Forecast Update
Valid: Fri 21 Aug 2009 10:00 to Sat 22 Aug 2009 06:00 UTC
Issued: Fri 21 Aug 2009 10:11
Forecaster: TUSCHY

A level 1 was issued for parts of Germany, Switzerland, parts of Austria, parts of the Czech Republic and extreme W-Poland mainly for large hail and severe wind gusts.

SYNOPSIS

Please refer to the main outlook.

DISCUSSION

... Level 1 area ...

Major changes became necessary for this outlook, downgrading and modifying most parts of the level area.

Latest model runs from GFS and WRF adapted to the ECMWF run, which was used as an outlier in the main outlook. Therefore, an ill defined prefrontal moisture and instability tongue is forecast, which limits the risk for anything severe substantially over NE/E Germany and also S-Sweden. The position of the cold front and the convergence zone were handled well with dewpoints in the mid to upper tens still present ahead of the cold front. Ongoing convection ahead of the main front limits insolation as chilly/stable airmass is present in the aftermath of overnight's convection.

Overall forecast philosophy remains the same with initiation forecast along the convergence zone over extreme west Poland and the Czech Republic but also along the cold front further west over south/central Germany. The main storm mode will be multicells with isolated supercells still possible. Overall hail and wind gust risk however precludes a level 2.

Good instability build-up is still expected over SE-Germany and extreme N-Austria, where up to 15m/s DLS and some directional shear overlap. Hail risk may be maximized over those areas, especially when more discrete cells ahead of the cold front evolve. Excessive rain becomes the dominant risk over the western Alps.