Storm Forecast
Valid: Wed 12 Mar 2008 06:00 to Thu 13 Mar 2008 06:00 UTC
Issued: Tue 11 Mar 2008 21:41
Forecaster: GATZEN

SYNOPSIS

An intense trough is situated over northern Atlantic extending into the North Sea. A strong upper westerly jet stream is present at its southern flank to the north of a subtropical ridge over south-western Europe. To the east of the delta of this jet stream, a sharp and amplified upper trough moves rapidly into east Europe, affecting the Aegean Sea during the period. At lower levels, a surface low pressure system is centred over the North Sea. At its southern flank, a surface low pressure trough is forecast to move eastward associated with high winds from British Isles to northern France, Benelux, and northern Germany. Ahead of this trough, cyclogenesis is expected along a frontal boundary now present over northern France. The cold front will cross central Europe quickly during the period.

DISCUSSION

Southern Germany, Austria

Main focus of severe weather is expected along the cold front that will cross southern Germany in the morning hours. Latest ascends over France indicate that very moist low-level air mass is present within the warm sector with dew points around 8°C from southern Germany to Austria. Warm air mass is expected to be moist neutral initially, but latest GF model run indicates that a mid-level trough amplifies underneath the cyclonic flank of the upper jet streak that is forecast to travel south-eastward into Alpine region. While the surface cold front is forecast to slow-down over southern Germany, the upper trough may spread into the warm sector air mass, leading to QG forcing and steeper mid-level lapse rates. Latest GFS model run indicates some CAPE forming along the cold front. However, great uncertainty exists about the development of pre-frontal instability as latest models show a rather complex upper flow regime. DCVA fields do not look very impressive, and main QG forcing may be shifted to the north into Czech Rep. and southern Poland.

Current thinking is that a strongly forced convective line accompanied by strong rain and small hail will develop. It will likely move across southern Germany, affecting most of Austria during the day. Although there are big uncertainties about the development of a cold pool, it seems that severe wind gusts will pose a significant threat along the convective line. Along the leading gust front, tornadoes are also forecast given 300 J/kg 0-1 km SRH and rather high low-level buoyancy.

Northern France, Alps, Czech Republic, eastern Germany, Poland, Slovakia, Hungary, eastern Romania, northern Serbia to northern Adriatic

Along the cold front/cold front occlusion, very moist air mass may destabilize in the range of the propagating jet streak/upper trough. Latest indications show that there is the potential for a convective line that will move into the region during the period. Along the leading gust front, moderate to high vertical wind shear and high low-level SRH are forecast by latest models. Although some severe wind gusts are supposed to be the main threat, a few tornadoes are not ruled out.

Turkey

In the range of the propagating trough, moist low-level air mass will likely destabilize due to steep mid-level lapse rates and some QG forcing. Given some low-level convergence, expect that thunderstorms will develop. As vertical wind shear will be weak, a threat of waterspouts especially along the Turkish coast is forecast during the period.