Convective Outlook: Wed 14 Jun 2023 |
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What do these risk levels mean? |
Convective Outlook
VALID 06:00 UTC Wed 14 Jun 2023 - 05:59 UTC Thu 15 Jun 2023
ISSUED 06:10 UTC Wed 14 Jun 2023
br> br>ISSUED BY: Dan
An upper ridge will stretch from Scotland to Scandinavia on Wednesday, with a ridge axis also extending southwards across western Britain to Iberia. A very dry airmass will cover many parts of the British Isles, with any deep moisture largely restricted to W/SW Ireland and NW Scotland. Therefore it is these are most likely to have the potential for deep convection.
Once early low cloud and fog clears Munster, strong surface heating through the day should yield 1,000 - 1,500 J/kg MLCAPE across portions of Munster and Connacht, given near-surface temperatures expected to peak in the 24-26C range with dewpoints around 16-18C. In a similar fashion to Tuesday, low-level convergence will increase on the northeastern flank of a rather slack surface low as east/southeasterly winds strengthen through the day across Ulster and Leinster, the main difference being the location of the surface low will be shifted further to the southwest roughly in the vicinity of Shannon. This, in conjunction with sea breeze convergence developing along the west coast of Munster and Connacht and ascent on the forward side of an upper upper trough grazing SW Ireland, will likely aid the development of scattered but rather active thunderstorms during the afternoon and evening hours, migrating northwestwards with time and perhaps upscaling once again into a more organised cluster for a time. Despite some backing of the lower tropospheric winds, effective shear will still be fairly weak (around 10kts) and so the main concern is the risk of surface water flooding given relatively slow storm movement and potential for multiple cells to train over similar areas. Gusty winds to 40mph and marginally-severe hail may also occur near the strongest cells. In addition, a fairly robust sea breeze - perhaps reinforced by outflow - advancing inland either side of the Shannon estuary and through Limerick may enhance low-level convergence/vorticity and provide the opportunity for a couple of funnel clouds.
Elsewhere, an increasingly unstable environment is anticipated across both NW Scotland and portions of Wales, SW Midlands and Cen S / SW England in response to surface heating. The greatest instability will be in NW Scotland, where low-level convergence and/or orographic uplift may allow a couple of isolated heavy showers/thunderstorms to develop, but unlikely to be as widespread or as intense/long-lasting as those of recent days. In southern Britain, very dry profiles with a deep and well-mixed boundary layer will once again limit the potential for showers, except where particularly strong forced ascent from the surface occurs (such as sea breeze just inland from the south coast, or additional lift from high ground) which may just be sufficient to generate an isolated, brief heavy shower/weak thunderstorm, perhaps aided by a subtle PV strip drifting gradually northeastwards across SW Britain.