CONVECTIVE FORECAST
VALID 06Z SUN 17/08 - 06Z MON 18/08 2003
ISSUED: 16/08 16:19Z
FORECASTER: GROENEMEIJER

There is a slight risk of severe thunderstorms forecast across parts of France, Switzerland and Northern Italy.

General thunderstorms are forecast across parts of Russia, the Baltic States, Belarus and the extreme northern Ukrain as well as parts of the British Isles, the western mediterranean and much of west-central continental Europe.

SYNOPSIS

A ridge is located from the central Mediterranean to the North Sea. Downstream a closed low is located over northern Russia Scandinavia. Upstream... a trough is located over Iberia that will move northeastward towards central parts of Europe.

DISCUSSION

...Western continental Europe...
Upward vertical motion ahead of a vort max will likely be sustaining some (mostly) elevated convective activity over western and northwestern parts of France. These storms will be moving gradually northward possibly affecting the Benelux countries overnight. Given the low shear and low instability that will likely be in place over northern France and the anticipated elevated nature of these storms severe threat of these storms will be small.

Higher amounts of latent instability (MLCAPE50 1000 - 2000 J/kg) will likely form over much of central and southern France during the day....with the highest CAPE values likely over southern parts of France. Another area of upward motion is expected to overspread south-central France during the day and central and eastern France in the evening. As a result scattered storms are expected to form over central and south-central parts of France including the western part of the French Mediterranean coastal areas. Some other storms may affect east-central France into the evening and possibly parts of western Germany as well as the strongest forcing moves northeastward over those areas. Isolated storms may produce strong wind gusts in places as well as some large hail, but their overall will not be high. One or two MCS's may form especially where upward forcing is strongest. The chance of severe weather occurring in this area will be larger than near isolated storms and a slight risk is issued for this area.

...Northern Italy and southern Alps....
Over northern Italy, a warm and very moist boundary layer will likely still present suring the forecast period with surface temperatures in the lower 30's C and dewpoint temperatures in the low 20's inland. This will probably again lead to high MLCAPE50s of up to around 3000 J/kg like during the previous days. Weak capping and weak upslope flow will likely cause thunderstorms to form during the early afternoon over the southern Alpine slopes. Some scattered storms might also occur over the Po-Valley and near the northern Appennine mountain range. The storms will have the potential of producing large hailstones and strong wind gusts in addition to very large precipitation amounts as storms will be slow-moving and may be fixed to orographical features.

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