Convective Outlook UPDATED: High risk 21/06/2025 06:00 - 22/06/2025 05:59

UPDATE (21/06/2025 12:10): The high risk has been expanded based on the latest observation. A supercell is likely to form across NE Wales into Manchester. Large hail and tornadoes are possible.

An outbreak of severe thunderstorms and supercells is likely across parts of Wales and Northern England during the late afternoon into early evening. Today's setup is rather rare and severe due to the overlapping of very favourable ingredients and unusually strong cross-model agreements.

A plume of warm theta E plume across most of England and Wales should support severe thunderstorms to form today. As an arm of strong directional shear across the eastern quadrant of a low-pressure system interacts with the theta-e plume, thunderstorms are likely to initiate across Wales and NW England, spreading northward into northeast England and southern (perhaps even eastern) Scotland as well. A warm nose at 850 hPa will serve as an atmospheric cap, preventing any lift of air parcels high up in the air, strongly limiting any showers from developing into thunderstorms. Once the convective temperature of around 27-28 °C is exceeded in Wales, strong and severe surface-based thunderstorms will start to develop locally, turning increasingly widespread very soon after initiation due to sea breeze convergence, sufficient shearing (35-45 kt) and CAPE (1200-1700 J/kg). These thunderstorms will have very high cloud tops (37000- 39000 ft), favouring frequent or even very frequent lightning strikes. A good mid-level lapse rate, strong updraft, and sufficient CAPE will also support the formation of large hail with a diameter of 2-3 cm, perhaps 4 cm max. All these background environments are pointing to an elevated risk of supercells, as well as tornado activity before the storms turn elevated during early night. Therefore, a large HIGH risk has been issued due to the severity, widespread and confidence of today's event

After the initiating phase, thunderstorms will turn increasingly elevated, reducing the tornado risk while increasing the chance of strong gusts of up to 60 mph due to the increasing strength of theta-W in the northeast. Strong PWAT (40-45mm) supports an elevated risk of flooding, perhaps even severe flooding locally due to the training effect.

A conditional risk of further thunderstorms is possible across the East Midlands and East Anglia overnight, but it is rather unlikely due to the CAP preventing air parcels from rising.

Again, such a severe event is rather unusual in the UK, and this is likely to be the strongest outbreak of thunderstorms since 2022.

You can download the kml file of the convective outlook here:

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