VALID 00Z FRI 01/11 - 00Z SAT 02/11 2002
ISSUED: 31/10 00:40Z
FORECASTER: HAVEN

GENERAL THUNDERSTORMS ARE FORECAST ACROSS WESTERN AND CENTRAL MEDITERRANEAN SEA

GENERAL THUNDERSTORMS ARE FORECAST ACROSS SOUTHERN BRITISH ISLES, NORTHWEST FRANCE, BENELUX

SYNOPSIS

POSITIVELY TILTED UPPER TROUGH FROM SE-FRANCE TO BALEARIC ISLANDS IS BECOMING AN UPPER LEVEL LOW AND WILL MOVE TOWARDS TUNESIA. STRONG ZONAL UPPER FLOW OVER CNTRL NORTH-ATLANTIC IS PROGRESSING TOWARDS EUROPEAN CONTINENT, WITH UPPER TROUGH REACHING U.K. FRIDAY EVENING.

DISCUSSION

...WESTERN AND CENTRAL MEDITERRANEAN SEA...
COLD AIR (T500 ARND -19C) NEAR FORMING UPPER LOW OVER RELATIVELY HIGH SST OF 21C WILL CREATE UNSTABLE PROFILES, WITH SBCAPE IN THE ORDER OF 1000-1500 J/KG. SHEARPROFILES ARE TOO WEAK TO SUPPORT ORGAINZED STORMS, HOWEVER. NEAR SFC LOW/TROUGH... WHERE LOW WIND, LOW WINDSHEAR AND ENHANCED CONVERGENCE CREATE A FAVOURABLE ENVIRONMENT FOR VORTEX-STRETCHING... A FEW WATERSPOUTS MIGHT OCCUR. THEREFORE A SEE TEXT IS GIVEN.

...SOUTHERN BRITISH ISLES, NORTHWEST FRANCE, BENELUX...
STRONG UVM ARE CALCULATED BY MODELS AS APPROACHING UPPER TROUGH BECOMES MORE NEGATIVELY TILTED. ALTHOUGH ELEVATED CONVECTION CANNOT BE RULED OUT BY LOOKING AT PROGSOUNDINGS, FOCUS IS ON THE COLDFRONT OCCLUSION WHERE STRONG UVM ARE CALCULATED, WHICH WILL REACH BENELUX EARLY ON SATURDAY. DESPITE THE MARGINAL TO LOW CAPE /BELOW 250 J/KG/ , 0-6 KM SHEAR OF 50 KTS WILL BE SUFFICIENT FOR GOOD STORM ORGANIZATION, WITH WINDGUSTS BETWEEN 40 AND 50 KTS QUITE POSSIBLE. ALSO AN ISOLATED TORNADO CANNOT BE RULED OUT, SINCE 0-3 KM SRH WILL BE BETWEEN 150 AND 300 M2S-2, THEREBY FAVORING UPRDRAFT ROTATION. BUT ATTM OVERALL SEVERE THREAT SEEMS TOO LOW TO WARRANT A SLGT RISK.

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