CONVECTIVE FORECAST - UPDATE
VALID 17Z SAT 26/04 - 06Z SUN 27/04 2003
ISSUED: 26/04 17:03Z
FORECASTER: GROENEMEIJER

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTHEASTERN NETHERLANDS, NORTHWESTERN GERMANY AND SOUTHERN DENMARK

GENERAL THUNDERSTORMS ARE FORECAST ACROSS IRELAND, SOUTHERN BRITAIN, THE BENELUX, NORTHWESTERN GERMANY AND NORTHERN AND WESTERN FRANCE, CORSICA, SARDINIA AND CENTRAL ITALY AS WELL AS PARTS OF THE EASTERN BALKANS AND TURKEY.

SYNOPSIS

A LOW-PRESSURE AREA IS LOCATED NORTH OF IRELAND. A FRONTAL ZONE AND ASSOCIATED MID/UPPER JETSTREAM ARE POSITIONED OVER WESTERN CONTINENTAL EUROPE. A BAROCLINIC WAVE OVER THE NETHERLANDS IS MOVING TO THE NORTHEAST ALONG THE FRONT. SOUTH OF THE WAVE THE (COLD) FRONT ACCELERATES EASTWARD. A RIDGE OVER CENTRAL EUROPE WILL BE WEAKENING. DOWNSTREAM, AN UPPER TROUGH FILLED WITH COLD AIR OVER THE BLACK SEA AND CENTRAL TURKEY IS MOVING EASTWARD.

DISCUSSION

...NORTHEASTERN NETHERLANDS< NORTHWESTERN GERMANY AND SOUTHERN DENMARK...
HIGH 0-1 KM HELICITY IN BACKED LOW-LEVEL FLOW AHEAD OF COLD FRONT, AS WELL AS VERY LOW LCL HEIGHTS AND AVAILABILITY OF LOW LEVEL CAPE /PER 12Z UCCLE AND DE BILT SOUNDINGS/ HAVE PROVEN TO BE ADEQUATE FOR TORNADOGENESIS IN THE SOUTHEAST NETHERLANDS. THIS SYSTEM WILL MOVE NORTHEASTWARD AND ASSOCIATED RISK OF WEAK SHORT-LIVED TORNADOES WILL PERSIST UNTIL INSTABILITY OF THE PREFRONTAL AIR-MASS DEMINISHES DURING THE EVENING AND OVERNIGHT.

......
SOME THUNDERSTORMS HAVE DEVELOPED OVER NORTHERN FRANCE IN DESTABILSING AIR-MASS DUE TO BOTH SOLAR HEATING AND UPPER COLD ADVECTION. BECAUSE OF LOW LCL HEIGHTS AND CONSIDERABLE /20 - 25 KT/ 0-1KM SHEAR, SHORT-LIVED ROTATING UPDRAFTS CANNOT BE RULED OUT WITH THESE STORMS. IF THIS OCCURS, THERE IS A CHANCE OF SEVERE GUSTS, POSSIBLY A WEAK TORNADO AND HAIL. HOWEVER THIS CHANCE SEEMS TO BE TOO LOW TO WARRANT A CATEGORICAL RISK. THE STORMS WILL MOVE TO THE NORTHEAST, POSSIBLY AFFECTING THE SOUTHERN BENELUX THIS EVENING. THEY WILL LIKELY GRADUALLY DECAY AFTER SUNSET.

#