CONVECTIVE FORECAST
VALID 07Z FRI 09/07 - 06Z SAT 10/07 2004
ISSUED: 09/07 07:20Z
FORECASTER: GATZEN

There is a moderate risk of severe thunderstorms forecast across northern Balkans, Hungary, Slowakia, western Romania, southwestern Ukraine, southeastern Poland

There is a slight risk of severe thunderstorms forecast across Eastern Poland, eastern Czech Republic, southeastern Austria, northern Balkans, Adriatic, western Romania southwestern Ukraine and western Belarus

General thunderstorms are forecast across wesetrn, central and eastern Europe, central Mediterranean, northern Scandinavia and western Russia

SYNOPSIS

Intense upper long-wave trough present over the western North Sea, yielding a strong southwesterly flow over Central Europe. As it moves southeastward ... strong upper jet will spread eastward ... and should reach from southern France to the Alps and Poland on late Friday. To the east of a cold front reaching from western Poland to eastern Alpine region and further to eastern Algeria ... warm airmass has spread over southeastern Europe and central Mediterranean. This cold front will propagate southeastward on Friday ... crossing Poland, the northern Balkans and northern/central Italy.

DISCUSSION

...Eastern Poland, eastern Czech Republic, Slowakia, southeastern Austria, Hungary, northern Balkans, Adriatic, western Romania southwestern Ukraine and western Belarus ...
Focus of severe activity is expected along the cold front that has crossed Austria and northern Italy in the morning ... as strong (20+m/s) deep layer wind shear is forecast by latest model output. To the east of the cold front ... unstable airmass is present characterized by steep lapse rates reaching from 900 to 650 hPa as indicated by 00Z Vienna sounding. Rather moist boundary layer and insolation will likely produce CAPE in the order of 1500+ J/kg. During the day ... thunderstorms are likely along and to the east of the cold front. Deep layer wind shear will be sufficient for mesocyclones. Large CAPE and well-mixed mid-level airmass will enhance the chance for very large hail and severe downbursts with any supercell that forms. The chance for tornadoes will be enhanced especially over Slowakia, eastern Hungary, western Ukraine, and western Romania, where low-level wind shear is expected to increase during the day. A few tornadoes, some of them may be strong, should be possible. Convective activity may merge into one or two MCSs later on. Severe wind gusts should be the main severe threat.

...Northern France, southern Great Britain, Benelux, northern Germany, Denmark, western Poland ...
In the range of the upper trough ... maritime airmass will be slightly unstable due to insolation and moist low-level airmass. Thunderstorms are expected. Moderate low-level wind shear and deep layer wind shear over the southern portions of the affected area are forecast ... where thunderstorms may organize into small bows or multicells/mesocyclones. Marginally severe hail/wind gusts are possible, as well as a brief tornado or two. Over the southern North Sea ... weak vertical wind shear underneath the trough axis and low-level CAPE may be sufficient for water spouts during the day.

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