Storm Forecast
Valid: Thu 16 Oct 2008 06:00 to Fri 17 Oct 2008 06:00 UTC
Issued: Wed 15 Oct 2008 17:07
Forecaster: GATZEN

SYNOPSIS

Rather sharp upper trough moves eastward over northern and central Europe during the period. It amplifies into Mediterranean as it connects with a weak upper trough over west Mediterranean. In the wake of the trough, a high moves to Bay of Biscay and ridges into British Isles. Another ridge is located over south-eastern Europe. While warm low-level air mass extends from Iberian Peninsula to most of west Mediterranean and Adriatic, cold polar air mass spreads into western Europe in the wake of a cold front during the period.

DISCUSSION

Northern Adriatic

Trough axis of the sharp European trough moves eastward and leads to cyclogenesis south of the Alps. As a consequence, southerly flow and warm air advection is expected over northern Adriatic region during the evening and night hours until the cold front will spread into Adriatic Sea during the end of the forecast period. Although low-level air mass is actually quite dry, latest soundings indicate that substantial boundary-layer moisture is located to the west and south that will likely spread north-eastwards on Thursday, and 10 g/kg low-level mixing ratio seems to be likely.

As the upper trough axis approaches, upper height falls will likely lead to destabilization over northern Adriatic, and latest model output indicates some instability forming during the night hours. In the range of strong upper level jet streak curving around the trough axis, quite strong QG forcing will occur as indicated by latest GFS model output.

Although EL temperatures are forecast to be rather warm, expect that thunderstorms will form during the late evening that will go on during the night while spreading south-eastward. Well-developed multicells are likely given 20 m/s DLS. Embedded mesocyclones are also possible as 0-3 km SRH will be in the 150 m²/s² range due to southerly low-level winds and westerly jet aloft. Locally large hail and severe wind gusts are forecast. Storms will likely merge into a mesoscale system with embedded convection moving eastwards into northern Balkans. Intense precipitation and local flash flooding will be possible with this system as QG forcing will persist throughout the night.

Central Europe, Alpine region

Along the cold front, a shallow convective line is forecast to develop. Instability is forecast to be quite shallow and deep convection will be possible only over isolated places.

Southern and western North Sea

Trough axis will cross the North Sea until the afternoon and evening hours. Given quite warm sea surface, cold polar air mass will be unstable, and convection will likely develop. Given strong low-level buoyancy and 10 m/s LLS in the range of the coasts, tornadoes are not ruled out. Most significant threat will be severe wind gusts in the range of bowing lines. Soft hail may also be possible. Convection will likely spread eastward over Denmark later on. Severe threat is expected to weaken over the Baltic Sea.