VALID 15Z SUN 20/10 - 00Z MON 21/10 2002
ISSUED: 20/10 14:49Z
FORECASTER: GATZEN

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS WESTERN IBERIAN PENINSULA

GENERAL THUNDERSTORMS ARE FORECAST ACROSS IBERIAN PENINSULA

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS BISCAYA BAY/ WESTERN FRANCE

SYNOPSIS

INTENSE UPPER TROUGH PLACED OVER NORTHERN EUROPE ... AND COLD POLAR AIRMASS HAS FLOODED WHOLE NORTHERN EUROPE AND CENTRAL EUROPE. SEVERAL WEAK SHORT-WAVE TROUGHS ARE ROTATING ALONG THE EDGE OF THAT SYSTEM. OVER NORTHEASTERN ATLANTIC ... A CUT OFF AND PARTS OF EX-HURRICAN KYLE HAVE FORMED NEW INTENSE LOW, PROPAGATING SLOWLY NORTHEASTWARD AND CAUSING STRONG THETA-E-ADVECTION ESPECIALLY OVER WESTERN EUROPE. WEAK BLOCKING RIDGE OVER WESTERN EUROPE IS FORECASTED TO DISAPPEAR TILL TOMORROW SO THAT NORTHERN ATLANTIC FRONTAL ZONE SHOULD REACH CENTRAL EUROPE.

DISCUSSION

...IBERIAN PENINSULA...
STRONG SOUTHWESTERLY FLOW OVER THE FORECAST AREA IN ADDITION WITH ADVECTION OF HIGH THETA-E ORIGINATED FROM SUBTROPICAL ATLANTIC LEADS TO WIDESPREAD THUNDERSTORM ACTIVITY ALONG THE COLD FRONT OF EX-KYLE, REACHING PORTUGAL AND WESTERN SPAIN. COLD FRONT IS FORECASTED TO CROSS NORTHERN/ WESTERN SPAIN AND WESTERN FRANCE TILL TOMORROW MORNING WHILE PRE-FRONTAL CONVERGENCE IS FORECASTED TO WEAK. ALONG THE COLD FRONT THUNDERSTORMS SHOULD BE LIKELY. ON THE OTHER HAND TEMPS SHOW HUGE CAP ABOVE MOIST BOUNDARY LAYER AND ONLY SMALL VALUES OF CAPE OVER WESTERN/ SOUTHERN PENINSULA ... HOWEVER ... SOME THUNDERSTROMS HABE FORMED ALONG PENINSULA'S COAST AND SHOULD PROPAGATE NORTHEASTWARD. GIVEN VERY STRONG SHEAR IN THE ORDER OF 50..70 KNOTS IN THE LOWEST KILOMETERS, ORGANISED THUNDERSTORMS SHOULD FORM ... AND A FEW SUPERCELLS SHOULD BE POSSIBLE IF OROGRAPHIC EFFECTS WILL ENHANCE SRH. HEAVY RAINFALLS, BIG HAIL AND A FEW WATERSPOUTS/ TORNADOS ARE LIKELY WITH THIS CONVECTION. IN THE EVENING ... FRONTAL SYSTEM REACHES CENTRAL SPAIN, WHERE DRY BOUNDARY-LAYER AND DIJOURNAL COOLING SHOULD REDUCE CAPE AND THUNDERSTORMS SHOULD WEAK.

...WESTERN FRANCE...
STRONG THETA-E-ADVECTION WILL REMAIN IN ADDITION WITH PROPAGATING SHORT-WAVE-TROUGH WHICH SHOULD REACH THE REGION ON LATE AFTERNOON/ EARLY EVENING. MODELS SHOW STRONG UPWARD VERTICAL MOTION OVER BISCAY. EVEN GIVEN DRY BOUNDARY LAYER AS INDICATED BY 00-Z-SOUNDINGS ... ELEVATED STORMS SHOUD BE LIKELY ... AND PROBABLY ROUT INTO THE BOUNDARY LAYER. SMALL FRONTAL WAVE FARECASTED BY BRACKNELL 06-Z-RUN COULD LEAD TO SOUTHERLY/ SOUTHEASTERLS WINDS IN FRONT OF THE COLDFRONT ... AND STRONG LOW-LEVEL SHEAR MAKES SUPERCELLS LIKELY. BIG HAIL; STRONG WIND GUSTS AND A FEW WATERSPOUTS/ TORNADOS SHOULD BE POSSIBLE.

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