Convective Outlook: Mon 09 May 2022
LOW
SLGT
MDT
HIGH
SVR
What do these risk levels mean?
Convective Outlook

VALID 06:00 UTC Mon 09 May 2022 - 05:59 UTC Tue 10 May 2022

ISSUED 05:01 UTC Mon 09 May 2022

ISSUED BY: Dan

An upper ridge slowly clears to the southeast on Monday, placing the British Isles increasingly under the forward side of an Atlantic upper trough. Frontal rain will affect Ireland, Northern Ireland and Scotland for much of the day (possibly with embedded linear features), however clearing in W / NW Ireland during the afternoon with some opportunity for renewed surface heating ahead of the secondary cold front. Cold air aloft overriding a relatively warm/moist surface airmass (13-15C with dewpoints 10-12C) could yield a few hundred J/kg CAPE. Convection/showers may develop in the pre-frontal environment, but may be somewhat restricted in height (~14,000ft) by a substantial dry intrusion. Nonetheless, even this relatively shallow layer will be strongly sheared (30-40kts) given the very strong mid/upper level jet. Forecast profiles reveal fairly unidirectional winds with height, and so convection will likely become rather linear in nature but capable of producing squally winds. That said, some backing of the low-level winds (especially SW Scotland) may promote rotating updrafts and hence perhaps a chance of a low-topped supercell.

There is scope for convection to punch higher into the substantial dry layer aloft, this perhaps most likely due to a combination of increasing PVA aloft and forced ascent along the narrow secondary cold front that arrives from the west during the late afternoon and evening hours. Should this occur, then some rather active and longer-lived thunderstorms may occur, more especially NW Ireland / Northern Ireland into W / SW Scotland given the longer land-track and more favourable overlap of key ingredients. If thunderstorms do develop they will likely weaken by late evening as they move into central Scotland. The strongest cells may produce both marginally-severe hail and wind gusts, but have refrained from introducing a SVR at this stage. Shallower convection still capable of producing brief heavy rain and gusty winds will be possible farther down the cold front across the remainder of Ireland during the evening hours, drifting across the Irish Sea overnight, but the risk of lightning here is much lower.

Finally, the post-frontal environment will be characterised by cold air aloft atop relatively warm SSTs and more cellular convection, with numerous showers spreading into western portions of Ireland and Scotland overnight that may produce odd isolated lightning strikes - the deepest convection is likely near the Outer Hebrides and so here the lightning risk is highest (but still sub-SLGT).