Storm Forecast
Valid: Fri 06 Nov 2009 06:00 to Sat 07 Nov 2009 06:00 UTC
Issued: Thu 05 Nov 2009 21:31
Forecaster: TUSCHY

A level 2 was issued for Montenegro and N-Albania mainly for excessive rainfall.

A level 2 was issued for S-Italy mainly for large hail, severe wind gusts, tornadoes and excessive rainfall.

A level 1 was issued for the Ionian Sea, parts of the Adriatic Sea, the coastal areas of W-Greece, Albania, parts of Bosnia and Herzegovina, parts of Serbia and Montenegro mainly for severe wind gusts, large hail, tornadoes and excessive rainfall.

A level 1 was issued for SW-UK, NW/W-France mainly for severe wind gusts.

SYNOPSIS

First trough over the central Mediterranean remains on site, whereas another, potent trough approaches Scotland, Ireland and UK from the NW during the latter part of the forecast period. This pattern causes unsettled conditons over most parts of Europe.

DISCUSSION

... Montenegro and north Albania ...

A favorable pattern for persistent upslope flow along the luv-side of the ragged orography evolves with intense rainfall amounts.

At upper levels, the southern Adriatic Sea will be placed beneath a NNW-ward building WAA regime, with a strong streak clearing the Adriatic Sea towards the northeast and a subtropical streak to the south. This double jet configuration causes a prolonged period of upper divergence over the area of interest.

A strengthening but still ill defined vortex evolves over N-Italy. Attendant pressure gradients over the Ionian and Adriatic Sea increase with 20-25m/s southerly winds below 3km. A tongue of very moist air advects towards the coast of Montenegro and Albania. Either repeatedly showers/thunderstorms due to training or a backbuilding MCS affect the area during the forecast with heavy precipitation, locally exceeding 100mm/day. Another concern is the quality of the airmass below 3km, which is characterized by abundant LL CAPE, low LCLs and significantly increasing shear along the coast, so tornadoes are possible. During the night, the heavy rain and severe risk builds southwards, towards the west coast of Greece.

... S-Italy ...

During the daytime hours, adequate shear and CAPE overlap result in organized thunderstorm chances with multicells and supercells. Severe wind gusts, large hail and tornadoes are all forecast over Sicily, S-Italy and the Ionian Sea. The cold front is slow moving, so excessive rain is possible. The main risk will move offshore during the evening hours.

... NW/N-France and UK ...

The attention turns to the cold front passage over SW/S-UK and NW/N-France at roughly 15 UTC onwards. A prefrontal tongue of somewhat enhanced moisture is forecast beneath the left exit of an intense 70m/s mid-level streak. Therefore, a line of enhanced convection is possible, accompanying the cold front passage. A more distinct intrusion of dry mid-level air is not seen in latest model runs, which limits additional potential instability build-up, which could result in mostly shallow convection and limited lightning activity. Nevertheless, a low thunderstorm probability area was introduced, also due to the postfrontal activity. LL wind field is strong enough for severe wind gusts next to an isolated tornado, mainly along bowing segments. The risk spreads southwards and affects the west coast of France during the morning hours.