CONVECTIVE FORECAST
VALID 10Z THU 30/09 - 06Z FRI 01/10 2004
ISSUED: 30/09 10:05Z
FORECASTER: GATZEN

There is a slight risk of severe thunderstorms forecast across northern Black Sea region

General thunderstorms are forecast across SE Great Britain, Benelux, eastern France, western Germany, eastern Poland, western Ukraine, western Belarus, parts of northern Mediterranean

SYNOPSIS

Upper ridge builds over northern Europe. To the SE ... a cut-off low is present over Poland. A short-wave trough rotates around this cut-off, yielding a SW-erly flow over extremely eastern Europe.

DISCUSSION

...Black Sea region ...
Warm airmass is present over the eastern Black Sea region east of a propagating cold front. Although sounding data is not available from this region ... steep lapse rates above the boundary layer are likely as indicated by soundings over 17030 Samsun and 34731 URRR to the south and east of the affected region. Surface observations show quite warm (up to 30 °C) and moist (16 °C dewpoint) low-level airmass ... and GFS CAPE forecast seem to be adequate with up to 1000 J/kg ahead of the cold front. Thunderstorms have already developed along the cold front moving NE-ward. Vertical wind shear is quite strong given NE-erly surface winds and SW-erly flow aloft. GFS forecasts show 20+ m/s deep layer wind shear and up to 10 m/s 0-1 km vertical wind shear. During the next hours ... QG forcing should remain in the range of a short-wave trough/vort-max moving NE-ward. Along the cold front ... convective activity should continue and spread southward reaching the northern Black Sea. Supercells are expected due to strong vertical wind shear capable of producing isolated large hail and damaging wind gusts. There is also a enhanced chance of tornadoes due to relatively strong low-level wind shear although LCL is not very low.

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