Nitish Singh warned that thunderstorms in London and across Britain could begin on Monday, June 22, with model data pointing to the most violent thunderstorm conditions ever simulated. The risk may run through Friday, June 26, and the forecast points to lightning, hail, damaging winds, flash flooding and possible tornadoes.
Britain and the M4 corridor
The setup hinges on temperatures reaching the mid to high 30s Celsius, dew point values rising into the low to mid 20s, and CAPE running from 2,000 to 5,000, with one reading beyond 7,000. In Britain, a summer CAPE value of 1,000 is already notable, which is why this week’s numbers stand out.
Monday offers clear triggers, so widespread storms look likely, especially along the M4 corridor near Bristol, Swindon and Gloucester, and into North Wales. That leaves people in Britain with a short window before the most unstable air arrives.
CAPE and supercells
When winds change speed and direction with height, storms can begin to rotate. Rotating storms are known as supercells, and the forecast says that kind of structure is possible here.
The combination is unusual for Britain and is being described against a severe-weather setup that may last the full week rather than a single afternoon. That makes Monday the first day readers in the affected areas need to treat as the start of a run of hazardous weather, not an isolated storm burst.
June 26 forecast window
The most immediate focus is Monday, when the trigger environment looks strongest and the storm coverage is expected to be widest. Later in the week, the energy may linger even if the exact spark becomes less certain.
For readers along the affected corridor, the practical move is to plan for repeated thunderstorm disruption between June 22 and June 26, with the highest risk early in that stretch. Whether the forecasted extreme thunderstorm conditions will actually materialize over Britain as modeled is the question now hanging over the week.
