Convective Outlook: Thu 15 Jun 2023
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Thu 15 Jun 2023 - 05:59 UTC Fri 16 Jun 2023

ISSUED 06:48 UTC Thu 15 Jun 2023

ISSUED BY: Dan

Broad upper ridging stretches from Scandinavia, across the British Isles and down to Iberia on Thursday, with slightly lower heights aloft across both western Ireland and eastern England. A moist airmass persists across the bulk of Ireland, having been restricted to southwestern areas on Wednesday, and will provide the focus for another day with shower/thunderstorm potential. Areas of low cloud and patchy fog, most extensive across Munster and southern portions of both Connacht and Leinster, should erode through the morning with diurnal heating then likely to yield MLCAPE on the order of 1,000 J/kg given expected maximum temperatures of 23-26C and dewpoints 14-17C. CAM guidance suggests initiation around mid-afternoon, with a gradual increase in the number of scattered heavy showers and thunderstorms developing during the late afternoon and evening hours. A slack surface low is forecast to develop in central/west Ireland, and so like previous days the greatest potential for thunderstorms to grow into a larger cluster will be on its north/northeastern flank where strengthening low-level convergence may develop as easterly winds from the Irish Sea meet a SSEly wind further inland. Therefore, have introduced a MDT to highlight the area where lightning activity may be somewhat more widespread, especially later in the day and into the evening hours. Weak flow aloft will once again result in meagre shear, and given CAPE is a notch down on recent days it is likely hail for the most part should be sub-severe. The main threat, given PWAT 25-30mm and slow storm motion, is the risk of local surface water flooding. Gusts of 30-40mph may accompany the strongest cells.

Across Britain, profiles will once again be very dry however a slightly cooler and moister airmass will be present across England and Wales than recent days, while residual moisture persists across NW Scotland, and as such diurnal convective cloud may have a better chance of attaining height and longevity where forced ascent exists, either from sea breeze convergence just inland from the coast, or better still from orographic uplift (e.g. Wales, SW England). A few of these may just produce a few lightning strikes for a time, this seems most likely over Wales and perhaps far NW Scotland where a couple of low-end SLGTs were introduced. Any isolated showers will generally decay through the evening hours, although a few odd ones may linger/develop overnight in NW England and the West Midlands.

Finally, during Thursday night a substantial push of relatively high Theta-W air, originating from the subtropics, will approach the Celtic Sea and eventually southern Ireland. This will be accompanied by areas of showery rain which may contain a few embedded thunderstorms, although the extent of lightning activity with this is unclear - but it is possible a few strikes may occur close to S/SW Ireland late in the night, and perhaps also close to the Munster and Donegal coast as additional showers develop nearby overnight before moving offshore to the northwest.