Convective Outlook: Tue 22 Mar 2022
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Tue 22 Mar 2022 - 05:59 UTC Wed 23 Mar 2022

ISSUED 07:17 UTC Tue 22 Mar 2022

ISSUED BY: Dan

On Tuesday, the UK/Ireland sits on the western flank of a large upper high cell centred over Poland. Diurnal heating with surface temperatures of 17-19C widely may yield a couple hundred J/kg CAPE. A weak thermal plume, having originated from France overnight, is expected to continue to drift northwards through Tuesday and provide the focus for a few isolated heavy showers during the afternoon and evening hours. However, NWP guidance varies as to how much low-level moisture may be available; those with 2m dewpoints of 9-11C widely are naturally keenest to develop deep convection, whereas other solutions with lower dewpoints (generally 7-9C) struggle to maintain any deep convection and therefore offer very few showers. There is also very little forcing other than a subtle shortwave drifting northwestwards coupled with some southeasterly upslope flow over the Chilterns/Cotswolds/Pennines etc that may aid in forced ascent.

Nonetheless, convective cloud will likely bubble-up through the day, and make several attempts to gain some height. Forecast profiles suggest cloud tops could reach up to 18,000ft if successful, but will be battling a lot of dry air aloft. There may be scope for a few isolated heavy showers to develop, more especially second half of the afternoon into the early evening, and depending on the depth of convection the odd isolated lightning strike cannot be ruled out. Speed shear is rather weak (stronger over Ireland), suggesting pulse-type mode, although any cells that can develop close to the east coast may benefit from substantial low-level directional shear (but likely a colder boundary layer due to the cool onshore flow). Showers will generally decay later in the evening, but may persist overnight in Scotland as the weak thermal plume continues to drift northwards.