Severe Weather Forecast
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Convective Discussion +
00:50 BST Sun 16 May 2021 – 22:00 BST Sun 16 May 2021

Areas affected

  • The RoI
  • Northern Ireland
  • England
  • Wales
  • Southern Scotland
  • IoM


  • Isolated brief tornadoes
  • Gusty winds to 50mph
  • CG lightning
  • Hail to 15mm diameter


A large upper low will cross the Republic of Ireland and the UK through tonight and Sunday. At the surface, a low will move east across southern parts of the RoI and the southern UK through the same period. Through the remainder of the night, showers and perhaps an isolated thunderstorm will be mainly limited to the proximity of the upper low, namely the southern RoI and SW'ern parts of the UK. Gusty winds, and perhaps and isolated, weak tornado will be possible in these areas.

Through the daylight hours on Sunday, diurnal heating will lead to several hundred J/Kg of CAPE widely across the discussion area, and showers/thunderstorms will become rather numerous. Across southern parts of Wales and southern England/the south Midlands, backed flow ahead of the surface low may contribute enough low-level vorticity for one or two brief/weak tornadoes to develop - and deep-layer shear may be enough for a few organised storms/clusters to develop, with gusty winds/hail to 15mm diamater.

Across remaining parts of the discussion area through the daylight hours of Sunday, flow will be weak, and numerous low-level convergence zones are expected to develop. Along these, a few brief/weak tornadoes are possible, given low cloud bases and decent low-level instability. Locally heavy rainfall will be possible too, given little or no storm motion. Brief gusty winds and hail will also be possible.

CG lightning may become locally frequent for short periods of time almost anywhere in the discussion area on Sunday through peak heating.

This is a long-duration discussion to cover the risks for both tonight (in south-western areas) and through daytime Sunday (across the whole of the discussion area).

Last updated by RPK at 01:03 BST Sunday 16th May 2021

Severe thunderstorms

TORRO defines a severe thunderstorm as producing one or more of the following:
  • one or more tornadoes and / or waterspouts
  • hail intensity of at least H3 at ground level
  • non-tornadic winds gusting to 55 mph or more at surface (but which are not part of synoptic-scale straight-line winds of such velocities)
Thunder/lightning does not necessarily need to be present for any of the conditions listed above to occur.

See also...

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