Convective Outlook: Thu 16 Mar 2023
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Thu 16 Mar 2023 - 05:59 UTC Fri 17 Mar 2023

ISSUED 07:18 UTC Thu 16 Mar 2023

ISSUED BY: Dan

An upper ridge over S/SE Britain will gradually clear eastwards across mainland Europe on Thursday, allowing an Atlantic upper trough to advance from the west. This places the forward side over the British Isles, with the main focus for deep convection in the post-frontal environment over Ireland as cooling aloft (T500 down to -25C) associated with a shortwave overlaps favourably with a reasonably moist low-level airmass (Td 10-11C) during peak diurnal heating. As such, profiles will become increasingly unstable during the afternoon hours, yielding 200-400 J/kg MLCAPE. As low-level winds ease somewhat, a SW-NE confluence zone is expected to develop and will likely provide the focus for scattered heavy showers to form, running northeastwards from Connacht and N and W Leinster to Ulster, and eventually into SW Scotland later. 

Forecast profiles reveal a slight warm nose between 550-700hPa that could inhibit (or at least slow parcels), and this casts some uncertainty over how deep convection may be (and subsequent lightning activity). At the very least ELTs should reach/exceed -15C but could potentially be around -40C. Strong southwesterly flow aloft will result in 30-45kts DLS, the winds fairly unidirectional but increasing numerically with height. Assuming deep convection can develop in the strongly-sheared environment, then there is scope for some organised cells that could potentially produce some marginally severe hail. The tornado threat will be somewhat limited by fairly unidirectional wind profiles, but that said some backing of the low-level wind field is possible as the afternoon progresses, particularly as cells move across Ulster and towards SW Scotland. Cells training over similar areas have the potential to produce locally high rainfall totals. A low-end SLGT has been tentatively introduced, but as mentioned concerns exist about overall depth of convection and how much lightning activity actually occurs. Also mindful of the relatively short temporal window of meaningful surface heating at this time of year.