Forecast Update
Valid: Fri 08 Aug 2008 09:00 to Sat 09 Aug 2008 06:00 UTC
Issued: Fri 08 Aug 2008 09:23
Forecaster: TUSCHY

SYNOPSIS

Please refer to the outlook issued at Thu 07 Aug 2008 14:53 UTC.


DISCUSSION

There are two areas of great concern regarding severe thunderstorm development:

... SW Finland ...

For the past few hours, thunderstorms developed over E-CNTRL Sweden and offshore as a dry slot overspread the warm and humid BL. Some clearing will take place over extreme S / SW Finland during the next 1-2 hours as warm front lifts northward, resulting in some diabatic heating. Forecast soundings indicate that not much heating needed for a few hundred J/kg SBCAPE release as dewpoints already are in the mid tens and the 20°C isotherm rapidly approaches from the south. Shear remains intense with strong directional and speed shear so supercells with a distinct tornado risk are possible and even a a strong tornado can't be ruled out. The risk for tornadic thunderstorms also develops further to the east later-on and hence we expanded the level-1 area eastwards.

.. N-Adriatic Sea and coastal areas...

An environment, conducive for explosive thunderstorm development develops over NE Italy and the coastal areas of the Adriatic Sea. The 00/06Z soundings of Udine already show a rapid build-up of instability and this trend will continue during the day. Dewpoints in the lower twenties and steep mid-level lapse rates should yield up to 2000 J/kg MLCAPE over NE Italy, increasing to more than 3000 J/kg just along the Adriatic Sea with MUCAPE values above 4000 J/kg possible. DLS increases from the west, increasing to 20-25m/s and thunderstorms, which will develop during the afternoon and evening hours will rapidly gain organisation. Significant hail, severe wind gusts and a few tornadoes are all possible.

We upgraded parts of the level-1 to a level-2 as enough instability/shear should be available for a large / isolated very large hail, isolated tornado and severe wind gust threat.