DAY 1 CONVECTIVE OUTLOOK
VALID 18Z TUE 18/03 - 06Z WED 19/03 2003
ISSUED: 18/03 17:37Z
FORECASTER: DAHL

GENERAL THUNDERSTORMS ARE FORECAST ACROSS ALONG THE PYRENEES.

SYNOPSIS

UPPER LOW ATTM OVER THE SOUTH OF FRANCE HAS DEVELOPED QUITE DIFFERENTLY THAN ANTICIPATED YESTERDAY AND DID NOT AFFECT THE WESTERN MEDITERRANEAN SEA ... THUS THE GENERAL THUNDER OVER THE WESTERN MEDITERRANEAN HAS BEEN DROPPED.

HOWEVER ... MEDITERRANEAN MOISTURE IS ADVECTED WESTWARDS JUST NORTH OF THE PYRENEES WHERE SFC DEWPOINTS HAVE CLIMBED TO NEAR 10 C WITH TEMPS IN THE 15°C RANGE. UPSLOPE FLOW AND WEAK LOW-LEVEL WAA APPEAR TO BE THE PRIMARY FACTORS MAINTAINING WEAK THUNDERSTORMS JUST NORTH OF THE PYRENEES. UNCERTAINTY EXISTS ON THE FURTHER DEVELOPMENT OF THIS ACTIVITY ... MAIN REGION OF LARGE-SCALE DCVA-RELATED UPWARD VERTICAL MOTION SHOULD BE WEST OF THIS ACTIVITY PER AVAILABLE MODEL FIELDS. ON THE OTHER HAND GFS ANTICIPATED THIS SCENARIO REASONABLY WELL ... AND IS GENERATING PRECIP OVER THIS REGION THROUGH MUCH OF THE NIGHT ... HINTING AT THE POSSIBILITY THAT THIS ACTIVITY IS INDEED NOT RELATED TO ASCENT ASSOCIATED WITH DCVA. SO ... ASSUMING THAT THE PRIMARY FACTOR MAINTAINING THIS ACTIVITY IS LOW-LEVEL UPSLOPE FLOW AND WEAK THETA-E ADVECTION ... THIS ACTIVITY MAY SPREAD WEST OVER THE NEXT HOURS AND CONTINUE TO PRODUCE OCCASIONAL LIGHTNING. SEVERE THUNDERSTORMS ARE QUITE UNLIKELY GIVEN VERY MEAGER KINEMATIC AND THERMODYNAMIC SUPPORT ... THOUGH SOME HAIL MAY OCCUR WITH THE STRONGER CELLS AT ELEVATED LOCATIONS IN THE PYRENEES.

STRONG COLD/DRY ADVECTION ASSOCIATED WITH THE VIGOROUS NORTHERLY LOW-LEVEL FLOW ACROSS THE SOUTHERN BALKAN STATES AS WELL AS DOWNSLOPE FLOW IN THE LEE OF THE BALKAN MOUNTAINS HAVE PRECLUDED THE DEVELOPMENT OF A DEEP POSTFRONTAL CONVECTION OVER THE AEGEAN SEA TODAY. AS SURFACE FLOW IS ALREADY WEAKENING ACROSS THE REGION ... LOW-LEVEL MOISTENING MAY BECOME SOMEWHAT MORE EFFECTIVE DUE TO LONGER RESIDENCE TIME OF THE DRY AIRMASS OVER THE WATER BODY ... WHICH IS EXPECTED TO BE COMPENSATED FOR TO A LARGE PART BY CONTINUOUS COLD/DRY ADVECTION THOUGH. ANOTHER VORT MAX IS EXPECTED TO CROSS THE REGION LATER THIS EVENING/NIGHT ... BUT CONFIDENCE THAT DEEP CONVECTION DEVELOPS IS FAIRLY LOW AND A GEN THUNDER OUTLOOK IS NO LONGER NECESSARY.

DISCUSSION

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