Nocturnal 
The warm spell is over. After a run of temperatures as high as 28C, cooler air is moving in across the UK this week, with daytime highs set to fall closer to – or even below – the seasonal average, according to the BBC.
It’s a sharp change of pace after what’s been a mild start to autumn. The BBC reports that by Wednesday, afternoon temperatures are expected to range from just 11C in northern Scotland up to 17C in southern England. If no part of the UK hits 20C this week, it’ll be the first time that’s happened in months – a sign of just how warm things have been running until now.
The term “polar vortex weather” has also been trending in UK search results, with more than 50,000 people searching for it, as the public reacts to the sudden shift from shorts-and-t-shirt conditions to coats-and-brollies weather.
Why it matters
The cooldown isn’t just a one-day blip – it’s being driven by a weather front moving erratically southwards through Monday, Tuesday and Wednesday, the BBC says. That front will bring outbreaks of rain, heaviest in the north and west and lighter further east, with the possibility of thunder and lightning reaching southern and south-eastern England on Tuesday night and into Wednesday.
Scotland looks set to bear the brunt of it, with heavy rain expected in the west and gusts of 40mph or more forecast for the far north-west. Northern Ireland will see cloudier skies with light rain and drizzle, while some mist and fog could linger in parts of south Wales, the Midlands, East Anglia and southern England before the change properly kicks in.
Once the rain clears south, cooler air will follow in its wake. The BBC forecasts some chilly nights by midweek, with a touch of frost possible in parts of the country that are prone to it – a proper reminder that autumn has arrived.
Separately, forecasters at yourweather.co.uk have pointed to northerly winds as the trigger for the sharper chill, after temperatures climbed as high as 23C for some areas just days earlier.
What happens next
Despite the cooler, wetter week ahead, it isn’t all bad news for anyone still hoping for a bit more warmth. Met Office figures show this autumn has so far been running warmer than usual, with September ranking as the joint-fourth warmest on record for the UK, at 1.6C above the long-term average.
Longer-range forecasts suggest the season as a whole is still likely to finish warmer and wetter than normal, with the chance of stormy weather later on – partly linked to a developing El Niño pattern in the Pacific, according to the BBC. The UK remains on track to record one of its warmest years overall.
For now, though, the message is simple: pack an umbrella, dig out a jumper, and don’t expect those late-September highs to stick around. Readers are advised to check local forecasts regularly, as the exact timing of rain and temperature drops will vary by region through the week.
