VALID 23Z THU 10/10 - 00Z SAT 12/10 2002
ISSUED: THU 10/10 23:12Z
FORECASTER: HAVEN

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR CNTRL AND S-ITALY, ADRIATIC SEA INTO FORMER YUGOSLAVIA

GENERAL THUNDERSTORMS ARE FORECAST OVER THE AREA SURROUNDING THE SLGT RISK AREA, WRN AND CNTRL MEDITERRANEAN SEA

SYNOPSIS

COLD AND DRY LOW LEVEL AIRMASS OVER NRN HALF OF EUROPE WILL STILL NOT BE SUPPORTIVE FOR TSTMS. FURTHER SOUTH…OVER THE CNTRL MEDITERRANEAN REGIONS, AGAIN AN ACTIVE DAY MAY COME TRUE, AS DAY-1 SPEED MAX PROPAGATES SLOWLY TO THE EAST. COLDFRONT WILL ALSO SLOWLY PROGRESS EWRD AND WILL CROSS CNTRL AND MOST OF S-ITALY, WHILE WAA IMPULSES REPEATLY MOVES OVER FORMER YUGOSLAVIA AND SURROUNDINGS.

DISCUSSION

...CNTRL AND S-ITALY, ADRIATIC SEA INTO FORMER YUGOSLAVIA...
STRONG UVM CONTINUES IVOF OF THE MENTIONED JETSTREAK AND WITH 1000-1500 J/KG AVAILABLE CAPE, IN COMBINATION WITH STRONG VERTICAL WINDHEAR, STORMS WILL BE ORGANIZED STRONG TO SEVERE WITH LARGE HAIL AND DAMAGING WINDS THE MAIN THREAT. WINDS WILL BE UNIDIRECTIONAL WITH HEIGHT, HOWEVER, SO CHANCE OF SUPERCELLS IS MORE LIMITED THAN YESTERDAY. BUT ANY RIGHTMOVING STORM MAY BE CAPABLE OF PRODUCING A TORNADO. ALSO LOW-LEVEL WINDSHEAR PROFILES MAY BE ENHANCED IN MOUNTAIN-AREAS, INCREASING THE RISK FOR SHORT-LIVED SUPERCELLULAR MODE. GREATEST THREAT OF TSTMS WILL BE NEAR COLDFRONT. THE STRONG UVM INDICATES THAT STORMS WILL LIKELY GROW INTO LARGE COMPLEXES/MCS’S.

...GREECE...
AVN MODEL CALCULATES EXTREMELY HIGH 0-3KM SRH VALUES OF 300-600 M2S-2 OVER GREECE FRIDAY MORNING, WHICH WILL SPREAD NE THEREAFTER. THIS IS DUE TO STRONG VEERING WINDS WITH HEIGHT AND TREMENDOUS SPEED SHEAR IN THE LOWEST KILOMETRES OF THE ATMOSPHERE. AS A RESULT ALSO BR SHEAR VALUES OVER 100 M2S-2 ARE CALCULATED, WELL ABOVE THE TRESHOLD FOR SUPERCELLULAR CONVECTIVE MODE. HOWEVER… LACK OF INSTABILITY WILL BE MAIN PROBLEM, WITH CAPE NEAR ZERO OR MARGINAL. BEST CHANCE FOR THE OCCURRENCE OF DEEP CONVECTION WILL BE IN COASTAL AREAS WHERE LOW LEVEL AIR IS WARMER AND MORE HUMID THAN OVER LAND AREAS AND WHERE FRICTIONAL CONVERGENCE BY A S’LY AIRFLOW ALONG THE GREECE WESTCOAST CAN SUPPORT CONVECTION. IF STORMS CAN DEVELOP IN THE MORNING…THERE IS A CONSIDERABLE RISK OF (MINI)-SUPERCELLS, DESPITE THE LOW INSTABILITY. GIVEN THE HIGH SRH VALUES …THESE STORMS COULD EASILY PRODUCE A TORNADO. ATTM THERE IS NOT ENOUGH CONFIDENCE ABOUT THIS SCENARIO, SO NO RISK HAS BEEN GIVEN, BUT AREA WILL BE MONITORED CLOSELY AND A POSSIBLE UPGRADING TO SLGT OR EVEN MOD RISK COULD BE NECESSARY.

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