CONVECTIVE FORECAST
VALID 06Z TUE 17/06 - 06Z WED 18/06 2003
ISSUED: 16/06 21:13Z
FORECASTER: DAHL

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTHERN FRANCE ... S BELGIUM ... EXTREME WEST-CENTRAL GERMANY.

GENERAL THUNDERSTORMS ARE FORECAST ACROSS THE MEDITERRANEAN ... SW AND SE EUROPE.

GENERAL THUNDERSTORMS ARE FORECAST ACROSS PORTIONS OF W RUSSIA.

SYNOPSIS

MEANDERING UPPER WLY FLOW EXTENDING ACROSS EUROPE ... WITH A DE-AMPLIFYING SHORT-WAVE RIDGE EXPECTED TO CROSS CENTRAL EUROPE DURING TUESDAY. ADJACENT SHORT-WAVE TROUGH ATTM OVER THE E ATLANTIC ... IS PROGGED TO PROGRESS EASTWARD AND TO STRETCH FROM N ENGLAND INTO S IBERIA TOWARDS TUESDAY AFTERNOON. WEAK SOUTHERN-STREAM VORT MAXIMA WILL CONTINUE TO AFFECT THE MEDITERRANEAN REGIONS. AT LOW LEVELS ... WEAKLY TO MODERATELY UNSTABLE SUBTROPICAL AIRMASS IS RESIDING OVER SPAIN ... FRANCE ... THE MEDITERRANEAN ... INTO THE WESTERN AND SOUTHERN BALKAN STATES. AIRMASS ATTM OVER FRANCE WILL BE ADVECTED INTO BELGIUM ... W AND S GERMANY AHEAD OF THE APPROACHING SHORT-WAVE TROUGH/COLD FRONT. IN THE WAKE OF THIS FRONT ... HIGH PRESSURE WILL SPREAD INTO THE WESTERN PARTS OF CENTRAL EUROPE.

DISCUSSION

...FRANCE ... S BELGIUM ... EXTREME W GERMANY...
TSTMS ARE EXPECTED TO INITIATE ALONG THE COLD FRONT TOWARDS EARLY AFTERNOON OVER CENTRAL FRANCE AS DCVA ASSOCIATED WITH THE APPROACHING SHORT-WAVE TROUGH OVERSPREADS THE REGION. 12Z SOUNDINGS ... BOLAM'S 850 HPA THETA-E FIELDS ALONG WITH LATEST SFC OBSERVATIONS SUGGEST THAT PLUME OF QUITE MOIST AIRMASS IS PRESENT OVER SW FRANCE ATTM ... LOW-LEVEL DEWPOINTS IN THE 18 TO 20°C RANGE ALONG WITH AFTERNOON TEMPERATURES IN THE UPPER 20'S ... HAVE RESULTED IN 1500 TO 2000 J/KG MLCAPE THIS AFTERNOON ... AIDED BY STEEP LAPSE RATES OF ABOUT 8 K/KM ABOVE THE BOUNDARY LAYER. MODEL FIELDS INDICATE THAT 850 HPA THETA-E PLUME WILL HAVE WEAKENED SOME BY TUESDAY AFTERNOON ... AND SOMEWHAT LOWER CAPE'S THAN TODAY MAY BE COMMON OVER FRANCE TOMORROW. HOWEVER ... SHEAR IS EXPECTED TO INCREASE WITH THE ADVENT OF THE TROUGH ... AND 30 TO 40 KNOTS DEEP-LAYER SHEAR MAY BE IN PLACE IN THE AFTERNOON/EVENING. THOUGH LOW-LEVEL HELICITY WILL LIKELY BE VERY LOW OWING TO WEAK LOW-LEVEL FLOW ... FLOW PERTURBATIONS CAUSED BY OUTFLOW BOUNDARIES OR OROGRAPHIC FEATURES MAY LOCALLY SUPPORT SUFFICIENT SRH FOR SUPERCELLS TO FORM. THESE SUPERCELLS ... IF THEY HAPPEN TO FORM INDEED ... SHOULD BE VERY ISOLATED AND RATHER SHORT-LIVED. HOWEVER ... QUITE LOW LCL HEIGHTS ARE EXPECTED ... AND PRODUCTION OF LOW-LEVEL ROTATION HAS SHOWN TO BE QUITE EFFECTIVE THEN ... SUGGESTING THAT A SOMEWHAT ENHANCED PROBABILITY FOR A TORNADO OR TWO EXISTS. ALSO ... DAMAGING WIND GUSTS AND VERY LARGE HAIL MAY ACCOMPANY ANY SUPERCELL THAT FORMS. HOWEVER ... THE MAJORITY OF THE STORMS SHOULD BE OF NON-SUPERCELLULAR NATURE. RATHER DRY MID-LEVELS AND STRONG CAPE ALONG WITH MARGINAL DEEP-LAYER SHEAR WILL PROMOTE STRONG OUTFLOW WINDS ALONG WITH SOME HAIL THOUGH ... MAYBE BRIEFLY APPROACHING SEVERE LEVELS. WILL PLACE A SLGT RISK OVER NORTHERN PORTIONS OF FRANCE ... S BELGIUM AND EXTREME W GERMANY WHERE SHEAR IS EXPECTED TO BE STRONGEST.

THE TSTMS SHOULD EVOLVE INTO A LINEAR MCS LATE IN THE DAY WHICH MAY SURVIVE WELL INTO THE NIGHT.

...IBERIA...
AHEAD OF THE TROUGH ... HIGH-BASED TSTMS ARE EXPECTED TO DEVELOP OVER THE IBERIAN PENINSULA. AS TYPICAL FOR THIS REGION ... CAPE VALUES WILL GENERALLY BE NOT VERY IMPRESSIVE ... BUT DEEP DRY SUBCLOUD LAYER INDICATES THAT A FEW DAMAGING WIND GUSTS WILL BE POSSIBLE ... ESPECIALLY IF STORMS EVOLVE INTO ONE OR MORE MCS'S ... ALLOWING STRONG COLD POOLS TO FORM LATE IN THE DAY. ALLOVER COVERAGE OF SEVERE WIND EVENTS IS EXPECTED TO BE RATHER LOW THOUGH OWING TO VERY WEAK DEEP-LAYER SHEAR AND A SLGT IS NOT WARRANTED ATTM.

...ITALY ... GREECE...
ANOTHER ROUND OF TSTMS IS EXPECTED OVER ITALY ... GREECE AND THE WESTERN BALKAN STATES. SHEAR WILL BE MINIMAL ... BUT SMALL PROBABILITIES EXIST FOR MESOCYCLONES AS LOCALLY 0-3 SRH IS EXPECTED TO BE ENHANCED BY EITHER OUTFLOW BOUNDARIES OR LOW-LEVEL FLOW MODIFICATIONS OVER THE COMPLEX TERRAIN. MAIN THREAT WILL BE LARGE HAIL WITH ANY ROTATING STORM THAT FORMS ... AND MAYBE A BRIEF TORNADO. HOWEVER ... VERY LOW BACK-GROUND SRH ALONG WITH VERY WEAK DEEP-LAYER SHEAR IS LIMITING CHANCE OF ORGANIZED SEVERE STORMS.

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