Convective Outlook: Sat 29 Apr 2023
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Sat 29 Apr 2023 - 05:59 UTC Sun 30 Apr 2023

ISSUED 06:55 UTC Sat 29 Apr 2023

ISSUED BY: Dan

Beneath a mid/upper-level ridge covering the British Isles, a residual moist low-level airmass will persist across much of England, Wales, Ireland and Northern Ireland on Saturday with dewpoints typically 10-14C. Assuming low cloud and fog erodes through the day, increasing insolation and resultant surface heating may yield >500 J/kg MLCAPE widely, with localised pockets potentially near 1,000 J/kg. This, in conjunction with orographic lift and increasing low-level wind convergence in the slack pressure pattern, may encourage a scattering of heavy showers to develop. Modified forecast soundings suggest ELTs could reach -25C over England/Wales and potentially -40C over Ireland. However, as was the case on Friday, subsidence aloft in the vicinity of the aforementioned ridge casts some uncertainty over how deep/sustained convection may be, and therefore the likelihood of any lightning.

For England and Wales, the main area of interest is N + E Wales across the Midlands to Lincolnshire, including southern portions of northern England. Here, a few isolated lightning strikes may be possible from the strongest cells that can become sufficiently deep/sustained - most likely over NE Wales/NW Midlands/NW England, where a low-end SLGT was introduced. An arguably more favourable environment is anticipated across Ireland/Northern Ireland, especially towards the evening as the upper ridge axis departs to the east and PVA on the forward side of an Atlantic upper trough approaches from the west. While speed shear may not be that strong (~20kts), backed low-level winds and therefore curved low-level hodographs across Ulster especially may yield a degree of low-level rotation with any long-lasting cells. With only slow cooling of the boundary layer, profiles will likely remain unstable well into the evening, and as such heavy showers/a few thunderstorms may continue to develop even after dark, albeit probably with decreasing lightning risk by late evening.