VALID 06Z MON 18/11 - 06Z TUE 19/11 2002
ISSUED: 18/11 00:22Z
FORECASTER: GROENEMEIJER

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL AND SOUTHERN ITALY, THE WESTERN BALKANS AND ADJACENT WATERS

GENERAL THUNDERSTORMS ARE FORECAST ACROSS THE WESTERN IBERIAN PENINSULA, THE CENTRAL MEDITTERRANEAN ARE INCLUDING THE SOUTHERN ALPINE REGION AND THE WESTERN BALKANS

SYNOPSIS

AN UPPER TROUGH IS SITUATED FROM NORTHERN FRANCE TO THE WESTERN MEDITERRANEAN. AN VORTICITY MAXIMUM NOW LOCATED OVER NORTHERN ALGERIA IS EXPECTED TO TRACK NORTHEASTWARD OVER ITALY TOWARDS THE NORTHEN BALKANS. AIR MASS OVER THE CENTRAL MEDITERRENEAN IS GENERALLY MARGINALLY UNSTABLE. A NEW TROUGH IS AMPLYFYING OVER THE EASTERN ATLANTIC AND APPROACHES THE WESTERN IBERIAN PENINSULA NEAR THE END OF THE PERIOD.

DISCUSSION

...CENTRAL AND SOUTHERN ITALY, THE WESTERN BALKANS AND ADJACENT WATERS...
A FRONTAL ZONE IS PRESENT FROM TUNESIA OVER THE WESTERN THYRRENEAN SEA TO THE NORTHERN ADRIATIC. SATELLITE AND SURFACE ANALYSIS CLEARLY SHOWS CYCLOGENESIS IS TAKING PLACE IN THE AREA. AIR-MASS IS MARGINALLY UNSTABLE WITH 50 HPA MLCAPE VALUES IN A 600 - 1200 J/KG RANGE. SURFACE BASED CONVECTION IS EXPECTED TO INITIATE AT THE BEGINNING OF THE FORECAST PERIOD ALONG THE SOUTHERN PART OF THE ZONE THAT WILL LIKELY DEVELOP INTO AN EASTWARD MOVING COLD FRONT. GIVEN STRONG WIND SHEAR BELOW 700 HPA AND LINEAR FORCING MECHANISM THE CONVECTION WILL LIKELY ORGANIZE ITSELF INTO A LINEAR MCS. STRONG WIND GUSTS WILL BE THE MAIN THREAT. SOME LOCALISED FLOODING IS POSSIBLE AS WELL AS SOME MARGINALLY SEVERE HAIL. GIVEN ONLY MODERATE LOW-LEVEL DIRECTIONAL SHEAR AND LINEAR NATURE OF CONVECTIVE SYSTEM CHANCES FOR TORNADOGENESIS ARE QUITE LOW.

...SOUTHEASTERN ALPINE REGION...
SECOND EPISODE OF HIGH PRECIPITATION HAS STARTED AT THE BEGINNING OF THE PERIOD. VERY HIGH PRECIPITATION RATES ARE EXPECTED TO CONTINUE THROUGHOUT THE PERIOD ON THE SOUTHERN SLOPES OF THE ALPS, GENERALLY EAST OF THE LUGANO AREA. THIS WILL ADD TO FLOODING PROBLEMS. OVERNIGHT PRECIPITATION SHOULD GRADUALLY CEASE.

...WESTERN IBERIAN PENINSULA...
IN THE END OF THE EVENING AN ACTIVE COLD FRONT WILL REACH WSTERN PORTUGAL. HEAVY PRECIPITATION CAN BE EXPECTED WITH THIS SYSTEM AS WELL AS SOME STRONG BUT NON-SEVERE WIND GUSTS.

#