Storm Forecast
Valid: Fri 04 Aug 2006 06:00 to Sat 05 Aug 2006 06:00 UTC
Issued: Thu 03 Aug 2006 20:12
Forecaster: GATZEN

SYNOPSIS

Rather intense upper trough cuts off over central Europe ... while strong upper jet streak is present from western Europe to western Mediterranean and western Balkans. Another jet streak is present near the trough center from western Alps to central Italy and further to central Poland. While the southerly jet evades into central Mediterranean and eastern Balkans during the period ... northern jet streak rotates around the cut-off center reaching eastern Germany on Saturday. At lower levels ... very hot airmass has spread over southeastern Europe ... characterized by well-mixed and deep boundary-layer. To the west ... some inversions near the mean frontal boundary over eastern central Europe have lead to moist low levels. Over central Europe ... cool, moist, and well-mixed maritime airmass is present in the range of the trough's center. Further west ... low-level cold airmass is rather shallow below a strong inversion near Atlantic ridge ... while western Mediterranean cool airmass is rather unstable due to very moist boundary layer.

DISCUSSION

Southern Italy and Adriatic, central Balkans

In the range of the frontal boundary ... low level winds are expected to back east of weak surface low pressure system over central Italy. Due to quite moist boundary-layer airmass and steep lapse rates aloft ... diurnal heating should lead to significant CAPE. QG forcing underneath the jet streak should be likely ... and thunderstorms are forecast ... especially along old outflow boundaries as well as along orographic features supportig low-level convergence. Given strong DLS ... thunderstorms are expected to organize into multicells and supercells ... capable of producing large hail and severe wind gusts. Given enhanced LLS along the mean frontal boundary ... chance for tornadoes should be enhanced as well. Limiting factors will be weak CAA over a broad region as well as limited insolation due to stratiform clouds from old convective cells. However .. at least a few supercells are expected ATTM.

Western Romania, western Ukraine, Belarus, southeastern Baltic States

At the eastern flank of mean frontal boundary ... strong southerly jet has formed over eastern Europe. While the mean upper jet is present further west over Poland ... a low-level jet is expected over the affected region ... creating strong LLS as easterly surface winds are expected. Amount of instability is still questionable ... surface dew points have increased and a few thunderstorms have developed on Thursday ... but moisture may be knee-deep over most of the region. Soundings are not avialable. Current thinking is that CAPE will develop at least locally in the range of old outflow boundaries ... and thunderstorms are forecast to form along the mean frontal boundary during the day. Given strong LLS ... chance for rotating storms capable of producing large hail and tornadoes should be enhanced ... and a couple of events is forecast. Given rather weak DLS ... storms are expected to cluster later on ... with severe wind gusts along bowing lines the most significant threat. A level 2 may be warranted when low-level moisture and/or DLS will be more favorable than expected.

Germany

A few weak tornadoes/water spouts may form underneath the trough center due to weak vertical wind shear and some low-level CAPE. Over eastern/northeastern Germany ... increasing LLS is forecast west of approaching occlusion that should lead to stabilization. An overlap of significant CAPE and LLS is not expected ATTM ... however ... an update may be warranted later on.