Convective/Thunderstorm Discussion: Summer 2022
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Met.ie language also quite juicy for tomorrow.
"A few isolated heavy showers and thunderstorms may develop throughout the day, but they will increase in coverage through the later afternoon and evening. The most intense slow-moving deluges, will cause some spot flooding and intense lightning"
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Wow
Day 1 Convective Outlook
VALID 06:00 UTC Sun 14 Aug 2022 - 05:59 UTC Mon 15 Aug 2022
ISSUED 07:02 UTC Sun 14 Aug 2022
ISSUED BY: Dan
A rather complex forecast evolution is anticipated on Sunday as an upper low near Biscay merges into a digging upper trough approaching from the Atlantic. A hot, well-mixed airmass covers much of the British Isles, while cooling aloft occurs as the upper trough advances gradually eastwards. The net result is increasingly unstable profiles and the greater chance of thunderstorm development. Given the complex evolution model guidance naturally varies on timing and placement of possible showers/thunderstorms, and this casts some uncertainty.
PVA on the forward side of the Atlantic trough will aid development of thunderstorms across western Scotland on Sunday morning, expanding into central and northern Scotland during Sunday afternoon and early evening, before moving offshore to Orkney/Moray Firth while weakening. These could be quite electrically active for a time, possibly with wind gusts of 40-50mph locally.
Meanwhile, additional surface-based thunderstorms could develop during the second half of the afternoon and into the evening hours in southern Scotland, north Wales, Cumbria, and parts of Ireland (especially southern and eastern areas), aided by low-level convergence and/or orographic forcing. For much of England and Wales profiles are too dry and deeply-mixed, with little support aloft, to generate deep convection, but a few heavy showers/brief thunderstorms may be possible in mid/north Wales where orographic forcing plays a more vital role - but these may struggle to last more than an hour or two. However, for southern Scotland and portions of Ireland, weaker capping and stronger support aloft suggests a greater potential for a few well-scattered thunderstorms to develop in an environment with perhaps as much as 1,000-1,500 J/kg MLCAPE and ~30kts DLS. Therefore, there will be the potential for strong to severe thunderstorms if cells can remain relatively discrete, capable of producing large hail, torrential rain and gusty winds. CAM guidance suggests the potential for one or two storms to exhibit rotating updrafts, which would enhance the hail potential and cell longevity. A SVR has been introduced to highlight the risk of large hail, perhaps 2-3cm in diameter in the most intense, well-organised storms, for wind gusts of 40-50mph and flash flooding. The relatively high cloud bases (at least initially) and weak low-level flow should generally limit the tornado threat.
As the Atlantic upper trough continues to advance eastwards, renewed waves of thunderstorms will be possible during the overnight hours, particularly in parts of Ireland and Scotland. Greatest focus appears to be central, southern and eastern Ireland where thunderstorms may grow upscale into a larger complex, perhaps aided by strong outflow/cold pool generation. The large hail threat will probably reduce should this evolution occur, but flash flooding and gusty winds will continue to be a threat. Elsewhere, a few showers/odd thunderstorm cannot be ruled out in Wales / NW England during the overnight period, and also perhaps towards coasts of SE England / East Anglia as PVA on the leading edge of the earlier Biscay upper low advances from the near-Continent - although confidence on much in the way of activity is too low to warrant a SLGT at this
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