Convective Outlook: Sun 31 Oct 2021
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Sun 31 Oct 2021 - 05:59 UTC Mon 01 Nov 2021

ISSUED 07:07 UTC Sun 31 Oct 2021

ISSUED BY: Dan

SUMMARY: The greatest risk of a couple isolated tornadoes will be on Sunday morning. Local strong/damaging winds will be possible throughout the forecast period. The greatest risk of sporadic lightning will be during Sunday evening/night.

A frontal zone/band of rain will continue to track northwards and eastwards across Britain, while wrapping around a surface low drifting across Northern Ireland to bring persistent rain back into western Ireland and later into N Wales/NW England. Ahead of this front, a pronounced low-level jet will exist with backed surface winds and limited CAPE. Pockets of embedded convection/line segments are likely, primarily south Wales and into portions of England, which will be capable of producing damaging gusts of wind and perhaps a couple of tornadoes. The strong low-level shear may encourage small-scale circulations to develop, and this may heighten the risk of an isolated tornado. This risk may be greatest both close to the south coast (where the overlap of CAPE and shear will be greatest) but perhaps also in a SW-NE corridor near a wave that may develop along the front - current thinking is this zone will exist from the Wiltshire/Hampshire area northeastwards to the Humber, but there is room for some margin of error in the track +/- a county. A broad SVR has been issued for the risk of local wind damage from either straight-line winds or isolated tornadoes, but most areas within this area will not experience these conditions.

As the frontal rain clears northeastwards there may be a brief lull before showers develop widely near western coasts initially, and then feeding across the English Channel. Given temperatures inland of 12-14C for a time, additional showers are likely to develop either inland or feed well-inland during the afternoon, and a few isolated lightning strikes will be possible almost anywhere from SW Scotland, the Irish Sea and across Wales, Midlands and southern England - but the risk in any one location is rather low. With very strong westerly winds just above the ground, these may be brought down to the surface near any modestly-heavy showers and so the potential for squally/strong gusts of wind will remain.

The environment with the deepest/most intense convection, and hence greater lightning potential, will tend to approach SW England / S Wales during the second half of the afternoon, and expand eastwards through the English Channel during the evening and night hours. Sporadic lightning is likely in places - initially the WSW steering flow will drive showers into southern coastal counties, however this may shift more to the WNW later in the night as the main trough axis swings through, placing the Channel Islands at greater risk.