Storm Forecast
Valid: Fri 14 Aug 2009 06:00 to Sat 15 Aug 2009 06:00 UTC
Issued: Thu 13 Aug 2009 21:06
Forecaster: TUSCHY

A level 1 was issued for N-Algeria and Tunisia mainly for large hail and severe wind gusts.

A level 1 was issued for Slovenia mainly for large hail.


SYNOPSIS

Numerous troughs affect northern Europe, where a chilly airmass and unsettled conditions persist. Hot and mostly stable conditions can be found over SE-Europe and parts of the Mediterranean.

DISCUSSION

... N-Algeria and Tunisia ...

Embedded in the subtropical jet, a disturbance crosses those areas during the forecast from the west. A dry and well mixed airmass is present over the continent with a moist boundary layer present just offshore. Along the interface, which runs along the coast, isolated thunderstorms are forecast. Both, mid-level forcing but also topography play a role for initiation and hence a broad level 1 has to be introduced due to the still existent uncertainties.

The reason for the quite aggressive probability forecast is the favorable environment, which is present over those regions. Up to 25m/s DLS, 20m/s 0-3km shear, rapidly steepening lapse rates onshore and strong directional shear all indicate an augmented severe hail risk with those thunderstorms. In addition, severe downbursts are possible, given forecast depth of the dry subcloud layer. The models like GFS had a good handling in thunderstorm coverage during the past few days and therefore we will stick with a level 1 for now.

... Italy, the Balkans and extreme S-Austria ...

Weak shear and modest instability support scattered to widespread thunderstorms in a weakly capped environment. Slow storm motion enhances the flash flood risk with those storms.

Slovenia and extreme S-Austria was included into a level 1 for isolated large hail as 15m/s DLS temporarily overlaps with modest MLCAPE. Thunderstorms in all areas decay after sunset.

... NE-Europe ...

In the range of a flat trough and a diffuse surface depression, scattered thunderstorms are forecast. Shear and instability remain meager, so next to isolated large hail, no severe weather risk is forecast. The thunderstorm activity decreases after sunset.