London Weather Outlook Points to 21C Before Cooler Air Returns

London weather could reach 20 or 21C on Saturday as warm air holds across southern England at the start of the weekend. A frontal boundary will then slide south through Britain, bringing cooler air, showers and a frost risk to southern England by Sunday night.

Saturday Weather Over London

The warmest air will sit in the south, where temperatures could range from 16 to 20C and even nudge into the low twenties on Saturday. Further north, values are expected to stay around 10 to 15C, showing the sharp split across the UK.

That divide is set by a frontal boundary separating warmer continental air to the south from colder Arctic air. As the weekend starts, England and Wales are expected to have warm air and light winds, which gives London the best chance of reaching the higher end of the forecast.

Essex Boundary By Sunday

The boundary is expected to slowly sink southwards over Britain and clear from Essex by Sunday lunchtime. Before then, Saturday morning could bring a damp zone stretching from Fife across southeast Scotland and northeast England to the Humber.

Showers are also in the forecast, with the potential for thunderstorms on Saturday afternoon. By Saturday evening, there could still be a scattering of heavy showers, although plenty of bright or sunny spells are still expected.

Cooler Air Over Southern England

A brisk northeasterly wind is expected to pick up in northeastern England and add to the grim feel of the day. By Sunday, a new low pressure system is expected to develop south of Iceland and move towards Scotland, helping pull a cooler flow right down through the UK.

That cooler air is expected to reach southern England by Sunday night, when frost becomes a risk. More chilly air is expected at the start of next week, ending the short warm spell that London could see on Saturday.