Convective Outlook: Wed 03 Mar 2021
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Wed 03 Mar 2021 - 05:59 UTC Thu 04 Mar 2021

ISSUED 07:26 UTC Wed 03 Mar 2021

ISSUED BY: Dan

An upper low, initially over the western English Channel on Wednesday morning, will drift slowly northeastwards then east-northeastwards to become centred near west London by midnight Wednesday night, then east-southeastwards over the Strait of Dover by 06z Thursday. The associated cold pool will aid in some steepening of the mid-level lapse rates, yielding some weak elevated CAPE - but increasing to a few hundred J/kg CAPE in response to SSTs and any diurnal heating inland. Showery outbreaks of rain will likely slide across parts of central and southern Britain through Wednesday and Wednesday night, although the risk of lightning with this is considered rather low (5% chance). Nonetheless, the slow movement - especially on Wednesday night over parts of East Anglia and/or the East Midlands - could result in some locally large rainfall accumulations.

Rather extensive cloud will likely limit insolation, however some support for breaks in the cloud to develop in south and more especially southwest England which would allow greater surface heating to occur. Here, given the slack surface pattern and a small low centre in the vicinity, low-level convergence coupled with orographic forcing may aid forced ascent to generate a few heavy showers. Forecast profiles are rather saturated with weak shear and limited CAPE, and so the risk of lightning is considered quite low (10% chance) but a few isolated lightning strikes might be possible. The main area of interest is primarily southern counties of England, perhaps as far north as Gloucestershire and encompassing part of south Wales depending on sufficient cloud breaks. The moist boundary layer (low cloud bases) and convergence may allow a few funnel clouds to occur.