16th September 2023
By Brian Gaze
The list below shows temperature anomalies in UK winters since 2008-09. It is worth noting there hasn't been a significantly colder than average winter since 2010-11. Although 2012-13 and 2017-18 brought significant wintry periods, most of the cold weather occurred in the meteorological spring which starts on 1st March.
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 5.5°C, which is 1.8°C above the average.
Very mild. The UK mean temperature was 5.0°C, which is 1.3C above the average.
Close to average. The UK mean temperature was 3.6°C, which is 0.2°C below average.
Much milder than average. The UK mean temperature was 5.2°C, which is 1.4°C above average.
Much milder than average. The UK mean temperature was 5.3°C, which is 1.5°C above average.
Close to average. The UK mean temperature was 3.5°C, which is 0.2°C below average.
Milder than average. The UK mean temperature was 5.2°C, which is 1.1°C above average.
Close to average. The UK mean temperature was 4.3°C, which is 0.2°C above average.
The overall mean temperature for last winter was very close to the average. However, that masked large variations, with December bringing a significant cold spell which brought snow to parts of the UK. The season was drier than the average, with rainfall levels across the UK at 81% of the norm. It was also sunnier than the 1991-2020 average, with 113% of sunshine hours.
Does the run of relatively mild winters mean "we are due a cold winter"? Not necessarily. If anything, it could be argued that the run of mild winters means the odds are currently stacked against colder scenarios. Forcing mechanisms, background levels of warmth and persistence may continue to promote milder outcomes. In the UK, there is a tendency for cold winters to come in clusters, but identifying when one is likely to start is very difficult.
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.
Publicly available data from most of the seasonal models goes as far as the end of February 2024.
D/J/F = December, January, February
The Climate Forecast System v2 is available on TWO. View the latest CFS v2 charts.
Above average temperatures and precipitation levels are being suggested. The accuracy of seasonal models is still low for the UK, but with that said, they are unusually consistent with each other at the present time. In particular, the signal for precipitation is more consistent and stronger than is often the case.
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. Higher than normal levels of rainfall would suggest a vigorous Atlantic flow for long periods.
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 increase during the second half of the winter. However, if the pattern becomes based further west it can actually lead to mild conditions in the UK.
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 negative phase during the coming winter.
On balance this increases the likelihood of a colder and drier than average winter because there is a correlation between a negative QBO and a weaker jet stream.
El Niño 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.
Forecasting the ENSO conditions several months ahead is prone to error, but at the moment there is a 95% chance of the current El Niño phase persisting through to March 2024.
A weak El Niño event is believed to increase the chance of colder weather during the second half of the winter. Conversely, a strong event may be linked to milder and wetter than average winters in western Europe.
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 in 2024.
The high levels of solar activity which are expected, 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 16th September, 2023, the 5 closest matches over the last 30 days are:
Winter 2011-12 was milder than average
Winter 2004-05 was milder than average
Winter 2013-14 was milder than average
Winter 2012-13 was slightly colder than average
Winter 1969-70 was colder than average
Therefore, the analogue index at the time of publication is favouring a milder than average winter. It is also notable that four of the best matches have occurred this century.
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 2023-24.
The seasonal models strongly support the idea of it being milder and wetter than average. In fact, the signal for above average levels of precipitation is unusually strong.
The negative QBO suggests a higher chance of a cold winter.
High levels of solar activity as the next peak approaches may favour a mild winter.
The El Niño phase is forecast to continue. It is a factor which may increase the likelihood of a mild and wet start, with colder conditions becoming more likely during the second half of the winter.
The Weather Analogue Index favours a milder than average winter.
Recent climatology favours average to milder conditions.
Taking the above into account the initial TWO view is that the chance of a relatively mild and wet season is higher than the norm. There is thought to be an increased possibility of it being a very wet season.
Regular updates will be issued before the TWO winter forecast is released at the end of November.
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Models include UK Met Office UKV and MOGREPS-G, ECMWF, NCEP GFS, Meteo France Arpege and Arome.