CONVECTIVE FORECAST
VALID 12Z WED 30/04 - 06Z THU 01/05 2003
ISSUED: 30/04 10:56Z
FORECASTER: DAHL

THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS POLAND.

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL AND WESTERN EUROPE.

GENERAL THUNDERSTORMS ARE FORECAST ACROSS CENTRAL EUROPE AND THE N MEDITERRANEAN.

SYNOPSIS

VERY IMPRESSIVE UPPER LONG-WAVE TROUGH PRESENT OVER THE EATSREN ATLANTIC ... WITH EMBEDDED VORT MAX ATTM OVER THE IBERIAN PENINSULA EXPECTED TO LIFT NORTHEASTWARDS RAPIDLY AT THE WESTERN PERIPHERY OF THE MAIN TROUGH. AT LOW LEVELS ...THETA-E ADVETION INTO CENTRAL EUROPE IS CONTINUING WITH THE SLY FLOW AHEAD OF THE TROUGH. MAIN FRONTAL BOUNDARY IS CURVONG ACROSS FRANCE AND CENTRAL GERMANY INTO EASTERN POLAND. SLY SFC FLOW WILL BE AUGMENTED WITH CYCLOGENESIS ONGOING OVER FRANCE AHEAD OF THE IBERIAN VORT MAX. DEVELOPING LOW IS EXPECTED TO DEEPEN RAPIDLY AND SHIFT INTO THE BALTIC SEA TOWARDS THE END OF THE PERIOD.

DISCUSSION

...POLAND...
MAIN QUESTION TODAY WILL BE WHETHER/WHERE LARGE GAPS WILL OCCUR IN EXTENSIVE MID/UPPER CLOUD SHIELD SPREADING ACROSS MUCH OF CENTRAL EUROPE. 00Z SOUNDINGS OF THE WARM-SECTOR AIRMASS OVER S GERMANY AND THE CHECH REPUBLIC INDICATE STEEP MIDLEVEL LAPSE RATES ... APPARENTLY ASSOCIATED WITH AN ELEVATED MIXED LAYER. MODIFIED SOUNDINGS SUGGEST THAT SURFACE PARCELS MAY ACQUIRE CAPES ON THE ORDER OF 500 TO 1000 J/KG WHERE CLOUDS DON'T INHIBIT INSOLATION.

WARM ADVECTION IS MAINTAINING FIELDS OF MID-LEVEL CONVECTION/WEAK ELEVATED THUNDERSTORMS ACROSS S GERMANY ... WHICH SHOULD CONTINUE TO SPREAD NORTH OVER THE NEXT HOURS ... THEREBY CONTAMINATING THE PREFRONTAL ENVIRONMENT.

KINEMATIC PROFILES WILL BE MORE THAN ADEQUATE FOR ORGANIZED SEVERE STORMS ... WITH 300 HPA JET OF AROUND 150 KT AND 500 HPA FLOW OF 80 TO 100 KTS. AHEAD OF THE COLD FRONT ...LOW-LEVEL WARM ADVECTION AND ISALLOBARIC WINDS SHOULD RESULT IN SUBSTANTIAL VEERING OVER NE GERMANY AND N POLAND. NORTH OF THE WARM-FRONTAL BOUNDARY EXPECTED OVER THE S BALTIC SEA LATE THIS AFTERNOON ... LOW-LEVEL VEERING WILL BE MAXIMIZED.

PRESENT THINKING IS THAT PRECIP ASSOCIATED WITH MIDLEVEL CLOUDS WILL OBSTRUCT DEVELOPMENT OF SURFACE-BASED CAPE ACROSS MOST OF GERMANY ... AND THAT BEST CHANCES FOR SURFACE-BASED CONVECTION WILL EXIST OVER CENTRAL AND NORTHERN POLAND WHERE SKIES SHOULD REMAIN FAIR THROUGH MOST OF THE DAY ... AND WHERE LOW LEVEL WIND FIELDS WILL BE MAXIMIZED GIVEN EXPECTED RAPID DEEPENING OF THE LOW.

IF THUNDERSTORMS MANAGE TO FORM ... POTENTIAL EXISTS FOR ORGANIZED SEVERE TSTMS WITH THE MAIN THREAT BEING WIDESPREAD DAMAGING WINDS ALONG THE COLD FRONT. CLOSER TO THE LOW CENTER ALONG THE WARM FRONT ... AHEAD OF THE COLD FRONT ... AND IN THE FIRST HOURS AFTER INITIATION ... SUPERCELLULAR STORMS ARE POSSIBLE ... WHICH WOULD POSE THE THREAT OF LARGE HAIL ... WIND DAMAGE AND TORNADOES.

STORMS SHOULD INITIATE ALONG THE COLD FRONT DURING THE AFTERNOON OVER ERN GERMANY/WRN POLAND AND MAY DEVELOP INTO A LEWPY SQUALL LINE. GIVEN VERY STRONG WIND PROFILES ... ISOLATED SIGNIFICANT SEVERE THUNDERSTORMS MAY OCCUR, ESPECIALLY WITH REGARDS TO DAMAGING WIND SPEEDS.

...CENTRAL AND WESTERN EUROPE...
DEEP POSTFRONTAL CONVECTION IS EXPECTED AHEAD OF ANOTHER VORT MAX RUNNING IN FROM THE WEST ... AND NEAR THE THERMAL-TROUGH AXIS OF THE MAIN TROUGH. GIVEN STRONG SHEAR ... POTENTIAL FOR BRIEF BOW ECHOES AND MESOCYCLONES WILL EXIST ... WITH PRIMARY THREAT BEING SEVERE WIND GUSTS. ANY ROTATING STORM WILL POSE THE THREAT OF LARGE HAIL AND ISOLATED TORNADOES.

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