Forecast Update
Valid: Fri 08 May 2009 12:00 to Sat 09 May 2009 06:00 UTC
Issued: Fri 08 May 2009 12:41
Forecaster: TUSCHY

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

SYNOPSIS

Please refer to the main outlook.

DISCUSSION

... Level-1 area ...

An update became necessary for parts of SW-Germany, Switzerland and E-France. The boundary layer yields dewpoints up to 15°C and some diabatic heating behind the departing impulse pushed surface temperatures to near or shy above 20°C. Coupled with moderate mid-level lapse rates, this is enough for up to 1000 J/kg MLCAPE release. Winds now increase from the west with 0-6km bulk shear rising to 15-20m/s, so large hail is possible, next to a few severe wind gusts.

Another upgrade was performed for parts of E-CNTRL Germany. The short-wave from the morning hours finally left the area and a few hours of insolation are likely. Dewpoints in the lower tens are enough for some moderate instability release and as shear also increases from the west, at least an isolated large hail/severe wind gust report seems possible. Latest radar scans already show numerous thunderstorms with strong reflectivity cores and also the first hail reports came in. The size of the weakly capped and unstable prefrontal sector and the broad swath of strengthening westsouthwest winds results in such an extensive level-1 area.

The level-1 for SW-France was canceled as thick cloud cover persists. Otherwise, models kept convective precipitation more isolated for the past few runs, so we don't think a level-1 would justify.

For the rest of the outlook, no major changes were performed.