Storm Forecast
Valid: Sat 06 Dec 2008 11:00 to Sun 07 Dec 2008 06:00 UTC
Issued: Sat 06 Dec 2008 11:07
Forecaster: DAHL

SYNOPSIS

Deep quasi-stationary longwave upper trough is covering central Europe, extending southwards well into the Mediterranean. At the SW periphery of this feature, a cut-off cyclone is slowly moving southeastwards towards the NW Iberian peninsula, attached to it is a plume of warm/moist air which is spreading into western Iberia. Another cut-off cyclone is present over Libya, simulated to merge with the large-scale trough, resulting in an eastward acceleration of the cut-off cyclone, boosting the quasi-geostrophic forcing downstream of this feature.

DISCUSSION

... Aegean region ...

Ahead of the lifting Libyan upper low, strong DCVA-related ascent is simulated, so that thunderstorms should form despite the strong capping implied by the 00Z LGIR (Crete) ascent. Deep-layer shear should exceed 30 m/s, with low-level shear locally in excess of 10 m/s, which should be sufficient for severe evolution. Only weakness seems to be the limited amount of CAPE as well as strong capping which could both limit the storm coverage. Still, well-organized multicells and bowing segments, likely also containing mesocyclones, are anticipated. Expect damaging wind gusts, large hail, and possibly a brief tornado or two with the strongest cells. The severe weather threat should persist throughout the night.

... extreme NW Spain ... SW Gulf of Biscay ...

Scattered thunderstorms appear to be present beneath the center of the upper cyclone which is moving towards the Iberian peninsula. The bulk of the convection should exist in weakly unstable and weakly sheared environment, and consequently the severe threat should be rather low.

... Adriatic Sea ...

It seems that a few waterspouts may occur with the convection over the N Adriatic as low-level lapse rates are steepening during the period. These tornadoes should be too isolated to warrant a categorical outlook.

... central portions of Europe ...

Sporadic lightning may occur over central Europe with showers developing in the relatively deep polar air. However, warm cloud tops and a very low degree of organization due to a lack of vertical shear suggest that lightning activity will remain too low for a thunderstorm area.