Atlantic rain is set to end the quieter spell and bring wet weather across much of the UK on Thursday, with showers on Wednesday giving way to a more organised band of rain and thunderstorms. The heaviest rain is expected in Wales, southwest Britain and then later across Scotland as the system moves through.
The change matters now because Thursday is the day the weather pattern shifts. Eastern Britain and Shetland began Wednesday with sunshine, but showers were already building elsewhere and heavier downpours were expected later in eastern counties as they eased farther west. Temperatures were around 14C to 17C, but the forecast is moving from short-lived showers to a much broader wet spell, which is why the met office rain list is being watched so closely.
A dominating Atlantic low pressure system will slide north of Scotland, from Iceland to Sweden, and that will hamper high pressure trying to build over southern Britain. A cooler flow around the low will feed down the North Sea, while high cloud from the Atlantic is expected to bring wet weather across the UK on Thursday. Heavy showers are expected to develop widely through the morning inland, with thunderstorms also possible as surface heating steepens low to mid-level lapse rates. The strongest instability is expected toward eastern England and eastern Scotland in the afternoon.
Wales is expected to see a wet Thursday, with heavy rain over the mountains and western counties. Blustery wet conditions are also expected around the Irish Sea and across southwest Britain on Thursday morning, while southeastern Britain is due to turn wet by lunchtime. First thing on Thursday, the frontal rain is not expected to have reached northern Scotland or Norfolk and Suffolk, but the main rainband is forecast to move from northwest England and western Scotland across more of Scotland into Thursday evening.
There is still the potential for temperatures to climb into the high twenties Celsius and even pass 30C later in the period, but confidence in that warm weekend signal has lowered. The weekend heat is not gone, only less certain, and the rain arriving on Thursday is the reason the forecast has become harder to pin down. The rain is expected to ease from Northern Ireland and southwest England during the day, and the winds will veer from southerly to westerly as the system passes through.
For readers looking ahead, Thursday is now the key day: rain spreads in, thunderstorms may flare, and the strongest wet weather is likely to focus on Wales, southwest Britain and then Scotland before the band clears eastward.
