CONVECTIVE FORECAST
VALID 06Z SUN 20/07 - 06Z MON 21/07 2003
ISSUED: 20/07 00:21Z
FORECASTER: GROENEMEIJER

General thunderstorms are forecast across France, the British Isles, The Benelux countries, Germany, Scandinavia, The Alps, the Balkans, the western Ukraine, Belarus the Baltic States and northern parts of western Russia.

SYNOPSIS

An upper low just northwest of Ireland will move slowly northeastward. Downstream of it a large upper ridge with weak flow is present over much of Europe. At lower levels, warm and dry air is being advected northward over western Europe which is bounded by a slow moving frontal zone on its western edge.

DISCUSSION

...Eastern and Northeastern france, Southeastern Benelux countries and much of western Germany...
The cold front on the western edge of the warm air-mass is expected to be located from the souther North Sea southward into western France at the beginning of the forecast period. At that time, a convergence line is expected to be situated over Northern France, which will likely move northward reaching a line from the north of The Netherlands into western Germany and eastern France in the afternoon. Behind the thermal low, winds will gradually back to westerly directions over France and the Benelux countries. It is not ruled out that some storms will affect northwestern France, Belgium and The Netherlands early in the day, but the most convection will likely initiate during late afternoon over eastern France and western Germany. It is not ruled out that some storms will be capable of producing marginally severe hail. A rather dry and deep boundary layer is expected in this area as temperatures will likely rise to 30 - 35 C while SFC dew points will generally be on the order of 10 - 15 C. Since the winds will be relatively weak in the environments of the storms and MLCAPE will likely not exceed a few 100s of J/kg threat of severe downdrafts seems to be quite limited. If the storm coverage becomes large and cluster into larger MCS's strong cold pools may form leading to severe wind gusts at their leading gust fronts. However, having strong doubts about this scenario, a risk category is not issued at this time.

...British Isles...
A polar air mass will be present over the British Isles during the day. A trough is forecast to be located over Ireland in the morning moving northeastward during the day and affecting much of western Great-Britain. Over land, a few 100s of J/kg of CAPE will likely become available to storms that will be present/forming at and near the trough. Based on 20-30 kt winds expected to be present at 850 hPa some rather strong gusts could occur, especially where convection becomes (linearly) organised. Gusts will however likely not reach severe levels (>=50kt).

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