Storm Forecast
Valid: Wed 25 Jul 2007 06:00 to Thu 26 Jul 2007 06:00 UTC
Issued: Tue 24 Jul 2007 17:33
Forecaster: GATZEN

SYNOPSIS

Intense upper trough moves into eastern Europe during the period, while downstream subtropic ridge shifts eastward. To the west, cool air mass spreads into most of Europe except for the southwest and southeast. While weak ridge moves eastward over central Europe, another trough follows over British Isles.

DISCUSSION

Ukraine, Belarus, western Russia

Best potential for organized convection seems to exist over Ukraine area, where strong upper jet streak will be present. At low level, well-developed frontal boundary/cold front is expected to move eastwards just ahead of the region of very strong deep layer vertical wind shear. To the west, colder air mass is characterized by steep low-level lapse rates as indicated by latest soundings over Czech Rep/Slovakia. As a consequence, both air masses east and west of the frontal boundary will likely be characterized by steep lapse rates. While latest observations show that low-level moisture is rather shallow over most places, it seems that substantial moisture pooling may be possible in the range and west of the frontal boundary, where CAPE is expected by latest model output. Additionally, some moisture may also develop in front of the cold front over Ukraine, and western Russia. Current thinking is that focus of severe storms will be along the cold front. Thunderstorms will likely develop due to strong forcing. Rather weak low-level moisture and well-mixed air mass will be present, and a few strong downbursts are forecast. Given relatively strong DLS and favorable veering profiles, a few supercells capable of producing large hail are not ruled out. Thunderstorms may merge into a convective line in the afternoon moving into western Russia. Severe wind gusts are forecast be the main threat.

Further west, steep lapse rates and probably rather moist low-level air mass may be sufficient for thunderstorms in the range and east of the main trough axis. Especially ahead of this trough axis, strong deep layer vertical wind shear will be present, and thunderstorms may organize into bowing lines and multicells. Also supercells are not ruled out. Large hail and severe wind gusts are forecast to be the main threat. Thunderstorms will weaken rapidely after sunset.