CONVECTIVE FORECAST - UPDATE
VALID 13Z THU 10/04 - 06Z FRI 11/04 2003
ISSUED: 10/04 12:25Z
FORECASTER: GATZEN

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN MEDITERRANEAN, GREECE

GENERAL THUNDERSTORMS ARE FORECAST ACROSS NORTHERN CENTRAL MEDITERRANEAN, ITALY, BALKANS

SYNOPSIS

STEERING LONG-WAVE TROUGH PLACED OVER CENTRAL EUROPE. STRONG WESTERLY CURRENT EXTENDING OVER SOUTHERN MEDITERRANEAN AND NORTHERN AFRICA. SHORT-WAVE TROUGH SITUATED OVER NORTHWESTERN AFRICA MIGRATES ENE-WARD. STRONG JETSTREAK AT IT'S SOUTHEASTERN FLANK WILL SPREAD INTO SOUTHERN MEDITERRANEAN.

DISCUSSION

...SOUTHERN MEDITERRANEAN, GREECE...
AT THE SOUTHEASTERN FLANK OF AFRICAN SHORT WAVE STRONG JET STREAK HAS REACHED SOUTHERN CENTRAL MEDITERRANEAN. WIND SPEED SHOULD ATTAIN 62 M/S ALONG IT'S AXIS. SYNOPTIC SCALE UVM IS FORECAST NORTH OF THIS JETSTREAK AND WILL LIKELY FOCUS ALONG THE TROUGH AXIS. DOWNSTREAM OF THIS FEATURE ... STRONG WARM AIR ADVECTION SPREADS NORTHWARD AND SHOULD REACH GREECE IN THE EVENING HOURS. RAWINSONDE DATA WITHIN ASSOCIATED WARM AIR MASS SHOW STEEP LAPSE RATES BETWEEN 850 HPA AND 500 HPA. GFS-DMO SUGGESTS MORE THAN 1000 J/KG CAPE SW OF GREECE AT FRIDAY, 00 UTC. AT THE SURFACE ... RELATIVELY WARM AIRMASS IS SITUATED OVER CENTRAL MEDITERRANEAN ... SOUTHERN ITALY ... SOUTHERN GREECE. CONVERGENCE LINE IS FORMING FROM SOUTHERN TUNESIA TO CENTRAL SICILIA. DURING THE NEXT HOURS ... THUNDERSTORMS SHOULD LIKELY DEVELOP ALONG THIS CONVERGENCE LINE AS SHORT-WAVE TROUGH APPROACHES ... AND SPREAD EASTWARD. MODERATE SOUTHEASTERLY SURFACE WINDS IN COMBINATION WITH MODERATE SOUTHWESTERLY WINDS ABOVE THE BOUNDARY LAYER SHOULD YIELD TO 30 KN VERTICAL SHEAR WITHIN THE LOWEST KILOMETER AND MORE THAN 500 M²/S² SRH. AS A RESULT, SUPERCELLS SHOULD LIKELY DEVELOP. STRONG TO SEVERE WIND GUSTS AND BIG HAIL SHOULD BE THE MAIN SEVERE THREAT ... AND PROBABLY ONE OR TWO TORNADOS / LCL IS FORCAST AROUND 700 M AGL. WITHIN THE EVENING, LINE OF CONVECTION SHOULD FORM ALONG THE CONVERGENCE LINE. MODEL OUTPUT SUGGESTS INCREASING SOUTHERLY WINDS EAST OF THIS LINE. WARM AIR MASS SHOULD SPREAD RAPIDLY NORTHWARD, AND THUNDERSTORMS WILL LIKELY SURVIVE UNTIL FRIDAY MORNING. IN ASSOCIATION WITH THIS FEATURE, SEVERE WIND GUSTS WILL BE THE MAIN SEVERE THREAT. LARGE HAIL WILL LIKELY OCCUR ... AND PROBABLY ONE OR TWO TORNADOS ACCORDING TO OROGRAPHIC ENHANCED HELICITY.

...NORTHERN CENTRAL MEDITERRANEAN, ITALY, BALKANS...
ANOTHER SHORT-WAVE TROUGH ROTATES ALONG THE EUROPEAN LONG-WAVE TROUGH, REACHING ITALY AND THE BALKANS ON THURSDAY. WARM AIR ADVECTION AND CVA SHOULD LEAD TO STRONG SYNOPTIC SCALE LIFT. SOME ELEVATED THUNDERSTORMS MAY FORM DURING THE DAY AND PROBABLY ROOT TO THE BOUNDARY LAYER. AS VERTICAL SHEAR SHOULD BE RELATIVELY HIGH, DEVELOPING THUNDERSTORMS COULD ORGANISE. HOWEVER ... THUNDERSTORM POTENTIAL IS TOO LOW TO WARRANT A SLIGHT RISK THOUGH. HEAVY RAINFALL IS EXPECTED WITHIN THE EVENING HOURS OVER CROATIA, BOSNIA-HERZEGOVNIA AND YUGOSLAVIA.

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