CONVECTIVE FORECAST - UPDATE
VALID 16Z SUN 27/07 - 06Z MON 28/07 2003
ISSUED: 27/07 16:30Z
FORECASTER: GROENEMEIJER

There is a moderate risk of severe thunderstorms forecast across eastern Germany, the western Czech Republic and western Poland

There is a moderate risk of severe thunderstorms forecast across the lower Rhone valley, much of the French mediterranean coastal area

There is a slight risk of severe thunderstorms forecast across an area surrounding the moderate risk areas including much of Germany, eastern France, the Alps, western Poland, the Czech republic and southeastern Sweden

General thunderstorms are forecast across much of western continental Europe, southern and central Scandinavia and parts of eastern Europe and northern Turkey

SYNOPSIS

An upper trough over the eastern Atlantic is gradually moving eastward into Europe. Downstream...a strong theta-e advection regime is in place over eastern France and central Europe. A wavy cold front over France is moving eastward.

DISCUSSION

...the lower Rhone valley, the French Mediterranean coastal area...
Strong latent instability is in place over southeastern France per 12 Z Nimes sounding, which shows about 2400 J/kg MLCAPE50 is available in the area. Winds along the coast have a tendency to remain easterly at the coast and southeasterly in the lower Rhone Valley, while winds at the top of the boundary layer are westerly and become increasingly stronger. This implies low level shear will strengthen during the next few hours. In combination with low LCL heights this implies that there is a chance of a few tornadoes that could be strong (> F1).

...eastern Germany, Poland, Czech Republic, Austria...
Storms have formed over eastern and southeastern Germany. Although shear profiles are somewhat stronger to the west, shear should be adequate for rotating updrafts/supercells. At the moment, discrete storms are clustering quite rapidly into one or more linear convective systems that will likely develop bowing segments. Given that a deep, warm and dry boundary layer is present near the storms, strong evaporational cooling will likely lead to widespread damaging wind gusts, especially as large-scale cold pool formation occurs with mesoscale convective systems. Large hail will likely also occur. Over Austria some storms with wind large threat may also develop, but the storms coverage will likely be lower. Later in the evening...widespread convective activity will likely still be ongoing over northeastern parts of Germany, the Czech Republic and Poland. Low-level shear profiles are forecast to have increased quite significantly ocer that area, so that in combination with lowered LCL heights a threat of isolated tornadoes develops.

...Sweden...
It seems likely that the wave and the associated convective activity will be located near southeastern Sweden at the end of the forecast period and that some 100s of J/kg CAPE will be available in its warm sector. Strong low-level shear seems likely so that storms will be capable of producing strong gusts and pose a threat of a weak tornado and some large hail as well.

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