VALID 06Z SAT 23/11 - 06Z SUN 24/11 2002
ISSUED: 23/11 03:57Z
FORECASTER: GROENEMEIJER

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS EXTREME SOUTHEASTERN FRANCE, PARTS OF NORTHWESTERN ITALY, PARTS OF THE WESTERN MEDITERRENEAN

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS EXTREME SOUTHWESTERN IBERIAN PENINSULA.

GENERAL THUNDERSTORMS ARE FORECAST ACROSS THE ATLANTIC, PATS OF THE BRITISH ISLES, PARTS OF THE NORTH SEA, PARTS OF THE BENELUX, FRANCE, SPAIN AND AND THE IBERIAN PENINSULA AND PARTS OF ITALY AND THE WESTERN MEDITERRANEAN

SYNOPSIS

AN UPPER LOW IS LOCATED WEST OF IRELAND. A TROUGH FROM THE LOW SOUTHWARD IS EXPECTED TO AMPLIFY SOMEWHAT AND PROGRESS EASTWARD REACHING THE WESTERN IBERIAN PENINSULA BY THE END OF THE PERIOD. AIR-MASS IN A WIDE AREA AROUND THE LOW IS NEUTRAL OR SLIGHTLY UNSTABLE SO THAT WIDESPREAD CONVECTIVE OVERTURNING OCCURS. SOME CONVECTION IS LOCALLY CLUSTERED NEAR SURFACE TROUGHS. A FEW BAROCLINIC WAVES ARE EXPECTED TO FORM IN FRONTAL ZONE OVER FRANCE/IBERIAN PENINSULA/

DISCUSSION

...EXTREME SOUTHEASTERN FRANCE, PARTS OF NORTHWESTERN ITALY, PARTS OF THE WESTERN MEDITERRENEAN...
TWO BAROCLINIC WAVES ARE EXPECTED TO DEVELOP IN FRONTAL ZONE. ONE WILL DEVELOP OVER NORTHEASTERN SPAIN AND AMPLIFY ONLY SLIGHTLY. NEAR THIS WAVE FRONTAL ZONE WILL INTENSIFY AND MOVE OFF-SHORE OVER WESTERN MEDITERRENEAN. THEERE A MARGINALLY UNSTABLE AIR-MASS IS PRESENT. STRONG LOW LEVEL WINDS ARE EXPECTED TO BACK AHEAD OF COLD FRONT SOUTH OF THE ALPS. HELCITY IS THEREFORE EXPECTED TO BECOME HIGH /NEAR OR ABOVE 500 M2S-2/. CONVECTIVE ACTIVITY IS EXPECTED TO DEVELOP SOUTH OF THE ALPS DURING THE SECOND HALF OF THE PERIOD. GIVEN HIGH HELICITY ROTATING UPDRAFTS/SUPERCELLS MAY FORM. SOME LARGE HAIL AND STRONG WIND GUSTS ARE EXPECTED TO BE THE MAIN THREATS. GIVEN HIGH 0-1 SHEAR VALUES AND LOW LCL HEIGHT A TORNADO OR TWO MAY BE ALSO BE POSSIBLE.

...EXTREME SOUTHWESTERN IBERIAN PENINSULA...
NUMERICAL MODELS AGREE ON DEVELOPING A SECOND MORE AMPLIEFYING BAROCLINIC WAVES JUST WEST OF SOUTHERN PORTUGAL. THAT WAVE IS EXPECTED TO BE LOCATED OVER THE SOUTHWESTERN IBERIAN PENINSULA AT THE END OF THE PERIOD. A STRONG WIND FIELD IS EXPECTED TO DEVELOP ALONG ITS SOUTHERN FLANK. GIVEN SLIGHTLY UNSTABLE AND UNCAPPED ATMOSPHERE WIDESPREAD CONVECTIVE ACTIVITY IS EXPECTED TO OCCUR INV OF THE WAVE. DEVELOPMENT OF A LINEAR MCS ALONG COLD FRONT ASSOCIATED WITH THE WAVE SEEMS LIKELY. GIVEN STRONG /NEARLY UNIDIRECTIONAL/ SHEAR VALUES STRONG GUSTS WILL BE THE MAIN THREAT. SOME SMALL HAIL IS ALSO POSSIBLE. SOME STORMS WITH MARGINALLY SEVERE GUSTS MAY OCCUR BEHIND THE COLD FRONT.

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