CONVECTIVE FORECAST - UPDATE
VALID 14Z TUE 03/06 - 06Z WED 04/06 2003
ISSUED: 03/06 13:55Z
FORECASTER: DAHL

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS FRANCE...BENELUX...W GERMANY.

GENERAL THUNDERSTORMS ARE FORECAST ACROSS SOUTHERN AND CENTRAL EUROPE.

SYNOPSIS

COMPLEX PATTERN PRESENT AT LOW-LEVELS ACROSS CENTRAL EUROPE ... SHALLOW COLD FRONT IS STRETCHING ACROSS FRANCE TOWARDS THE BRITISH ISLES ... AND WILL SLOWLY CONTINUE EAST. SOUTHERLY LOW-LEVEL FLOW AHEAD OF THIS FRONT IS ADVECTING MOIST/UNSTABLE AIRMASS INTO CENTRAL AND NORTHERN PARTS OF EUROPE. SEVERAL WEAK WIND-SHIFT LINES ARE LINGERING ACROSS CENTRAL AND EASTERN GERMANY ... WHICH APPEAR TO BE ASSOCIATED WITH PLUMES OF HIGH 850 HPA THETA-E.

DISCUSSION

...GERMANY...
MODIFIED 06 Z SOUNDINGS/SFC OBSERVATIONS INDICATE ABUNDANT MOISTURE AND CAPE /LOCALLY IN EXCESS OF 1500 J/KG/ BENEATH PLUME OF ELEVATED MIXED LAYER WHICH IS LOCATED OVER CENTRAL GERMANY. FIRST TSTMS ARE DEVELOPING ALONG A WIND-SHIFT LINE AT THE EASTERN EDGE OF THE EML OVER CENTRAL GERMANY ATTM. SHEAR IS GENERALLY QUITE WEAK BUT SHOULD SLOWLY INCREASE IN THE WAKE OF THE UPPER RIDGE AXIS. EXPECT 0-3 KM SHEAR OF ABOUT 10 TO 15 KNOTS AND 0-6- KM SHEAR OF ABOUT 20 TO 30 KNOTS.

PRESENT THINKING IS THAT STORM INFLOW WILL BE FROM THE SE ... WHERE DEWPOINTS ARE ONLY ON THE ORDER OF 10 TO 13°C ... WHILE THE HIGH CAPE VALUES FARTHER TO THE WEST ARE SUPPORTED BY SFC DEWPOINTS OF 16 TO 18°C. THIS SUGGESTS THAT LCL HEIGHTS WILL BE RATHER HIGH AND THAT CAPE WILL PROBABLY REMAIN LESS THAN 1000 J/KG. THIS SUGGESTS THAT THERE IS A CHANCE OF A FEW STRONG WIND GUSTS ALONG WITH HAIL ... WHICH MAY APPROACH SEVERE LEVELS.

IF STORMS MANAGE TO INITIATE FARTHER WEST BENEATH THE EML ... AS APPARENTLY HAS HAPPENED OVER SW GERMANY ... THEY WILL HAVE BETTER CHANCES OF BECOMING SEVERE GIVEN HIGHER-CAPE ENVIRONMENT. THOUGH PRIMARY MODE SHOULD BE MULTICELLULAR ... WITH PRIMARY THREATS BEING MARGINALLY SEVERE HAIL ... STRONG WIND GUSTS AND FLASH FLOODING ... RATHER LOW LFC HEIGHTS AND LARGE CAPE DENSITIES AT LOW LEVELS WOULD PROMOTE STRONG STRETCHING AND TILTING OF HORIZONTAL HELICITY. SRH WILL GENERALLY BE RATHER LOW ... BUT INTERACTION WITH OUTFLOW BOUNDARIES/GUSTFRONTS OF NEIGHBORING STORMS ... OR OROGRAPHICALLY PERTURBED LOW-LEVEL WIND FIELD COULD YIELD SUFFICIENT SRH LOCALLY. IN THIS CASE ... A FEW ROTATING UPDRAFTS WOULD DEVELOP WITH THE THREAT OF LARGE HAIL AND A MAYBE BRIEF TORNADO OR TWO.

OVER NE GERMANY W POLAND AND THE CHECH REPUBLIC ... A FEW RATHER HIGH-BASED TSTMS SHOULD CONTINUE TO FORM. SHEAR IS MINIMAL ... AND UPDRAFTS SHOULD BE QUITE SHORT-LIVED. GUSTY WINDS AND SMALL HAIL MAY WELL OCCUR WITH THE STRONGER CELLS ... BUT SEVERE THREAT APPEARS TO BE QUITE LOW. THE SLOW-MOVING STORMS MAY LOCALLY PRODUCE LARGE AMOUNTS OF PRECIP.

...FRANCE...BENELUX...W GERMANY...
CONSIDERABLE UNCERTAINTY EXISTS WITH RESPECT TO THE DEVELOPMENT OF THE TSTMS OVER FRANCE AND THE EXPECTED DEVELOPMENT OVER W GERMANY AND BENELUX LATER TONIGHT ...

HOWEVER ... APPRECIABLE SEVERE THREAT APPEARS TO EXIST OVER N FRANCE ... W GERMANY INTO BENELUX INTO LATE TUESDAY NIGHT/EARLY WEDNESDAY MORNING. TSTMS HAVE FORMED OVER FRANCE ALONG WEAK COLD FRONT ... AND SHOULD CONTINUE EAST. MLCAPE SHOULD BE ON THE ORDER OF 1000 J/KG IN THE PREFRONTAL ENVIRON... GIVEN ABOUT 30 TO 40 KNOTS DEEP-LAYER SHEAR ... STORMS MAY ORGANIZE ALONG THE COLD FRONT/COMMON COLD POOL INTO A LINEAR MCS. ALSO ... SLY/SELY SFC WINDS ARE PRESENT AHEAD OF THE LINE ... AND POTENTIAL FOR A ROTATING UPDRAFT OR TWO EXISTS WHICH MAY PRODUCE PRIMARILY LARGE HAIL ... POTENTIAL ALSO EXISTS FOR A TORNADO GIVEN QUITE LOW LCL HEIGHTS. HOWEVER ... PRIMARY THREAT WILL BE MARGINALLY SEVERE HAIL AND DAMAGING WIND GUSTS WITH THE MAJORITY OF THE CELLS.

LATER IN THE EVENING ... LOW-LEVEL WARM ADVECTION IS EXPECTED TO INCREASE OVER W GERMANY AND BENELUX ... WHICH MAY BE ASSOCIATED WITH A DEVELOPING WAVE ALONG THE COLD FRONT WHICH CANNOT BE DIAGNOSED WITH THE DATA AVAILABLE THOUGH. HOWEVER ... DEVELOPMENT OF ONE OR MORE MCS'S ... POSSIBLY SLIGHTLY ELEVATED ... IS EXPECTED WITHIN THE WAA REGIME. STRONG WIND GUSTS ... MARGINALLY SEVERE HAIL AND LOCAL FLASH FLOODING SHOULD BE EXPECTED WITH THIS SYSTEM IF THIS SCENARIO VERIFIES.

...OTHER REGIONS ...
REF CONVECTIVE FORECAST.

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