What happened to summer 2024?
by Kirsty McCabe, FRMetS
Summer 2024 has not won many fans (aside from slugs and snails). Cool, cloudy and wet aren’t ideal conditions for barbecues, summer festivals or sporting events, but are we being unrealistic? How terrible has it been, is it normal and will it ever improve?
The big player in determining what weather we get is the jet stream. This fast-moving ribbon of air high in our atmosphere steers low pressure systems around. If the jet stream is over us, you can expect wet and windy weather to head our way. Usually in the summer the jet stream moves to the north of the British Isles, and this allows warmer air to move in from the south, especially if a ridge of high pressure extends from the Azores, aka The Azores High. If high pressure sits over the UK for a prolonged spell of time, temperatures will rise in the sunny skies, and then of course we’ll start complaining about heat, drought and wildfires. But so far in 2024 we’ve not had to worry about that.
Instead the first half of summer 2024 has seen the jet stream sitting across and even to the south of the UK, and that has meant spells of wind and rain interspersed with some brighter interludes. But even then it hasn’t felt like “summer” because we’ve been in quite a chilly airmass with cool northerly winds. Cool enough that we’ve been digging out our jumpers and tempted to turn the heating back on.
Mean temperatures for June 2024 averaged out at just 0.4°C below the norm. But that’s thanks to one short blast of hot weather at the end of the month masking the previous three weeks of chilly conditions in brisk Arctic winds. It then went cold again for the start of July 2024, with mean temperatures running 2.4°C below average under cloudy skies. All of which is a big contrast to the previous year, when June 2023 was the hottest June on record for the UK.
In terms of rainfall, June 2024 was actually quite dry, with only northern Scotland exceeding its average rainfall. So you could say the repeated wet spells during the first half of July 2024 are actually welcome news for our gardens, with parts of southern England receiving a month’s worth of rain in a week. But it's not great timing for more traditional summer activities.
Great British Summer
Glastonbury Festival is known for its mud baths and Wimbledon installed roofs over its main tennis courts at SW19, so it’s not unusual to get rain at this time of year. What’s more unusual is how persistent the unsummery weather has been, with summer 2024 certainly one of the coldest in recent years.
What would we normally expect in summer? Looking at the average summer temperatures over the past 30 years, you would expect daytime highs to reach the mid to high teens in Scotland, and the high teens to low twenties further south, with the highest temperatures focused around London, southeast England and East Anglia. That's obviously an average so you would expect temperatures to be higher and lower at different points through the season, but it's a useful reference point.
And if we look at the previous 30-year-reference periods (below), you can see that average summer temperatures have been gradually rising with more dark reds in the southeast. Which makes 2024’s cooler spell even more noticeable.
But summer is a game of two halves, and the rest of July and August 2024 could bring warmer and drier weather that balances out the cool and wet conditions so far — just as that short blast of heat in June masked the chilly air that most of us remember. In fact, it does look like things are set to change with model forecasts leaning towards high pressure building from mid July. And don’t rule out a hot spell in September either, as that seems to have become the new normal in recent years.
What happened to climate change?
For those who might think a cool summer in the UK means global warming isn’t happening, think again. Northwest Europe may have been cool and wet, but that’s not been the case elsewhere. Central and southeastern parts of Europe have had early summer heatwaves with temperatures into the mid-40s in places. Extreme heat has also affected North America, with Las Vegas recording its highest temperature on record with 49°C (120°F) on 7 July 2024.
We will still have cooler years in the future, but not as many of them. The global picture clearly shows a worrying long-term trend of rising temperatures and a warming climate. June 2024 was warmer globally than any previous June in the data record. And it was the thirteenth month in a row that is the warmest for the respective month of the year.
