VALID 11Z MON 11/11 - 06Z TUE 12/11 2002
ISSUED: 11/11 10:32Z
FORECASTER: GROENEMEIJER

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE NORTHERN AND WESTERN PARTS OF THE BRITISH ISLES

GENERAL THUNDERSTORMS ARE FORECAST ACROSS THE BRITISH ISLES

GENERAL THUNDERSTORMS ARE FORECAST ACROSS EASTERN MEDITERRENEAN

SYNOPSIS

AN ATLANTIC LOW NORTHWES OF SCOTLAND /NEAR 60N 13W/ IS THE MOST IMPORTANT FEATURE THIS PERIOD. ALONG ITS SOUTHERN FLANK AN INTENSE SHORTWAVE TROUGH WILL MOVE EASTWARD. MID-LEVEL COLD AIR /-35 C AT 500HPA/ CREATES A MARGINALLY UNSTABLE ATMOSPHERE NEAR AND JUST SOUTH OF THE SYSTEM. ELSEWHERE AIR-MASS IS TOO STABLE FOR THUNDERSTORMS TO DEVELOP.

DISCUSSION

...THE NORTHERN AND WESTERN PARTS OF THE BRITISH ISLES...
VERY COLD AIR OVERSPREADS WARM ATLANTIC SURFACE WATERS YIELDING SOME INSTABILITY IN STRONG WESTERLY FLOW SOUTH OF THE ATLANTIC LOW. AN EMBEDDED TROUGH ASSOCIATED WITH A STRONG JET-STREAK AT MID-LEVELS /80KT @ 500HPA/ IS INDUCING THE DEVELOPMENT OF CONVECTIVE COMMA NORTHWEST OF IRELAND. WARM ADVECTION REGIME EAST OF THIS COMMA GIVES RISE TO SOMEWHAT DEEPER CONVECTION. ANOTHER LESS-DEVELOPED COMMA-LIKE SYSTEM IS ALREADY PRESENT NEAR WESTERN SCOTLAND. ENVIRONMENT IS QUITE STRONGLY SHEARED. MAIN THREAT WILL BE SEVERE GUSTS ON PASSAGE OF COMMA AND PERHAPS ALSO ASSOCIATED WITH LESS ORGANIZED CONVECTION. COLD AIR-MASS TEMPERATURES WILL INHIBIT FORMATION OF SEVERE HAIL.

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