Storm Forecast
Valid: Thu 31 Aug 2006 09:00 to Fri 01 Sep 2006 06:00 UTC
Issued: Thu 31 Aug 2006 09:27
Forecaster: GATZEN

SYNOPSIS

Low geopotential present over eastern Europe ... where cool and stable airmass is present. To the west ... maritime airmass spreads northward over western Europe west of building high pressure over southerthern/central Europe.

DISCUSSION

North-western Russia

Intense upper low is centered over Belarus ... yielding a 120 kts southerly jet streak at the 300 hPa level over western Russia today ... that is forecast over north-western Russia in the evening hours. Ahead of this jet streak/short-wave ... strong DCVA is forecast by latest GFS model run. At lower levels ... warm airmass is advected northward at the eastern/north-eastern flank of the upper short-wave trough ... yielding strong QG forcing spreading northward as shown by latest model output. A warm front/occlusion is expected to move into southern Ice Sea. In the range of this frontal system ... warm airmass is present from Baltic Sea eastward ... characterized by neutral to unstable lapse rates and rich low-level moisture ... and latest ascends (Arhangelsk, Kargopol, Petrozavodsk, St. Petersburg) indicate CAPE and locally weak capping. Thunderstorms have already developed and should go on during the day due to QG forcing and low-level convergence. Given moderate vertical wind shear in the WAA regime ... with easterly surface winds and southerly upper jet ... some thunderstorms may organize ... and multicells are expected as well as a few mesocyclones in the range of locally favorable veering wind profiles. Large hail and tornadoes are not ruled out ... but most significant threat should be severe straight-line wind gusts in the range of bowing lines. In the evening hours ... increasing QG forcing is forecast as the upper vort-wax approaches ... and a MCS may form ... although models show that instability should be weak. To the south ... airmass is stable ... and thunderstorms are not expected ATTM in the range of the strong upper jet.