UK summer weather forecast

Summer 2024 was the coolest since 2015 across the UK as a whole. The mean temperature was 14.37°C, which is 0.22°C below the 1991-2020 average. Rainfall was 95% of the 1991-2020 average and sunshine was 97%. Despite this, perceptions of the season were quite mixed, with the second half bringing warmer conditions. It is also worth noting that much of England and Wales experienced drier than average conditions, and temperatures were very close to the norm. Will summer 2025 follow a similar pattern?

Autumn was slightly milder than average, with mean temperatures of 9.92°C which is 0.20°C above the 1991-2020 average. Rainfall amounts were slightly below average, but there were significant regional variations.

Despite several colder periods the winter as a whole was milder than average. The mean temperature was 4.62°C which is 0.53°C above the norm. Rainfall and sunshine amounts were also slightly below average.

March has been a very dry month. In fact England and Wales experienced their driest March in over 60 years. In the short term the dry conditions are expected to continue.

Dry weather continued through much of April and temperatures were well the long term average. Current guidance suggests May will bring a lot of settled weather as high pressure continues to dominate.

What period is summer?

To be clear, the period under discussion here is the meteorological summer. It runs from 1st June to 31st August. The astronomical summer in the Northern Hemisphere begins on 21st June and ends on 22nd or 23rd September.

Because the meteorological seasons cover fixed months they make it easier to consistently compare data across years and decades. In the digital age that is less of an issue than it was, but records span hundreds of years, many of which predate modern computers.

How is the long range forecast made?

When looking at long term weather prospects, a number of inputs can be considered. These include seasonal models and analogues, which compare recent weather patterns with those of past years.

Teleconnections which describe how persistent weather patterns in one part of the world can influence weather patterns in another, are also considered in The Weather Outlook seasonal forecasts. However, their links to the UK's weather are generally weak, particularly in the summer. Nonetheless, in this discussion, the ENSO outlook is referenced. North Atlantic Sea Surface Temperatures (SSTs) are also included.

Seasonal models

Seasonal models are run by a number of national forecasting systems. They provide indications of global trends for the coming months, but their skill level (accuracy) for the UK remains low. Nonetheless they are a good starting point when considering future prospects.

The Copernicus Climate Change Service (C3S) runs a multi model ensemble, which combines data from a number of models, including the UK Met Office GloSea, Météo-France, DWD (Germany) and CMCC. It provides probabilities for different scenarios, e.g., warmer or colder, wetter or drier than average.

Unlike short and medium range models which update several times each day, refreshes to the seasonal models tend to be monthly.

So what do they indicate at the time of publication? 

Temperature trends

The C3S strongly favours above average temperatures, as can be seen on the chart below. Of note is that virtually the whole of Europe is in the "very high" confidence band indicating that temperatures will be in the upper tercile, which represents the warmest 33% of historical data.

Note: Since the first update the temperature signal has not changed significantly. Therefore, the chart above has not been updated.

Usually the signal for temperatures is stronger than it is for rainfall. Rainfall amounts can often vary significantly as a result of small changes in the position of the jet stream. Modelling these months ahead is not currently possible. Also, in the summer months convection plays a big part, leading to the development of showers and thunderstorms. They can drop large amounts of rain in very localised areas. But does the C3S give any indications on whether it will be a drier or wetter season? 

Rain trends

The chart below is similar to the one above, but instead of temperature probabilities it shows precipitation probabilities. The suggestion is that the north west of the UK is more likely to have a wetter than average season than a drier one. Note: This signal was not as clearly defined on earlier updates. In fact, drier than average conditions were previously favoured in parts of the UK.

Although the confidence level is low, falling into the 40-50% range, it is still significant. Why? A key reason is that it is generated by averaging out the forecasts from a number of seasonal models, as previously discussed. Therefore, if a signal is still present it suggests underlying factors are broadly supportive. The second reason is the yellow shading which indicates this covers most of Europe, rather than just a small section of it.

ENSO forecast indicates change

The state of the El Niño Southern Oscillation (ENSO) has significant impact on temperature and rainfall patterns around the globe, but its link to the UK summer is weak.

Latest forecasts suggest a greater than 50% chance of ENSO-neutral conditions continuing through the Northern Hemisphere summer and well into the autumn.

The ENSO outlook doesn't favour a particular outcome. 

An active hurricane season?

Forecasts are suggesting a more active hurricane season than normal. Would that lead to a washout summer in the UK? Not necessarily. It's possible that ex-hurricanes in the North Atlantic could increase the chances of blocking areas of high pressure developing over Europe.

The warmer than average Sea Surface Temperatures (SSTs) in much of the Atlantic also support the idea of higher than normal temperatures in the UK.

High temperatures in recent summers

In recent decades periods of extreme heat have become more frequent in the UK. Summer 1976 is often used as a benchmark because the dry and hot weather persisted for such a long time. However, the highest temperature recorded then, 35.9°C in Cheltenham on 3rd July, has been easily surpassed a number of times in recent years. In 2022 it was beaten by a huge 4.4°C in 2022, when 40°C was exceeded for the first time on record in the UK. 

Maximum temperatures for recent years are listed below:

2024: 34.8°C, 12th August, Cambridge

2023: 33.2°C, 9th September, Kew Gardens

2022: 40.3°C, 19th July, Coningsby, Lincolnshire

2021: 32.2°C, 21st July, Heathrow, Middlesex

2020: 37.8°C, 31st July, Heathrow, Middlesex

2019: 38.7°C, 25th July, Cambridge Botanical Gardens

2018: 35.3°C, 26th July, Faversham, Kent

2017: 34.5°C, 21st June, Heathrow, Middlesex

2016: 34.4°C, 13th September, Gravesend, Kent (Note: This was in the meteorological autumn)

2015: 36.7°C, 1st July, Heathrow, Middlesex

The last time 30°C wasn't reached in the UK was in 1993. In that year the top temperature recorded was 29.7°C in East Bergholt, Suffolk. In more recent times, 2007 and 2008 brought maximums of 30.1°C and 30.2°C respectively.

Recent climatology

The trend in recent months continues to favour above average temperatures, although the Central England Temperature (CET) for January was 0.4°C below the 1961-90 average.

Weather analogues

This involves comparing historical weather patterns with current ones. On The Weather Outlook (TWO) the  Weather Analogue Index (WAI) is updated every day. It compares current weather patterns in the Northern Hemisphere with those at the same time in every year going back to 1948.

To reduce variability, an average is built over extended periods, for example 30 days. At the time of publication the top 10 best matches for the 30 day tracker are shown in the table below. 

The first update published in March showed a very mixed picture. The analogues have now shifted towards favouring a cool and probably quite wet summer. Of the 10 best matches, 6 were cooler than the 1961–90 average. If that were to occur this year it would be quite a shock, particularly given how few months have fallen into this category in recent years.

Summer now looking more mixed?

1) Seasonal models strongly forecast above average temperatures over the June, July and August period

2) Since the previous update a signal for a wetter than average season in the north west has emerged from the seasonal models 

3) ENSO neutral conditions are expected

4) Early forecasts for the 2025 Atlantic Hurricane season a more active hurricane season than average

5) Recent climatology favours warm weather

6) Northern hemisphere analogues favour a distinctly cool summer 

Therefore, at this stage it is the analogues versus computer models and recent climatology.

The summer forecast will be issued at the end of May.