Forecast Update
Valid: Sat 19 Apr 2008 13:00 to Sun 20 Apr 2008 06:00 UTC
Issued: Sat 19 Apr 2008 13:06
Forecaster: GROENEMEIJER/TUSCHY

SYNOPSIS

Please refer to the outlook issued at Fri 18 Apr 2008 21:50Z .

DISCUSSION

...Pannonian Plain...

As the boundary layer warms in response to insolation, CAPE on the order of 500-1000 J/kg is developing over much of the Pannonian Plain in the wake of a partly convective precipitation zone currently over E Hungary into Transsylvania.

Visible imagery and radar indicates that towering cumulus are developing into storms over eastern Austria, Slovenia and northern Croatia. Strong, 20-25 m/s, 0-6 km shear should suffice for rapid storm organization including supercells and linear convective elements. The storms are expected to move eastward during the afternoon and will be capable of producing some large 2-4 cm hail and strong gusts. A few tornadoes are possible as well given strong (10-15 m/s 0-1 km) low-level shear, including an isolated strong (F2 ) tornado. Gradually, storms will likely cluster and become more linearly organized.

Compared with the initial forecast, the threat has been shifted a little bit southward over Slovakia as abundant cloudiness will likely prevent surface-based initiation except in southern parts. The threat has been extended a bit further to the southeast also, as any isolated storm developing in SW Romania or central/eastern Serbia will be able to profit from very strong shear.

... Parts of NW Ukraine and SE Belarus ...

Latest VIS images reveal some clearing and increasing convective activity over N-Ukraine and this trend should continue during the next few hours. LL shear is enhanced and as LCL stays low there exists the risk of an isolated tornado report. Thunderstorms will diminish in number and intensity after sunset.

... SE France ...

Latest model trends indicate that main thunderstorm activity will occur after 06 UTC. Isolated activity before this time will profit from 25m/s of deep-layer shear, but weak instability should not yet be high enough to support strong updrafts.