CONVECTIVE FORECAST
VALID 06Z SAT 19/04 - 06Z SUN 20/04 2003
ISSUED: 18/04 18:23Z
FORECASTER: DAHL

GENERAL THUNDERSTORMS ARE FORECAST ACROSS SW EUROPE.

GENERAL THUNDERSTORMS ARE FORECAST ACROSS SE EUROPA.

SYNOPSIS

UPPER BLOCK PATTERN PERSISTING ACROSS EUROPE ... WITH AN AMPLIFYING UPPER SHORT-WAVE TROUGH ATTM OVER GERMANY EXPECTED TO SPREAD WESTWARD INTO THE BRITISH ISLES AND NORTH FRANCE BY SUNDAY 06 Z ... AND CLOSE OFF INTO AN UPPER CUT-OFF LOW ON THE COURSE OF SATURDAY. SRN STREAM VORT MAXIMA WILL AFFECT IBERIA AND THE W MEDITERRANEAN AS WELL AS THE SE PARTS OF THE FORECAST AREA ON SATURDAY.

DISCUSSION

...FRANCE... SW GERMANY...
PLUME OF SUBTROPICAL AIRMASS CURRENTLY OVER THE IBERIAN PENINSULA ... IS EXPECTED TO ADVECT NORTHWARD INTO FRANCE AND PARTS OF SOUTH GERMANY. GFS CAPE FORECAST FIELDS SUGGEST DEVELOPMENT OF WEAK LATENT INSTABILITY WITHIN THIS PLUME TOWARDS THE AFTERNOON. AT THE RIM OF THE DCVA-RELATED REGION OF VERTICAL MOTION AHEAD OF THE SHORT-WAVE TROUGH ... MODELS GENERATING CONVECTIVE PRECIP ALONG THE NRN EDGE OF THE THETA-E PLUME. CURRENT THINKING IS THAT TSTMS WILL INITIATE OVER FRANCE ALONG AND S OF THE WARM-FRONTAL BOUNDARY DURING THE AFTERNOON ... ADDITIONAL TSTMS MAY FORM OVER SW GERMANY. WEAK SHEAR AND INSTABILITY SUGGEST RATHER LOW THREAT OF ORGANIZED SEVERE THUNDERSTORMS ALTHOUGH GUSTY WINDS AND SMALL HAIL WILL LIKELY OCCUR.

...SW MEDITERRANEAN...
SRN STREAM VORT MAX WILL QUICKLY SHIFT INTO THE WESTERN MEDITERRANEAN REGIONS ... THOUGH INSTABILITY OF THE WARM AIR MASS AHEAD OF THE ASSOCIATED COLD FRONT /ATTM OVER W IBERIA/ WILL BE QUITE MODEST ... STRONG UVV'S/MID-LEVEL COOLING DOWNSTREAM FROM THE DISTURBANCE SHOULD YIELD WEAK INSTABILITY IN THE PRE-FRONTAL ENVIRONMENT. VERTICAL SHEAR IS ANTICIPATED TO INCREASE SIGNIFICANTLY OVER THE W MEDITERRANEA TOWARDS LATE AFTERNOON ... AND A FEW MARGINALLY SEVERE TSTM EVENTS MAY OCCUR ... PRIMARILY WIND GUSTS WITH BOWING SEGMENTS AND MARGINALLY SEVERE HAIL. HOWEVER ... SHEAR MAGNITUDE APPEARS TO BE MARGINAL IN THE FACE OF THE MEAGER THERMODYNAMIC SUPPORT ... AND A SLGT DOES NOT APPEAR NECESSARY ATTM.

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