CONVECTIVE FORECAST
VALID 06Z SAT 26/04 - 06Z SUN 27/04 2003
ISSUED: 25/04 19:07Z
FORECASTER: DAHL

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTHEASTERN FRANCE INTO WESTERN GERMANY.

GENERAL THUNDERSTORMS ARE FORECAST ACROSS WESTERN AND SOUTHEASTERN EUROPE.

SYNOPSIS

SHORT-WAVE TROUGH ATTM OFF THE IBERIAN ATLANTIC COAST ... WILL QUICKLY LIFT NORTHEASTWARDS ... THEREBY WEAKENING DOWNSTREAM UPPER RIDGE ... RESULTING IN BROAD/FAST ZONAL UPPER FLOW ACROSS EUROPE TOWARDS THE END OF THE FCST PERIOD. UPPER LOW NOW OVER EXTREME SE EUROPE WILL SLOWLY CONTINUE EAST AND WILL MOVE OUT OF THE FCST AREA BY SUNDAY MORNING. AT LOW LEVELS ... STRENGTHENING SWLY FLOW AHEAD OF THE VORT MAX WILL ADVECT INCREASINGLY MOIST/SLIGHTLY UNSTABLE AIRMASS NORTHWARDS.

DISCUSSION

...CENTRAL EUROPE...
PRIMARY FEATURE WILL THE LIFTING VORT MAX ... WHICH IS EXPECTED TO CROSS FRANCE ... BENELUX AND GERMANY DURING THE PERIOD. THIS FEATURE IS PROGGED TO INDUCE A FRONTAL WAVE ALONG THE COLD FRONT NOW CURVING FROM IBERIA INTO THE NORTH SEA ... WHICH WILL REACH W POLAND/W CHECH REPUBLIC BY SUNDAY 06Z. TODAY'S 12Z SOUNDINGS OF THE PRE-FRONTAL AIRMASS SHOW NEARLY MOIST-ADIABATIC/SLIGHTLY STABLE STRATIFICATION. HOWEVER ... GIVEN MID/UPPER ADIABATIC COOLING IN ADVANCE OF THE VORT MAX ... AIRMASS SHOULD BECOME MARGINALLY UNSTABLE DURING THE DAY. CONCERN WILL BE LOW-LEVEL MOISTURE WHICH WILL LIKELY BE RATHER LIMITED WITH SFC DEWOINTS IN THE 10°C RANGE. ALSO ... SUSTAINED WARM-ADVECTION AHEAD OF THE COLD FRONT SHOULD MAINTAIN MID/UPPER CLOUDINESS AND LIMIT INSOLATION. PRIND THAT MOST OF THE PRE-FRONTAL AIRMASS WILL BECOME SLIGHTLY UNSTABLE AHEAD OF THE UPPER DISTURBANCE ... WITH CAPES AT OR ABOVE 500 J/KG IF LARGER BREAKS IN THE CLOUDS OCCUR. CONVECTION SHOULD INITIATE BEFORE MIDDAY OVER WESTERN/CENTRAL FRANCE ... AND MOVE NORTHEAST ACROSS GERMANY DURING THE DAY/EVENING.

WIND FIELD WILL BE FAIRLY STRONG ... WITH 0-6 KM SHEAR MAGNITUDE ON THE ORDER OF 60+ KNOTS CLOSE TO THE VORT MAX. HODOGRAPHS SHOULD BE RATHER STRAIGHT-LINE ... AND CONVECTIVE MODE WILL LIKELY BE A LINE OF TSTMS ALONG THE FRONT ... POSSIBLY WITH BRIEF BOWING SEGMENTS/LEWPS. GREATEST SEVERE THREAT SHOULD BE DAMAGING STRAIGHT-LINE WINDS AND ISOLATED MARGINALLY SEVERE HAIL. HOWEVER ... ALLOVER SETUP APPEARS TO BE QUITE MARGINAL ... AND HAVE LITTLE CONFIDENCE ATTM THAT AN ORGANIZED LONG-LIVED SQUALL LINE WILL DEVELOP. WILL PLACE A SLIGHT RISK WHERE INSTABILITY IS EXPECTED TO BE BEST ... BUT MAY NEED TO EXPAND THE RISK AREA/UPGRADE THE RISK IF CONVECTION MANAGES TO ORGANIZE BETTER THAN CURRENTLY ANTICIPATED.

IN THE MODIFIED ... SLIGHTLY UNSTABLE POLAR AIRMASS IN THE WAKE OF THE COLD FRONT ... A FEW TSTMS MAY CROSS N FRANCE/S ENGLAND AND MOVE INTO WESTERN GERMANY LATE IN THE NIGHT BENEATH DCVA REGIME AHEAD OF H5 VORT MAX. EXPECT GUSTY WINDS AND SMALL HAIL WITH THE STRONGER CELLS.

...MEDITERRANEAN...
OTHER VORT MAX WILL CROSS THE NORTHWESTERN MEDITERRANEAN SEA ON SATURDAY ... AND REACH ITALY LATE IN THE PERIOD. LOW-LEVEL MOISTURE APPEARS TO BE RATHER MEAGER ... AND TSTMS MAY STRUGGLE TO DEVELOP. IF TSTMS CAN INITIATE THOUGH ... WIND FIELD WILL ALSO BE FAVORABLE FOR ISOLATED SEVERE WIND GUSTS AND MARGINALLY SEVERE HAIL. HOWEVER ... GIVEN WEAK LOW-LEVEL FORCING ... AND WEAK INTIABILITY ... THREAT OF ORGANIZED SEVERE APPEARS TO BE RATHER LOW ATTM.

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