VALID 06Z SUN 17/11 - 06Z MON 18/11 2002
ISSUED: 17/11 00:08Z
FORECASTER: GROENEMEIJER

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE BALTIC STATES AND ADJACENT PARTS OF RUSSIA, AND PARTS OF THE SOUTHERN BALTIC SEA

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHERN, CENTRAL AND EASTERN ITALY

GENERAL THUNDERSTORMS ARE FORECAST ACROSS THE ENGLISH CHANNEL, THE BAY OF BISCAY AND THE WESTERN MEDITERRANEAN

SYNOPSIS

AN QUITE SURFACE CYCLONE NOW PRESENT OVER CENTRAL EUROPE HAS DEVELOPED TRACKING NORTHEASTWARD. IT IS SITUATED UNDER A SOUTH TO SOUTHWESTERLY JET ON THE EASTERN FLANK OF AN IMPRESSIVE UPPER TROUGH SITUATED FROM THE BRITISH ISLES TO THE WESTERN MEDITERRANEAN. A JET STREAK HAS ROUNDED THE BASE OF THE TROUGH AND WILL INDUCE NEW CYCLOGENESIS DURING THE AFTERNOON OVER THE THYRRENEAN SEA.

DISCUSSION

...THE BALTIC STATES AND ADJACENT PARTS OF RUSSIA, AND PARTS OF THE SOUTHERN BALTIC SEA...
SURFACE CYCLONE WILL DEEPEN FURTHER AND A STRONG WIND FIELD IS EXPECTED TO FORM ON ITS SOUTHERN FLANK OVER THE BALTIC SEA. A LOW-LEVEL TROUGH IS EXPECTED TO DEVELOP WITHIN THE STRONGEST PART OF THE WIND FIELD. INSTABILITY IS HIGH ENOUGH FOR SOME SHALLOW CONVECTIVE STORMS TO DEVELOP. THESE WILL LIKELY BE LINEARLY ORGANIZED ALONG OR NEAR THE TROUGH AXIS. GUSTS WILL LIKELY BE UP TO 65 KNOTS.

...SOUTHERN, CENTRAL AND EASTERN ITALY...
ON APPROACH OF UPPER VORTICITY MAXIMUM CYCLOGENESIS IS EXPECTED DURING THE AFTERNOON OVER THE THYRRENEAN SEA ALONG. CYCLONE WILL DEVELOP WITHIN FRONTAL AREA SITUATED ALONG A LINE FROM NORTHERN ALGERIA TO SOUTHERN SARDINIA TO FRIULI VENEZIA GIULIA. CYCLOGENESIS WILL CAUSE SOUTHERLY LOW-LEVEL WINDS TO THE EAST OF THE FRONTAL ZONE TO INCREASE /TO ABOUT 40 KNOTS @ 850 HPA/. IN THIS AIR-MASS MARGINAL INSTABILITY WITH SURFACE BASED LIFTED INDICES DROPPING TO AROUND -4 IS EXPECTED. PRESENT INDICATIONS ARE THAT WINDS WILL VEER ONLY SLIGHTLY WITH HEIGHT, BUT GIVEN HIGH WIND SPEEDS 0-3KM S.R.HELICITY VALUES WILL LIKELY BE IN THE 250-400 M2/S2 RANGE. LOCALLY, ESPECIALLY NEAR WESTERN COAST OF THE ITALIAN MAINLAND AND OVER THE NORTHERN ADRIATIC HELICITY WILL BE ELEVATED BY TOPOGRAPHIC EFFECTS. DURING THE MORNING CONVECTIVE ACTIVITY IN FRONTAL ZONE WILL BE ENHANCED ON APPROACH OF UPPER SYSTEM. THIS CONVECTION WILL LIKELY BE NON-SEVERE GIVEN LOW WIND SHEAR VALUES. PRESENT INDICATIONS ARE THAT DURING LATE AFTERNOON MORE CONVECTIVE ACTIVITY WILL DEVELOP NEAR AND TO THE SOUTH OF THE SURFACE CYCLONE WHERE COLD FRONT STARTS ACCELERATION EASTWARD. IT WILL LIKELY REACH THE WESTERN ITALIAN MAINLAND DURING THE EVENING AND PROGRESS EASTWARD OVERNIGHT. MAIN THREATS WILL BE SEVERE WIND GUSTS AS POTENTIAL FOR THESE IS QUITE HIGH GIVEN DRY MID-LEVELS. A SHORT LIVED TORNADO OR TWO CANNOT BE RULED OUT. SOME MARGINALLY SEVERE HAIL MAY ALSO OCCUR.

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