As ever, it is important to remember that seasonal forecasting in the UK remains extremely challenging. The UK's location means that small changes on a global scale can have a very big impact on our weather.
The list below shows temperature anomalies in UK winters since 2008-09. The last significantly colder than average winter was 2010-11. In the UK there is a tendency for cold winters to come in small clusters, with the last one being between 2008 and 2013. Before that arguably it was 1978 to 1987, with only isolated cold winters in the interim period.
2008-09Colder than average. The UK mean temperature for the winter was 3.2°C, which is 0.5°C below average.
2009-10Much colder than average. The UK mean temperature for the winter was 1.6°C, which is 2.1°C below average. In many parts of the UK this was the coldest winter since 1978/79.
2010-11Colder than average. The UK mean temperature for the winter was 2.4°C, which is 1.3°C below average.
2011-12Milder than average. The UK mean temperature for the winter was 4.5°C, which is 0.8°C above average.
2012-13Slightly colder than average. The mean temperature over the UK for winter was 3.3°C, which is 0.4°C below average.
2013-14Much milder than average. The UK mean winter temperature was 5.2°C, which is 1.5°C above the average.
2014-15Close to average. The UK mean winter temperature was 3.9°C, which is 0.2°C above the average.
2015-16
Very mild. The third warmest in the series from 1910. The UK mean temperature was 5.5°C, which is 1.8°C above the average.
2016-17
Very mild. The UK mean temperature was 5.0°C, which is 1.3C above the average.
2017-18
Close to average. The UK mean temperature was 3.6°C, which is 0.2°C below average.
2018-19
Much milder than average. The UK mean temperature was 5.2°C, which is 1.4°C above average.
2019-20
Much milder than average. The UK mean temperature was 5.3°C, which is 1.5°C above average.
2020-21
Close to average. The UK mean temperature was 3.5°C, which is 0.2°C below average.
2021-22
Milder than average. The UK mean temperature was 5.2°C, which is 1.1°C above average.
2022-23
Close to average. The UK mean temperature was 4.3°C, which is 0.2°C above average.
2023-24
Milder than average. The UK mean temperature was 5.29°C, which is 1.49°C above average.
Last winter was mild. Although it brought a cold spell in middle January, the season was virtually snowless in much of the densely populated southern Britain.
A number of indicators are used when producing the winter forecast. The key ones are discussed below, but they could change through the rest of the autumn.
The seasonal models listed below all reach until the end of the meteorological winter.
D/J/F = December, January, February
The Climate Forecast System v2 is available on TWO. View the latest CFS v2 charts.
All of the models are favouring above average temperatures. The signal for precipitation levels as usual is much weaker, with a slight bias for wetter than average conditions in the north.
A likely scenario would be for a positive North Atlantic Oscillation (NAO) to dominate through the period. With pressure relatively high to the south of the UK, the wettest conditions would be in the north. It also suggests cold spells would be most likely to come from incursions of Arctic air (rather than a continental easterly flow), with the north at a greater risk than the south.
The NAO is essentially a measure of pressure patterns across the North Atlantic. During the winters when a negative NAO develops, blocking areas of high pressure form at high latitudes and displace the cold Arctic air down to mid latitude locations such as the UK.
This year the likelihood of the NAO going negative is expected to decrease as the winter progresses. Therefore, cold spells would be more likely during the first half of the season.
The QBO index is determined by the strength and direction of equatorial zonal winds in the tropical stratosphere. When the winds are in a westerly phase the index is positive and when in an easterly phase, it is negative. A correlation between the strength of the jet stream across the North Atlantic and the QBO has been identified. A negative (easterly) QBO favours a weaker jet stream which in turn means a greater chance of cold spells during the winter months.
The current expectation is for the QBO to be in a positive phase during the coming winter.
On balance this increases the likelihood of a milder and wetter than average winter.
El Niño takes place when Sea surface temperatures (SSTs) in the central-east Pacific are anomalously warm and La Niña, when they are colder than average. ENSO has an impact on global weather patterns, although the link to the UK is quite weak.
Forecasting the ENSO conditions several months ahead is prone to error, but at the moment there is a 71% chance of La Niña developing through the autumn and persisting through to March 2025.
La Niña correlates with an increased chance of cold spells during the first half of the winter. The likelihood of a more vigorous Atlantic flow and positive NAO, which suggest milder conditions, increases later on.
The SPV is a large area of low pressure and cold air that circulates around the Earth's poles in the stratosphere during winter months. It forms a swirling vortex of strong westerly winds that helps contain the cold air near the poles. A disrupted and weakened polar vortex can lead to outbreaks of cold air at mid latitude locations such as the UK.
Some computer models have suggested the SPV will be quite weak, at least early in the winter. That supports the idea of cold spells occurring more likely early on, relative to the norm.
The link between solar activity and the weather remains controversial. There is a suggestion that colder winters are more likely to occur in the UK close to or shortly after a solar minimum is reached.
Solar Cycle 25 is considered to have started between August 2019 and January 2020. It is expected to peak between late 2024 and early 2026.
The expected high levels of solar activity possibly increase the chance of a mild winter in western Europe.
The automated system checks the current state of the 500hPa level in the northern hemisphere and compares it with the same day for every year going back to 1948.
As of 5th October 2024, the 5 closest matches over the last 30 days are:
1) 2023
2) 1998
3) 2001
4) 2019
5) 2005
Winter 2023-24 was milder than average
Winter 1998-99 was milder than average
Winter 2001-02 was milder than average
Winter 2019-20 was much milder than average
Winter 2005-06 was slightly colder than average
Therefore, the analogue index at the time of publication is strongly favouring a milder than average winter. All of the best matches have occurred relatively recently, with none from the cold 1960 to 1990 period.
You can view the latest 30 day index tracker each day to see how it develops.
This year the trend for months to be milder than the Central England Temperature (CET) has continued. The values below from the TWO tracker show the recent anomalies against the often used 30 year series as well as the 1659-2020 one.
September: 13.6°C
August: 17°C
July: 16.4°C
June: 14.5°C
September shows a relatively weak positive anomaly, although the official CET for the month was 14.0°C, so a little higher than the TWO CET tracker. The absence of anomalous warmth persisting in September is considered to be a factor in favour of a colder winter when our final forecast is produced in late November.
At the moment most of the data strongly suggests a milder than average winter 2024-25. The exceptions are:
1) The possibility of a relatively weak SPV, at least early on
2) The wet and relatively cool September
Taking the above into account the initial TWO view is that the chance of a relatively mild season is higher than the norm. However, the risk of cold spells in late autumn and the first half of the winter is relatively high. The signal for precipitation is very weak, but on balance above average amounts of rain look more likely in the north than the south.
This feature will be updated through the rest of the autumn and the final forecast for winter 2024-25 will be published at the end of November.
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