The weekend is looking generally cloudy, but warm and muggy, thanks to a long-fetch warm and moist southwesterly flow sourced from the sub-tropical Atlantic. The cloud will be thick enough across northern and western parts on Saturday to bring patchy rain, particularly over higher ground. On Sunday, fresher and brighter conditions will push down across northern and perhaps central parts eventually behind a cold front sinking southeast. But southern England likely hanging on to cloud, muggy and very warm conditions where, despite the cloud, we could hit 26C.
Then on Monday, high pressure builds in across the UK from the southwest, so many should be fine, dry and sunny. Still warm, muggy and perhaps rather cloudy across southern England close to a slow-moving but weak frontal boundary, the same front that slipped southeast on Sunday.
Tuesday & Wednesday see increasing risk of storms and brief heat
Then from Tuesday the weather turns interesting … if you like thunderstorms, heat and humidity. An area of low pressure moves north over Biscay and western France, drawing hot and humid air north across France which will be conditionally very unstable. The large amounts of convective energy (CAPE or convectively available potential energy in meteorology) looks to be released in the form of thunderstorms as the low and upper trough moving in from the west interacts with this plume across northern France and eventually southern England on Tuesday and into Wednesday. Though details and timing this far out are far from certain for now.
Temperatures could climb into the mid-20s on Tuesday afternoon across southern counties of England, but the plume of warm and humid air arrives from the south behind a warm front Tuesday night, accompanied by some thunderstorms drifting into southern England. The plume from France briefly surging north across central, southern and eastern England on Wednesday behind early morning storms spreading north – with afternoon temperatures peaking in the high 20s across SE England and East Anglia where sun comes out, perhaps a few spots 30C. However, a trough of low pressure and surface cold front moving across the UK from the west will likely trigger further storms as it begins push out the hot and humid air.
This loop of weather type charts, based on GFS, show storms developing and spreading NE from Tuesday evening through Wednesday. Red symbol = thunderstorm. Credit: wetter3,de.
Cooler end to the week
Then a much cooler and fresher end to the week, as winds switch to a westerly direction behind the trough moving through, with temperatures back down into the low 20s in the SE and mid-to-high teens elsewhere.