Convective Outlook: Wed 06 May 2020
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Wed 06 May 2020 - 05:59 UTC Thu 07 May 2020

ISSUED 20:06 UTC Tue 05 May 2020

ISSUED BY: Dan

Upper ridge across the British Isles will slowly retreat to the Continent on Wednesday, allowing an upper low over the Atlantic to the west of Biscay to extend a trough towards Ireland/western Britain. The net result is a strengthening southerly flow, advecting a relatively high ThetaW airmass northwestwards from the Bay of Biscay across the Celtic Sea and towards Ireland. The combination of gradual warming of the profile at ~900mb combined with cooling of the mid-levels (500-700mb), most pronounced on Wednesday night as an upper trough axis swings northwards, will ultimately steepen mid-level lapse rates and increase mid-level instability. 

Several impulses will aid in the development of showery outbreaks of rain through Wednesday and Wednesday night, running from Cornwall / Isles of Scilly northwestwards towards southern Ireland. Initially instability will be fairly weak, and while a few isolated lightning strikes cannot be ruled out the risk in any one location is relatively low. However, with each passing hour, and as the main trough axis approaches, mid-level instability will gradually increase to 100-300 J/kg CAPE bringing an increasing risk of some sporadic lightning by the afternoon and evening hours - primarily over the open waters of the Celtic Sea, but also extending inland across parts of Ireland during the evening and night hours. Confidence is not particularly high in the exact coverage of lightning, but have tentatively introduced a low-end SLGT where lightning is considered most likely to occur, but a few isolated strikes may be possible elsewhere.