Storm Forecast
Valid: Thu 02 Sep 2010 06:00 to Fri 03 Sep 2010 06:00 UTC
Issued: Wed 01 Sep 2010 19:48
Forecaster: GATZEN

A level 1 was issued for the west Mediterranean mainly for excessive rain and large hail.

A level 1 was issued for western Russia mainly for large hail.

SYNOPSIS

An amplified trough is placed over eastern Europe. Upstream, a ridge builds over western Europe. At the southern flank of this ridge, a short-wave trough moves eastward over the west Mediterranean region. Steep lapse rates and rich low-level moisture are present in the range and ahead of this trough, whereas quite stable conditions are expected over most portions of Europe due to weak low-level moisture.

DISCUSSION

West Mediterranean

Rich low-level moisture is present over the south-west Mediterranean Sea, with dewpoints in excess of 20°C. Ahead of an approaching short-wave trough, south-easterly winds are forecast to advect an elevated mixed layer northward, and latest GFS indicates MLCAPE in the order of 1000 J/kg. Underneath the trough axis, a frontal boundary is expected. To the west of this boundary, quite moist low-level air may also become unstable given the QG lift in the range of the approaching trough.

On Thursday, thunderstorms are expected to develop along the frontal boundary given the quite strong QG forcing and low-level convergence. Additional thunderstorms are forecast to develop over Sicily during the day. Storms that develop are expected to organize as the deep vertical wind shear is strong in the range of the approaching jet streak (25 m/s bulk shear in the lowest 6km). The veering profiles do also indicate a good potential of supercells. Excessive rain is forecast as well as locally large hail, severe winds, and tornadoes. The activity will likely go on in the evening and night hours as the trough moves eastward and outflow-boundaries and the sea-land-circulation will provide low-level forcing. While the deep layer vertical wind shear is expected to decrease, clustering of convection is expected with a continuing threat of excessive rain and severe winds.

Western Russia

At the eastern flank of the European trough, a strong southerly jet streak migrates over western Russia. At low levels, a frontal boundary progresses slowly eastward. In the range of this cold front, low-level dewpoints are expected to increase to 15°C, whereas quite dry low-level air is present further east. Given QG forcing, steepening lapse rates will likely result in some CAPE, and thunderstorms are forecast along the front that will move northwards. Given the weak low-level buoyancy, storms may tend to be elevated, and severe potential is reduced. Large hail and local severe wind gusts are forecast, though. Storms that root to the boundary layer will also pose a threat of tornadoes. Convective activity is forecast to weaken after sunset.