Met Office yellow warning: thunderstorms to break the May heatwave tonight

The Met Office has issued a yellow-level thunderstorm warning lasting from 3pm to midnight tonight (Wednesday 28 May 2026), covering large parts of Wales and south-west England. The warning marks a sharp, unstable end to the record-breaking May heatwave that pushed temperatures to 35.1°C at Kew Gardens earlier this week.

What's covered

The yellow warning zone centres on Wales and the South West, with the threat extending into parts of Hampshire and the West Midlands — specifically Herefordshire, Shropshire and Worcestershire. Elsewhere in England and Scotland conditions will remain warm and largely dry through the evening, though further outbreaks of heavy rain are possible overnight.

What to expect where storms develop

The Met Office warns of:

• Torrential downpours — up to 30–40 mm possible in a short time where the heaviest cells train
• Frequent lightning and loud thunder
• Large hail — stones greater than 20 mm are possible in the most intense cells
• Strong, gusty winds — locally damaging gusts in and around storm cores
• Flash flooding of roads, underpasses and low-lying properties
• Delays to road, rail and public transport services
• Possible lightning strikes causing short-term power outages

Why tonight

The record heat of the last few days has loaded the lower atmosphere with exceptional moisture and instability. A shortwave trough approaching from the west is the trigger — storm development is expected to be slow to initiate but rapid once under way, with organised multicell clusters or isolated supercells possible across the warning zone during the mid to late afternoon and evening.

This is a classic heatwave-break setup. The contrast between the residual 30°C+ surface temperatures and cold mid-level air spilling in behind the trough creates the steep lapse rates that fuel explosive storm growth.

Stay safe

If you're caught outside when thunder is audible, seek a hard-topped vehicle or a substantial building immediately. Avoid open fields, hilltops, lone trees and large water bodies. Do not shelter under isolated trees — a direct strike to a tree can conduct through roots and across wet ground for several metres.

For real-time strike data, lightning alerts and storm reports from the community, stay on ChaseitUK.

Met Office yellow warning active 28 May 2026, 1500–0000 BST.