Storm Forecast
Valid: Wed 07 Sep 2011 06:00 to Thu 08 Sep 2011 06:00 UTC
Issued: Tue 06 Sep 2011 22:46
Forecaster: PUCIK

A level 1 was issued for Northeastern Germany and Poland mainly for marginally severe wind gusts and tornadoes.

SYNOPSIS

A dominant feature continues to be a significant cyclonic vortex located over Northern Atlantic with belt of strong northwesterly flow at its southern periphery, reaching locally over 60 m/s at 300 hPa level. At the forward flank of this belt, a short-wave trough will rapidly translate east-souteastwards during the day and affect much of Central Europe. Strong synoptic scale forcing is simulated with the DCVA ahead of the trough and a well developed frontal system with dry intrusion can be clearly identified in the satellite loops. The front is forecast to affect the eastern parts of Central and Northern Europe during the day. An area of high pressure lies to the south of the cyclonic vortex and more to the east, a shallow pool of low geopotentials lies over Southeastern Europe (where the highest coverage of thunderstorms is anticipated) and a stagnant low, especially prominent at mid and upper levels, is forecast over Russia.

DISCUSSION

... Northeastern Germany to Poland ...

Behind the main stratiform cloud shield, the dry intrusion over the surface front might help in the development of marginal latent instability, as suggested by many model simulations, including GFS, ECMWF and various WRF models. The degree of instability will likely stay very low, reaching at maximum few hundreds J/kg of CAPE. IPV fields suggest a strong forcing in relation to the dry intrusion and it seems that the best conditions regarding the development of very weakly electrified and strongly forced convective line will be observed over Northeastern Poland, in the exit region of the cyclonically curved jet.

Simulations are suggesting a strong westerly to northwesterly flow in association with the deep surface low, reaching 15-20 m/s at 850 hPa level and boosting up the values of low level shear, which will likely reach more than 10 m/s around the main frontal zone. The highest values of both shear and helicity should be observed in the morning hours over Eastern Germany, with diminishing trend as the day progresses. Another factor worth discussion should be low LCLs around the proposed position of convection. Current thinking is, that with a chance of low topped convective line developing in the region of dry intrusion, isolated marginally severe wind gusts or weak tornadoes can occur.