CONVECTIVE FORECAST - UPDATE
VALID 13Z FRI 09/01 - 18Z FRI 09/01 2004
ISSUED: 09/01 13:45Z
FORECASTER: GATZEN

There is a slight risk of severe thunderstorms forecast across NERN France, Belgium, SWRN Germany, Switzerland

SYNOPSIS

Underneath the left exit region of an intense upper jet streak with an axis extending from SRN Ireland to CTRL France ... comma cloud has formed over SERN England underneath a vort-max as showed by numerical output ... moving SE-ward into France ATTM.

DISCUSSION

...NERN France, Belgium, SWRN Germany, Switzerland...
Latest satellite images show well developed comma cloud N of Paris moving SE-ward. Ahead and behind the convective system strong subsidence indicated by mostly clear sky is evident. Affected airmass is well portrayed by 12Z soundings ... indicating CAPE in the order of 100 J/kg due to convective mixing. Strong vertical wind shear and low-level veering (weak SW-erly surface winds underneath strong (50 kts) NW-erly winds @ 850 hPa in the 03882 sounding) should enhance the potential for severe thunderstorms. Shallow mesocyclones may form along the leading edge of the comma and tornadoes and hail up to 2 cm are not ruled out. Additionally ... severe wind gusts should be possible in conjunction with this system. During the next hours ... the comma should propagate SE-ward reaching the Alpine region at the end of the update period. Thunderstorms may possible over the western Alpine region and over southwestern Germany. As low level vertical wind shear should be lower in the Alpine region ... chance for severe weather should be somewhat smaller than over France.

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