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Convective/Thunderstorm Discussion Spring/Summer 2018
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From what I can make out the American models bring the front inland and the European hold it off/ close to the coast. Big difference in the outcome. American say a line of rain and possible thunderstorms developing in the afternoon / early evening with all that diurnal heating available, European: drizzle / light rain perhaps. MT was mentioning that this will become a Nowcast so the Satellite and obs will tell more later. Met Eireann siding with the European .
For what it is worth here is the potential thunderstorm set up.
ECM showing light rain at best as the weak front drifts on to the coast and slowly inland.
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Storms moving up over the Bay of Biscay, affecting the SW UK tomorrow morning . Latest models not showing thunderstorms for Ireland. ECM showing rain reaching the S coast Sun night/ early Mon morning. Worth keeping an eye on though.
https://twitter.com/metoffice/status/1013121490177482753
Day 2 Convective Outlook
VALID 06:00 UTC Sun 01 Jul 2018 - 05:59 UTC Mon 02 Jul 2018
ISSUED 14:35 UTC Sat 30 Jun 2018
ISSUED BY: Dan
Upper low will continue to be centred near NW Iberia, with a couple of shortwave impulses emanating from N Iberia and W France drifting N then NW on its eastern flank towards S / SW England. The first shortwave will be responsible for aiding the development of scattered elevated thunderstorms over Devon/Cornwall/Scilly first thing on Sunday morning, as it engages with a plume of high ThetaW advecting from France into southern Britain. This activity will tend to clear northwestwards across the Celtic Sea, though may be followed by renewed pulses of elevated showers/thunderstorms over similar areas.
Farther east, a complicated picture evolves as the moisture / instability plume nudges northeastwards, with potential for both elevated and surface-based thunderstorms over parts of Cen S England and the West Country during the afternoon. Dewpoints of 17-20C will be possible across the area, yielding up to 1,000 J/kg CAPE with PWAT values of 35-40mm. However, there is considerable uncertainty amongst NWP guidance due to the differences in handling the shape / orientation of the ThetaW plume, and any hangback of cloud following morning elevated convection - both of which will affect how much instability may be available.
Nonetheless, it seems likely that a few thunderstorms will develop over parts of Cen S England and the West Country during Sunday afternoon, drifting into the SW Midlands and S Wales - though probably with a weakening trend. If the higher values of instability do develop, then hail up to 1.5cm in diameter will be possible, along with frequent lightning and the threat for localised surface water flooding - especially given the current dry ground. In all cases, elevated thunderstorms initially pose a threat for exacerbating the wildfire risk given lightning occurring over tinder-dry vegetation, before any substantial rainfall makes it to the ground.
Further scattered elevated showers / thunderstorms may continue to develop in a rather random fashion during the evening and overnight hours over parts of Wales / West Country / Midlands / Cen S England, as subtle forcing aloft engages the remnant instability plume in place.0 -
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Convective Outlook
VALID 06:00 UTC Wed 04 Jul 2018 - 05:59 UTC Thu 05 Jul 2018
ISSUED 20:07 UTC Tue 03 Jul 2018
ISSUED BY: Dan
Elongated upper low will drift across the British Isles on Wednesday, gradually merging with the larger-scale Atlantic upper trough. The focus initially will be on pockets of elevated convection over S and SW England during the morning hours, although with weak instability any lightning activity should be fairly isolated. By the afternoon, strong surface heating and low-level convergence (due to the slack surface flow) will shift the focus to surface-based developments - primarily over S + E Ireland, Scotland into N England, and S / SW England into S Wales and the S Midlands. A few isolated showers may develop, the convection perhaps deep enough locally for a few lightning strikes - though the marginal instability, weak shear and sparse coverage precludes the issuance of a SLGT. Isolated showers may continue to develop during the evening hours, particularly near M4 corridor / S Wales, though most will generally decay overnight as nocturnal cooling commences. Main threats will be locally high rainfall totals, given slow movement of showers and very dry ground - especially so on roads where dust deposition on the road surfaces over the past few weeks may make conditions rather slippery.0 -
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The ECM 0Z throws in a very active convective day next Fri . A long way off for sure with the way the models have been chopping and changing but worth keeping an eye on. Atm anyway showing us under an upper trough /low, with temps low to mid 20's, High Theta E readings. Probably too early even posting this but it looks interesting.
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Meteorite58 wrote: »The ECM 0Z throws in a very active convective day next Fri...
...the 13th! :eek:
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