CONVECTIVE FORECAST
VALID 12Z FRI 09/05 - 06Z SAT 10/05 2003
ISSUED: 09/05 11:57Z
FORECASTER: DAHL

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SOUTH-CENTRAL EUROPE.

GENERAL THUNDERSTORMS ARE FORECAST ACROSS CENTRAL AND SOUTHERN EUROPE.

SYNOPSIS

BROAD WSWLY UPPER FLOW WILL PERSIST OVER NORTHERN AND CENTRAL EUROPE AHEAD OF UPPER LONG-WAVE TROUGH PRESENT OVER THE NORTH ATLANTIC DURING THE PERIOD ... THIS TROUGH WILL MAKE ONLY LITTLE EASTWARD PROGRESS TODAY. WEAK UPPER CUT-OFF LOW WILL CONTINUE EAST ALONG THE COAST OF NORTHERN ALGERIA. STEEP MID-EVEL LAPSE RATES ARE COVERING EAST-CENTRAL AND SE EUROPE ... WITH RATHER VARIABLE BOUNDARY-LAYER MOISTURE ... YIELDING A WIDE RANGE OF MLCAPES WHICH COULD LOCALLY REACH 2000 J/KG /REF YESTERDAY'S 18Z PRAGUE CHECH REPUBLIC SOUNDING/. FARTHER WEST ... OVER S GERMANY ... WEAKLY UNSTABLE AND WEAKLY CAPPED AIRMASS IS PRESENT. ATTM THERE ARE NO INDICATIONS THAT AN EML WILL BE ADVECTED ATOP THE BOUNDARY LAYER ... WHICH SHOULD KEEP CAPES ON THE ORDER OF 500 TO 1000 J/KG. THOUGH PLUME OF STEEP MID-LEVEL LAPSE RATES IS BEING ADVECTED INTO THE WESTERN AND NORTHWESTERN MEDITERRANEAN REGIONS ... LOW-LEVEL MOISTURE IS QUITE MEAGER THERE AND MEAN-LAYER CAPE SHOULD GENERALLY BE QUITE MODEST. FRONTAL WAVE OVER POLAND WILL CONTINUE EAST ... AND ANOTHER WAVE HAS BEEN ANALYZED OVER CENTRAL GERMANY ... WHICH WILL ALSO CONTINUE EASTWARD DURING THE DAY.

DISCUSSION

...CENTRAL EUROPE...
FIRST TSTMS HAVE DEVELOPED ALREADY ALONG WEAK COLD FRONT OVER SOUTHWESTERN GERMANY IN WEAKLY CAPPED ENVIRONMENT. INSTABILITY SHOULD REMAIN QUITE MEAGER ACROSS MOST OF GERMANY DUE TO WEAK SURFACE HEATING. SHEAR APPEARS TO BE RATHER UNIDIRECTIONAL OR EVEN BACKING SLIGHTLY WITH HEIGHT WITH MAGNITUDES OF ABOUT 30 TO 40 KNOTS IN THE LOWEST 6 KM. THIS SUGGESTS THAT THREAT OF GUSTY WINDS AND POSSIBLY SMALL HAIL EXISTS OVER THE NEXT FEW HOURS ACROSS W AND CENTRAL GERMANY BUT ORGANIZED SEVERE STORMS ARE RATHER UNLIKELY.

HOWEVER ... AS TSTMS ARE DEVELOPING INTO SOMEWHAT WARMER AND STRONGER CAPPED AIRMASS OVER SE GERMANY ... AND AS DEEP-LAYER SHEAR INCREASES SOMEWHAT AHEAD OF A WEAK VORT MAX ATTM APPROACHING THE ALPS ... TSTMS MAY STRENGTHEN SOME. THOUGH LOW-LEVEL VEERING IS GENERALLY QUITE WEAK ... STORMS MAY PICK UP RIBBONS OF RATHER HIGH LOW-LEVEL SRH GENERATED OVER THE HILLY TERRAIN THROUGH CHANNELING AND DIFFERENTIAL DIABATIC HEATING ... AND BRIEFLY BECOME SUPERCELLULAR. IN THIS CASE ... MAIN THREAT WILL BE LARGE HAIL ... THOUGH ISOLATED SEVERE WIND GUSTS AND MAYBE A BRIEF TORNADO CANNOT BE DISCOUNTED GIVEN LOW DEW-POINT DEPRESSIONS IN THE BOUNDARY LAYER.

FARTHER EAST ... TEMPERATURES ARE CLIMBING INTO THE 30S ... WITH SURFACE DEWPOINTS AROUND 10 C ... YIELDING GENERALLY A FEW HUNDRED J/KG OF CAPE ... BUT RATHER HIGH CINH VALUES. HOWEVER ... GIVEN SOME VARIABILITY OF THE LOW-LEVEL MOISTURE ... SUBSTANTIALLY HIGHER CAPES MAY BE PRESENT LOCALLY. DEEP-LAYER SHEAR WILL INCREASE DURING THE DAY ... AND MAY BE ON THE ORDER OF 40 TO 50 KNOTS TOWARDS LATE AFTERNOON OVER EAST CENTRAL EUROPE. THOUGH PRIMARY THREAT WILL BE STRONG/DAMAGING WIND GUSTS WITH THE RATHER HIGH-BASED CELLS ... A FEW HAIL EVENTS CANNOT BE RULED OUT IF RICHER LOW-LEVEL MOISTURE IS ENCOUNTERED AND LOCALLY SUFFICIENT HELICITY IS PROVIDED.

...NORTH ITALY...
WEAK VORT MAX ... ALONG WITH UPSLOPE FLOW HAVE SUPPORTED INITIATION OVER N ITALY. INSTABILITY IS RATHER MODEST AT THE MOMENT ... BUT AS TSTMS SPREAD EAST ... THEY WILL ENCOUNTER ENVIRONMENT WHICH WILL BE SUPPORTIVE OF STRONG/DAMAGING WIND GUSTS AND LARGE HAIL AS CAPES AND DEEP-LAYER SHEAR WILL LIKELY CLIMB TO WELL ABOVE 1000 J/KG AND AROUND 40 KNOTS RESPECTIVELY. LOW LEVEL HELICITY WILL LIKELY BE ABUNDANT OVER THE PO VALLEY WHERE ELY SFC FLOW IS PRESENT. GIVEN HIGH LCL HEIGHTS ... THREAT OF TORNADOES APPEARS TO BE RATHER LOW THOUGH TOWARDS LATE EVENING ... IF POCKETS OF HIGHER BL MOISTURE ARE PRESENT IN THE PATH OF A CELL ... A BRIEF TORNADO MAY OCCUR.

OTHERWISE ... THREAT OF ORGANIZED SEVERE APPEARS TO BE RATHER LOW THIS AFTERNOON/NIGHT.

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