Storm Forecast
Valid: Wed 17 Oct 2007 06:00 to Thu 18 Oct 2007 06:00 UTC
Issued: Tue 16 Oct 2007 16:27
Forecaster: GATZEN

SYNOPSIS/DISCUSSION

A strong upper trough evades into central Europe, and cold air mass spreads southward. Warm air mass ahead of the cold front is forecast to be rather stable, and thunderstorms are not expected over most places. Best potential exists over central Scandinavia at the beginning of the period. Along the cold front occlusion, a tongue of moist low-level air mass will spread into this region, while upper cooling and strong QG forcing is forecast in the range of the cyclonic exit of the upper jet streak. This will likely result in some instability coupled with strong DLS and also favorable veering profiles. Current thinking is that a broad precipitation band will form, with embedded convection and some thunderstorms included. Although strong low-level buoyancy is not expected, some cells may root to the boundary layer. Given strong low-level vertical wind shear and more than 150 J/kg 0-1 km SRH, tornadoes are not ruled out. Convection will gradually weaken during the day given weakening instability ahead of the front.

In the range of the following trough, cold and unstable air mass is forecast over the North Sea and southern Baltic Sea. CAPE and strong vertical wind shear are forecast to be in place over Denmark, and the Baltic Sea, where unstable air mass will be underneath the cyclonic flank of the upper jet streak rotating around the upper trough. Amount of instability is relatively uncertain at this time, and it may be limited to lower levels, given warm air mass aloft in the range of the frontal boundary. Additionally, forcing is also limited behind the front given low-level divergence initially. Forcing can be expected in the range of the following trough axis that enters the region during the night, but vertical wind shear is strongly decreasing by this time due to latest models. Altogether, severe thunderstorms are not expected during the period, although isolated severe wind gusts are not excluded.

Another region with unstable air mass is western Mediterranean as indicated by latest ascends. Rather moist low-level air mass and neutral to slightly unstable lapse rates are present. Thunderstorms will likely develop in the range of a weak trough. Given almost weak vertical wind shear, severe thunderstorms are not forecast. Isolated strong winds and marginally hail as well as an isolated tornado are not ruled out completely, though.