the September update the chances of colder than average conditions have increased. Another update will be published in mid-November but at this stage the TWO view is the chance of a colder winter is significantly higher than in recent years.
Regular updates will be issued before the TWO winter forecast is released at the end of November.
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