Why summer heat is unlikely to return to the UK anytime soon

First spell of summer heat

Finally, the UK had its first notable spell of summer heat earlier this week. The temperature reached 30.5C in Wisley, Surrey on Wednesday, making it the warmest day of the year so far. Elsewhere, parts of Scotland and Wales reached the high 20s, and Northern Ireland the mid 20s. Whilst this sort of heat in June isn’t unusual, it follows a cool start to the month where mean temperatures have been 1-3C below average.

With the heat swept away, temperatures have now tumbled back down to average for many. The return to cooler weather has also seen some unseasonably windy conditions for parts of Scotland and Northern Ireland, accompanied by showers or longer spells of rain.

No signs of heat returning soon

If you’re wondering when the next spell of summer heat is coming, the short answer is not anytime soon. The ECWMF weather model (below) shows that for next week, the first week of July, mean temperatures are expected to be 1-3C below average for almost all of the UK. The cool anomaly will be most marked across northern and western areas, due to cool, fresh winds blowing off the Atlantic Ocean.

Active jet stream

The reason summer heat is unlikely to return anytime soon, is that the jet stream (yellow/orange/red below) is forecast to be unseasonably active over the Atlantic Ocean for the coming 10 days.

This will bring a changeable flavour to our weather patterns – more akin to early autumn. Whilst there will be some ridges of high pressure bringing drier, brighter and slightly warmer days, there’ll also be areas of low pressure bringing brisk winds, spells of rain and a cooler feel – especially in the west.

Uncertainty further ahead

It’s worth emphasising that summer is a notoriously tricky time to predict the weather far in advance. Changes in the jet stream and weather patterns can happen much more slowly at this time of year. This significantly reduces predictability beyond a few weeks at most.

The other element of jeopardy as we move into July is that tropical storm activity over the Atlantic Ocean is starting to increase. Today’s forecast from the National Hurricane Center suggests that there’s a 90% chance of a tropical disturbance eventually becoming a named storm within the next week.

Why does this matter? Well, if these disturbances grow into powerful hurricanes, they can significantly influence the position of the jet stream, which in turn can affect our weather down the line.