Valid: Tue 01 Nov 2011 06:00 to Wed 02 Nov 2011 06:00 UTC
Issued: Mon 31 Oct 2011 17:10
SYNOPSIS and DISCUSSION
A quasi-stationary upper low remains in place over Tunisia and surrounding areas. Overall thermodynamic set-up seems marginal at best so only a 15-% thunderstorm area was introduced. Best thunderstorm chances evolve along a moisture tongue, which runs from NE-Algeria to Malta. Weak shear supports slow storm motion, so any shower/thunderstorm has a good chance to produce locally heavy rainfall amounts. The conditions over far NE-Algeria and N-Tunisia are probably a borderline level 1 situation, but mixed QPF signals in model fields and yesterday's limited thunderstorm coverage (with similar conditions) do not yet require an upgrade.
The next spot for thunderstorm development is bound to the westerlies, which continue to reveal a progressive pattern over NW/N-Europe. A weakening upper trough crosses UK during the forecast. Due to cold mid-levels atop some residual maritime BL air, weak MLCAPE signals are present. We did not issue a thunderstorm area for the English Channel due to the limited time frame of occurrence. Also the conditions become worse as the upper trough flattens during the day. Any thunderstorm will be short-lived and non-severe.
A plume of roughly 500 J/kg MLCAPE is present west of the Balearic Islands due to cool mid-levels atop ~ 18°C SST. Shear is on the low end side of the spectrum with 5-10 m/s 0-6 km bulk shear forecast. Some marginal strengthening is expected with 10-15 m/s DLS during the night hours. This may be supportive for a localized better organized thunderstorm with marginal hail and strong wind gusts. Storms continue during the night.
An extensive low starts to intensify west of the Bay of Biscay/Iberian Peninsula, but the main activity remains west of our forecast area until 06 Z.
Surface high pressure/ridging prevents thunderstorm activity over the rest of Europe.