Summer 2024: Seasonal models suggest a very warm one, but rainfall signal uncertain

Rest of May

The first half of May is shaping up to be significantly warmer than average, up to yesterday, 2C warmer than average for the UK, while rainfall is running near average. The long-running Central England Temperature (CET) is running 3C above the 1961-1990 long term average. We’ve seen temperatures reach 27C over the weekend, but it’s likely the warm nights that have also kept the running mean temperature well-above average.

The rest of the month the signal is looking more uncertain. Low pressure looks to linger towards the south through into early next week, so changeable conditions likely in the south, with showers or longer spells of rain at times but also some drier sunnier weather, while higher pressure towards the north will bring drier and more settled conditions here. Confidence lowers from the middle of next week, but it looks most likely pressure will rise across most areas for a time, bringing more settled conditions for all. But from the weekend of 25th/26th, pressure looks to drop from the west, with a resumption of unsettled conditions. However, generally it looks like temperatures will remain around or slightly above average for the rest of the month.

All of the last 4 months have been above average temperature-wise and it looks likely May will follow suit.

A look at summer using the May updates of the seasonal models

With summer just around the corner, I’ve been looking at what might be in store. Last week I did a blog looking at what the coming summer may have in store weather-wise. I discussed the various drivers that can shape the season, such as ENSO and Atlantic sea surface temperatures, but also we had a brief look at what the Numerical Weather Prediction (NWP) models were showing. Last week, it was only the European ECMWF model that had updated for May. But since then, other models have been updated for My on the Copernicus C3S Seasonal Charts page.

June

For June, it’s a mixed picture from the models, but what most stands out is that ECMWF looks on its own with a signal for high pressure covering northern Europe, including the UK, while other main models (UKMO, NCEP & Meteo France) are showing low pressure over NW Europe. The latest update of the long-range EC46 run of ECMWF, which looks 46 days ahead, goes against the seasonal outlook too and suggests high pressure to the south and lower pressure to the north – indicating a westerly or southwesterly flow.

The ECMWF seasonal update suggests an average to slightly drier signal from its precipitation forecast, while the other models are average to slightly wetter than normal signal, thanks to low pressure nearby. Meteo France looking the ‘wettest’ across the whole of the UK followed by UKMO.

With regards to temperatures, general picture across the model output for June is for temperatures to be above average, 0.5-1C above. NCEP the warmest of the bunch. Generally, the picture is unsettled at times, with rain for most, but warm.

July

A look at July, again ECMWF looks more on it’s own, with signal for lower pressure over northern and eastern Europe, while UKMO, NCEP and Meteo France have lower pressure towards Iceland and southern Europe, average or slightly higher pressure tendency in between.

All models showing temperatures above average, NCEP warmest, with 1-2C above average. Rainfall signal more mixed, but no particularly dry signal from any of them. No signal to slightly above.

August

The cross-model signal for August looks similar to July, lower pressure towards Iceland and southern Europe, no signal in between. But individually some differences,  ECMWF and UKMO have a stronger signal for lower pressure to the north and northwest. NCEP a strong signal for lower pressure to the west.

All models look warmer than average for August, generally 0.5-1C. Precipitation signal looks more mixed, but generally no signal for wetter or drier.

Summary of the seasonal model output

In summary, for all three summer months, there is a unanimous signal from all models for above average temperatures in most of the UK over June, July and August. The rainfall signal is more mixed and less clear, with generally no signal for wetter or drier, so on balance, average across all three months.

The full summer forecast will be issued towards the end of the month and will look in detail at the drivers that could shape the weather patterns through the summer, as well as reference to the seasonal model output discussed above.