Storm Forecast
Valid: Mon 24 Sep 2007 06:00 to Tue 25 Sep 2007 06:00 UTC
Issued: Sun 23 Sep 2007 22:03
Forecaster: GROENEMEIJER

SYNOPSIS

Monday at 06:00 UTC, at 500 hPa, a broad ridge extends from the Baltic States to southern Italy and a weak trough is almost stationary over the western Black Sea. A weak trough stretches from the Gulf of Genua to just south of the Balearics. Meanwhile, an intense amplifying trough over the eastern North Atlantic moves eastward. An embedded shortwave trough over the Irish Sea is preceded by a cold front in the lower troposphere over Britain. This front is expected to make rapid eastward progress and be located along a line from northern Sweden to eastern parts of Germany and the Alps and further to the southwest into northern Spain. The shortwave trough has by then lifted northward being located over central Norway leaving the longer-wavelength trough filled with cold polar air over the western European continent.

DISCUSSION

Western and central Meditterranean....
The weak trough over the area is expected to move eastward and intensify slightly. Ahead of the trough system, mass convergence will likely deepen the moist boundary layer and weaken convective inhibition sufficiently to allow for organized thunderstorms to form.
Current thinking is that Tyrrhenean Sea, Sicily, Malta, the waters south of Sardinia and parts of NE Algeria and Tunesia will see the highest coverage of storms. Given that deep-layer wind shear is expected to be in the 15-20 m/s range, a few storms may become rather well-organized. A few severe wind, large hail events are expected, while tornadoes cannot be fully excluded either.

France, Switzerland, Germany...

Within the prefrontal air-mass, a few 100's of J/kg of CAPE are expected to form during the day in response to solar heating and ongoing advection of relatively moist air while mid-level temperatures gradually decrease. As a result,. a few thunderstorms will likely form in the afternoon. Low amounts of CAPE and only moderate wind shear suggest that the threat of severe weather will be low, not even warranting a level 1.

Irish Sea, English Channel, North Sea...

In the post-frontal air-mass, unstable air will be advected over waters that are quite warm, which will probably enable convection to become rather deep and thundery, especially where enhanced by coastal convergence. Severe weather nevertheless appears rather unlikely.