Convective Outlook: Sat 24 Oct 2020
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Sat 24 Oct 2020 - 05:59 UTC Sun 25 Oct 2020

ISSUED 07:46 UTC Sat 24 Oct 2020

ISSUED BY: Dan

A cold front will migrate steadily eastwards across Britain on Saturday, with a marked thermal gradient and wind veer. This, coupled with a strongly-sheared environment suggests scope for line segments to develop, increasingly so from mid afternoon into the evening hours across parts of central, southern and eastern England. This squall line, perhaps broken at times, will bring the threat of brief periods of torrential rain and strong gusts of wind, including the potential for one or two isolated tornadoes. Much of the time the embedded convection will likely be fairly shallow in height, suggesting a low risk of lightning (5-10% chance), however there may be scope for deeper convection to occur along the squall line across S / SE England and into East Anglia later in the day which would increase the potential for a few lightning strikes (10-15%).

Immediately behind the cold front, guidance suggests the potential for another area of showery rain, with embedded convection on its southern/eastern flank, to swing northeastwards across parts of England and Wales during the evening hours. The strongest convection on the southeast side of this cluster could produce a corridor of very strong winds, most likely across parts of SW England / SE Wales and into the Midlands. An isolated tornado is also not ruled out from this feature either.

A SVR has been issued for Saturday afternoon/evening for the potential for locally damaging winds as the squall line moves through along the cold front, and also with any post-frontal convection during the evening hours, plus the risk of an isolated tornado.

Throughout Saturday across western Scotland, and increasingly widespread overnight across Ireland and into western Britain, a cold pool will overspread relatively warm SSTs, creating an environment with steep mid-level lapse rates and up to 500 J/kg CAPE. Numerous showers are likely as a result, some capable of producing copious amounts of hail, some gusty winds and sporadic lightning - more especially on Saturday night as instability increases. As such, a low-end SLGT (25-30% chance) has been introduced along some western coasts.