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In this week’s Met Office Deep Dive, we unpack a weekend of dramatic weather across the UK, explore the science behind supercell thunderstorms, and look ahead to a week of changeable conditions shaped by a dynamic jet stream.

Was there a Supercell over the weekend?

So, did the UK experience a supercell thunderstorm? The answer, in fact, is yes, at least one storm bore the hallmarks of a supercell, and possibly more.

Supercells are the most organised and long-lived type of thunderstorm. They are defined by a rotating updraft, known as a mesocyclone, which allows them to sustain themselves for hours and produce severe weather including large hail, damaging winds, and even tornadoes.

While the UK rarely sees supercells, the ingredients were in place: strong wind shear, elevated instability, and a moist, warm air mass. Doppler radar showing rotation aloft, and hail reports of up to 2 cm in southeast Scotland, support the supercell diagnosis. One storm even showed potential for 4 cm hail, though this remains unverified due to its rural location and the fact that it occurred late at night.

READ MORE: What's in store for the next week: An active jet stream fuels more changeable weather

A finely balanced setup

The weekend’s weather was a case study in how delicate the balance can be between a major outbreak of severe weather and a more modest event. Forecast models had flagged the potential for significant thunderstorms, particularly across northern England and southern Scotland, but the outcome hinged on surface temperatures.

Early cloud cover and elevated convection, storms forming above a stable surface layer, limited daytime heating in some areas. While Surrey saw temperatures in the low 30s, parts of northwest England and northeast Wales remained cooler than expected, reducing the likelihood of surface-based storms.

Two scenarios were considered: one where surface temperatures rose enough to trigger deep convection and potentially tornado-producing supercells, and another where elevated storms dominated. The latter played out, but not without impact. Multiple storm cells tracked over the same areas, bringing over 40 mm of rain and some localised flooding.

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