Storm Forecast
Valid: Thu 07 Sep 2006 06:00 to Fri 08 Sep 2006 06:00 UTC
Issued: Thu 07 Sep 2006 04:46
Forecaster: GATZEN

SYNOPSIS

High builds over British Isles, yielding CAA over Scandinavia and Germany today ... and Scandinavian trough evades into central Europe. To the south ... rather warm and unstable air mass is present from Iberian Peninsula to Alpine region and further to Poland in the range of relatively high geopotential. Weak upper trough is present over western Mediterranean.

DISCUSSION

Northern Poland

Some potential for organized convection seems to exist along an intense cold front moving SEward over France, Germany, and Poland. While shallow cold airmass spreads southward rather quickly over Germany and France ... latest model output suggests that frontal boundary will be rather slow over Poland ... yielding WAA and southerly surface winds during the day. As a consequence ... stronger QG forcing is possible along and east of the cold front ... and vertical wind shear should be rather strong. Expect that thunderstorms will form along the cold front ... low-level convergence and vertical wind shear should lead to longer living, organized thunderstorms that move south-eastward during the evening. Limiting factor will be lack of insolation due to mid-level clouds in the WAA regime ... but given moist low-level air mass and steep mid-level lapse rates to the south-west ... latest GFS CAPE calculations seem to be reasonable. Along the cold front ... strong wind gusts should be the main severe threat. Embedded mesocyclones may form due to favorable low-level helicity ... capable of producing isolated large hail ... and tornadoes are not ruled out ... especially in the evening hours, when low-level vertical wind shear is expected to increase. Rapidely low-level stabilization after sunset should cause weakening of the storms.

Germany, France

The south-western part of the cold front should be dominated by low-level CAA as indiacted by latest model output. Expect that long-living storms will not form as QG forcing and storm inflow will be not favorable. Although DLS will be in the 20 m/s range over northern Germany in the afternoon hours, severe storms should be quite unlikely ... and expect non-severe stormy gusts along the cold front. Over south-western Germany/eastern France ... latest profiles indicate stronger instability ... and CAPE in the order of 1000 J/kg is likely. Thunderstorms that form near the cold front will have a potantial to organize as vertical wind shear slightly increases. However ... expected wind profiles should be not that impressive .. with 15 m/s DLS expected ... and chance for large hail and severe wind gusts should be only slightly enhanced compared to convection developing further south. A level 1 seem to be not warranted ATTM.