Convective Outlook: Wed 08 Sep 2021
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Wed 08 Sep 2021 - 05:59 UTC Thu 09 Sep 2021

ISSUED 06:41 UTC Wed 08 Sep 2021

ISSUED BY: Dan

An upper low over the Celtic Sea will lift slowly northeastwards through Wednesday. On the leading edge, a narrow tongue of relatively high Theta-W will be the main focus for potential lightning activity along an instability axis, and this will gradually migrate northeastwards with time. Initially, the main focus will be over Ireland, SW England and the Channel Islands, moving eastwards across Cen S Eng and S Wales through the day and towards SE England / Midlands during the evening. There is a large amount of uncertainty as to how much lightning activity will occur vs just pockets of showery rain, and this adds difficulty in determining the threat levels to introduce and where.

Realistically, there could be a few odd lightning strikes almost anywhere from various pulses of showery rain during this forecast period. Current thinking is one cluster of heavy rain and elevated thunderstorms will affect the Channel Islands and SW England (especially Devon) during the morning, but possibly weakening (in terms of lightning) towards midday. Another wave may develop over northern France (initially surface-based potentially) and drift across the English Channel towards S / SE England during the afternoon and evening hours, but again perhaps weakening as it tracks further north - however, there could be an uptick of activity inland over the Home Counties late evening/overnight. Elsewhere, there is a small chance of isolated surface-based showers/thunderstorms developing over SW Midlands, SW England (especially N Devon/W Somerset), central Scotland and western Ireland - but in most cases this will be capped and heavily dependent on sufficient surface heating.