Weatherwatch: Why Britain’s heatwaves don’t always end with thunderstorms

Temperatures in the city climbed to a record 38C in June. Photograph: David Burton/Alamy View image in fullscreen Norwich Cathedral at sunset. Temperatures in the city climbed to a record 38C in June. Photograph: David Burton/Alamy Weatherwatch: Why Britain’s heatwaves don’t always end with thunderstorms The science behind summer storms – and why they have yet to break the hot spell gripping the country “The English summer: three fine days and a thunderstorm,” George II is reputed to have said, although the line has also been attributed to Charles II and others. It was not recorded until 1867, . A brief hot spell ending in a thunderstorm is a familiar pattern, but it is not what we have experienced in recent weeks. Summer thunderstorms develop in an unstable atmosphere, where hot air warmed by Earth’s surface sits beneath a layer of cooler air. Just a few days of sunshine can be enough to make warm, humid air rise, condense and build into towering cumulonimbus clouds. These are classic storm clouds, with rising and falling particles rubbing against one another, generating electrical charge. The resulting potential difference creates lighting. In some tropical regions, an evening downpour after a day of intense sunshine is almost routine. Hot weather alone, however, does not create instability. Sometimes there is little distinction between warmer and cooler air, with hot air leaking upwards at a steady rate without forming clouds. During a prolonged dry spell, limited evaporation at ground level leaves the rising air too dry to form clouds as it cools. Without that moisture, thunderstorms fail to develop – and the heatwave persists. Explore more on these topicsUK weather Weatherwatch Summer features Share Reuse this content Most viewed Most viewed