VALID 07Z SUN 24/11 - 06Z MON 25/11 2002
ISSUED: 24/11 07:47Z
FORECASTER: GROENEMEIJER

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS SOUTHEASTERN FRANCE, NORTHERN ITALY AND THE WESTERN MEDITERRANEAN SEA

GENERAL THUNDERSTORMS ARE FORECAST ACROSS PARTS OF WESTERN AND SOUTHWESTERN EUROPE

SYNOPSIS

AN UPPER-LEVEL LONGWAVE TROUGH IS PRESENT FROM THE BRITISH ISLES TO THE WESTERN IBERIAN PENINSULA. THE TROUGH IS EXPECTED TO PROGRESS SLIGHTLY TO THE EAST DURING THE PERIOD. AN INTENSE SHORTWAVE TROUGH IS VISIBLE ON WV IMAGERY OVER THE SOUTHERN IBERIAN PENINSULA. THIS TROUGH WILL BE LOCATED OVER SOUTHEASTERN FRANCE AT THE END OF THE PERIOD. THE AIR-MASS IS MARGINALLY UNSTABLE OVER AND INV OF THE ATLANTIC AND MEDITERRANEAN WATERS.

DISCUSSION

...SOUTHEASTERN FRANCE AND NORTHWESTERN ITALY...
AN INTENSE SHORTWAVE OVER SOUTHERN SPAIN HAS LEAD TO FORMATION OF A LINEAR MCS OVER THE MEDITERRANEAN WATERS SOUTH OF ANDALUCIA. THOUGH NO SEVERE GUSTS HAVE BEEN REPORTED, PROBABILITIES OF SEVERE WEATHER OCCURRING WITH THIS SYSTEM WILL LIKELY INCREASE AS LOW-LEVEL WIND SHEAR IS EXPECTED TO INCREASE IN RESPONSE TO THE FORMATION OF A MID-LEVEL /700 HPA/ 50 KT-JET-STREAK. A WEAKER VORT MAX AHEAD OF AFOREMENTIONED SHORTWAVE IS PRESENT EAST OF SPAIN. THIS VORT MAX WILL INTENSIFY AS THE MID-LEVEL JET STRENGTHENS. WITHIN THE LEFT PART OF THE MID-LEVEL JET EXIT REGION SURFACE CYCLOGENESIS WILL TAKE PLACE NEAR THE BALEARES. THIS WILL LEAD TO BACKING LOW LEVEL WINDS IN THE NORTHERN PART OF THE RISK AREA CREATING HIGH S.R.HELICITY VALUES /AROUND 300 TO 500 M2S-2 IN PLACES/. IN ADDITION TO CONVECTION NEAR SURFACE CYCLONE CORE...NEW CONVECTIVE ACTIVITY IS EXPECTED TO INITIATE SOUTH OF THE CORE /ALONG COLD FRONT/ TRACKING NORTHEASTWARD AND AFFECTING SOUTHEASTERN FRANCE AND NORTHWESTERN ITALY LATER THIS EVENING AND OVERNIGHT. WITHIN THIS CONVECTION A FEW ROTATING UPDRAFTS /EMBEDDED SUPERCELLS/ MAY FORM YIELDING A PROBABILITY OF SEVERE WIND GUSTS, TORNADOES AND LARGE HAIL. INSTABILITY WILL BE A LIMITING FACTOR HOWEVER AS MLCAPE IS NOT EXPECTED TO EXCEED 800 J/KG.

...ALPINE REGION...
GRADIENT OVER ALPINE RANGE IS EXPECTED TO INCREASE OVERNIGHT. ON THE SOUTHERN SLOPES STRONG UPSLOPE WINDS ARE EXPECTED TO CREATE HIGH PRECIPITATION RATES THAT MAY CAUSE LOCALIZED FLOODING PROBLEMS. ON THE NORTHERN SLOPES A STRONG FOEHN IS EXPECTED TO FORM THAT IS LIKELY TO PRODUCE SEVERE GUSTS EVEN IN THE LOWER VALLEYS.

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