Convective Outlook: Fri 17 Mar 2023
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Fri 17 Mar 2023 - 05:59 UTC Sat 18 Mar 2023

ISSUED 08:40 UTC Fri 17 Mar 2023

ISSUED BY: Dan

An upper trough over the Atlantic will drift slowly eastwards across Ireland later on Friday, placing southwesterly flow aloft across the British Isles albeit tending to weaken with time as both the surface and upper pattern slackens. A trailing cold front over SE Britain will provide the focus for some more organised rain on Friday morning as a wave runs northeastwards along the front, generally clearing to the North Sea into the afternoon. A couple of secondary occlusions will drift across Ireland and western Britain, providing the focus for areas of cloud and outbreaks of rain, although these features may tend to fragment and turn more convective through the day. All-in-all, a very messy pattern is anticipated on Friday which casts some uncertainty over how much (if any) lightning activity may occur - not least because of fairly large amounts of cloud in places.

Current thinking is portions of the English Midlands into northern/eastern England, and also the Irish Midlands into Connacht will probably have the best potential for deep convection given more cloud breaks/better insolation yielding a few hundred J/kg CAPE in response to diurnal heating (13-15C with Td 9-11C). Forecast profiles suggest convective cloud could potentially reach tops of ~26,000ft. The strongest flow aloft will be over England, where modest DLS of 20-30kts could aid in cell longevity/organisation here, but shear will be rather weak over Ireland resulting in predominantly pulse-type convection. This, in conjunction with fairly tall, skinny CAPE profiles and the risk showers may merge into longer spells of showery rain, may limit much in the way of lightning in Ireland. Similarly, evidence of a warm nose at ~600hPa over England may also restrict the depth of convection.

In addition, elevated convection drifting northeastwards from France and across the English Channel during the late afternoon and evening hours may also provide the focus for clusters of heavy showers/weak thunderstorms over parts of the Channel Islands and perhaps close to the Kent/Sussex coast.