VALID 08Z FRI 18/10 - 06Z SAT 19/10 2002
ISSUED: 18/10 08:05Z
FORECASTER: HAVEN

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NRN ITALY INTO ERN EUROPE

GENERAL THUNDERSTORMS ARE FORECAST ACROSS THE AREA SURROUNDING THE SLIGHT RISK AREA

GENERAL THUNDERSTORMS ARE FORECAST ACROSS FRANCE

GENERAL THUNDERSTORMS ARE FORECAST ACROSS NORTH SEA, ENGLISH CHANNEL, BAY OF BISCAY AND SURROUNDING LAND AREAS

SYNOPSIS

JETSTREAM OVER NRN IBERIAN PENINSULA VIA ITALY TO POLAND IS BECOMING MORE MERIDIONAL AS COLD AIR OVER NWRN EUROPE DIGS S-SE. IN THIS FLOW A VORT MAX CAN BE FOUND AT 06Z OVER NRN-ITALY/AUSTRIA, AS INDICATED BY LATEST WV-IMAGERY, MOVING NE. UPPER TROUGH OVER NORTH SEA WILL CROSS BENELUX AND GERMANY. AT LOWER LEVELS... COLDFRONT FROM SE-POLAND OVER HUNGARY TO S-ITALY IS MOVING EAST WITH SFC TROUGH FROM SE-POLAND TO NRN ITALY AND SMALL SFC LOW NEAR TRIEST, BEHIND FRONT.

DISCUSSION

...NRN ITALY INTO ERN EUROPE...
SEVERAL AREAS WITH TSTMS ARE INDICATED BY LIGHTNING DETECTION-SYSTEM OVER ITALY AND SLOVENIA. UVM ASSOCIATED WITH APPROACHING VORT MAX AND CONVERGENCE IN SFC TROUGH WILL SUPPORT THESE TSTMS, ALTHOUGH COLD AIR ADVECTION WILL COUNTERACT VV SOMEWHAT. 00Z SOUNDING OF UDINE (LIPD) SHOWS 550 J/KG OF CAPE AND VERY STRONG 0-6 KM SHEAR OF 80 KTS. THIS WILL BE MORE THAN SUFFICIENT FOR GOOD STORM ORGANIZATION. LONG HODOGRAPH LENGHTS WILL BE SUPPORTIVE FOR DAMAGING WINDS, WHICH COULD EXCEED 60 KTS. ALSO (MARGINAL) LARGE HAIL WILL BE POSSIBLE AS WELL AS AN ISOLATED TORNADO, IF UPDRAFTS COULD DEVELOP ROTATION IN A BY OROGRAPHY MODIFIED LOW LEVEL WINDPROFILE.

...FRANCE...
DISTURBANCE OVER CNTRL FRANCE IS NOT ACCOMPANIED BY TSTM ACTIVITY ANY MORE. HOWEVER...SOME DAYTIME HEATING AND UVM DUE TO WEAK PVA WILL ADD TO DESTABILIZATION PROCESS, SO TSTMS MAY REDEVELOP IN THE AFTERNOON. MODERATE WINDSHEAR WILL SUPPORT ORGANIZATION OF STORMS INTO MULTICELLS, WHICH MAY BE ACCOMPANIED BY SMALL HAIL AND NON-SEVERE GUSTS. IN RHONE VALLEY...LOW LEVEL WINDS MAY BE MODIFIED TO A S-LY DIRECTION. UNDER A W-LY MIDLEVEL FLOW THIS WOULD ENHANCE SHEAR-VECTOR LENGHT AND SRH. SO A SUPERCELL CANNOT BE RULED OUT. UNCERTAINTY ABOUT THIS SCENARIO PRECLUDES THE ISSUE OF A SLIGHT RISK ATTM.

...NORTH SEA, ENGLISH CHANNEL, BAY OF BISCAY AND SURROUNDING LAND AREAS...
COLD AIR (BELOW -30C AT 500 HPA) IS SPREADING S. NW-LY FETCH OVER RELATIVELY WARM SEA WATERS HAS MADE CONVECTIVE MIXING DEEP ENOUGH FOR SHOWERS AND SOME TSTMS. ACTIVITY IS ENHANCED NEAR SFC TROUGH OVER NRN BENELUX AND SMALL SFC LOW NORTH OF BENELUX, MOVING SE. LOW CAPE AND LOW SHEAR PROFILES MAKE SEVERE WEATHER UNLIKELY, ALTHOUGH SMALL HAIL, GUSTS UP TO 35 KTS AND PERHAPS A WATERSPOUT MAY OCCUR.

#