By Brian Gaze
After a long run of mild winters lasting through much of the 1990s and 2000s, a run of colder winters started in 2008-09 and finished in 2012-13. Since then they have been mainly mild, although 2020-21 was slightly colder than average across the UK as a whole.
Late February 2018 brought a spell of severe wintry weather dubbed the Beast from the East, but despite that the last notably cold month was March 2013 when the mean UK temperature was 2.2C, which is 3.3C below the average. Prior to that, December 2010 was the first calendar month since February 1986 to record a sub-zero Central England Temperature (CET).
The list below shows temperature anomalies in UK winters since 2008-09.
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.
Very mild. The third warmest in the series from 1910. The UK mean temperature was 5.5C, which is 1.8C above the average.
Very mild. The UK mean temperature was 5.0C, which is 1.3C above the average.
Close to average. The UK mean temperature was 3.6C, which is 0.2C below average.
Much milder than average. The UK mean temperature was 5.2C, which is 1.4C above average.
Much milder than average. The UK mean temperature was 5.3C, which is 1.5C above average.
Close to average. The UK mean temperature was 3.5C, which is 0.2C below average.
Milder than average. The UK mean temperature was 5.2C, which is 1.1C above average.
Last winter was milder than the average. Rainfall levels across the UK were 93% of the norm and sunshine levels were 101% of the average.
To summarise: Since 2010/11 there has not been a significantly colder than average winter. There were wintry spells in both 2012/13 and 2017/18 but most of the cold weather occurred in the meteorological spring and so does not impact the statistics presented here. Winter 2020/21 was slightly colder than the norm, but the anomalies were most significant in the north.
Grand Union Canal in Berkhamsted, March 2018
Last winter was mild and in the south there was very little snow. How are things shaping up this time?
Publicly available data from most of the seasonal models goes as far as the end of February 2022.
D/J/F = December, January, February
The Climate Forecast System v2 is available on TWO. View the latest CFS v2 charts.
Apart from the International Research Institute and ECCC all of the models listed are either showing no bias or above average temperatures. This is very similar to what the seasonal models were showing in September 2021.
In terms of precipitation there is currently a relatively weak signal for a wetter than average winter. However, long range forecast model skill levels for precipitation in the UK are very low.
To summarise: At the time of publication it would be reasonable to assume that most of the seasonal computer models are favouring a winter with a mostly positive North Atlantic Oscillation (NAO) pattern. Long periods of relatively mild, wet and windy conditions would be likely.
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 a neutral or negative NAO is considered to be higher than the norm during the early part of the winter. Towards the end a positive NAO is favoured.
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 QBO is currently in a positive westerly phase. The current expectation is for the QBO to remain in this state through the coming winter.
On balance the latest developments increase the likelihood of a milder and wetter than average winter.
El Nino takes place when SSTs in the central-east Pacific are anomalously warm and La Nina when they are colder than average. ENSO has an impact on global weather patterns, although the link to the UK is quite weak. A weak El Nino event is believed to increase the chance of colder weather during the second half of the winter.
Forecasting the ENSO conditions several months ahead is prone to error, but at the moment there is a 91% chance of a La Nina event persisting through to November and a 54% chance of it continuing through to March 2023.
The TWO view is a weak La Nina increases the chance of a cold winter in western Europe. A strong event probably diminishes it. However, in general terms a La Nina is believed most likely to increase the chance of cold snaps during the early part of the winter.
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. Levels of solar activity through 2022 have been higher than some predictions.
The higher levels of solar activity may increase the chance of a mild winter in western Europe.
This year for the first time we are running an automated system which 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 30th September, 2022, the 5 closest matches over the last 30 days are:
2010-11 was cold overall, but largely because of the extreme December. January and February saw mid conditions becoming established
1998-99 was a mild winter
2004-05 was a mild winter
2007-08 was a mild winter
2001-02 was a mild winter
Therefore, the analogue index at the time of publication is favouring a milder than average winter.
You can view the latest 30 day index tracker each day to see how it develops.
At the moment most of the data is suggesting a milder than average winter 2022-23.
The seasonal models strongly support the idea of it being milder than average. The precipitation signal is much weaker. The QBO also suggests a lower chance of a cold winter. High levels of solar activity this year may also favour a mild winter.
The La Nina phase is forecast to continue. It is a factor which may increase the likelihood of a cold weather during the first half of the winter. The relatively early state of solar cycle 25 could also suggest an increased chance of a colder winter. Nonetheless, both of these factors are tenuous at best.
The analogue index top five has four members which had milder than average winters.
Recent climatology again favours average to milder conditions. This year there hasn't been a colder than average month so far.
Taking the above into account the initial TWO view is that the chance of a relatively mild season is higher than the norm.
Regular updates will be issued before the TWO winter forecast is released at the end of November.
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