DAY 2 CONVECTIVE OUTLOOK
VALID 06Z SAT 22/03 - 06Z SUN 23/03 2003
ISSUED: 21/03 20:09Z
FORECASTER: DAHL

GENERAL THUNDERSTORMS ARE FORECAST ACROSS THE CENTRAL MEDITERRANEAN REGIONS.

GENERAL THUNDERSTORMS ARE FORECAST ACROSS THE IBERIAN PENINSULA.

SYNOPSIS

UPPER LONG-WAVE RIDGE CENTERED OVER THE NORTH SEA ... ASSOCIATED WITH AN OMEGA-BLOCK PATTERN IS SLOWLY MOVING EAST ... THEREBY REBUILDING THE BLOCK. RESULTANT ENHANCED LOW-LEVEL NORTHERLY FLOW STRETCHING ACROSS THE ENTIRE EASTERN HALF OF EUROPE AND RUSSIA ... IS ADVECTING CONTINENTAL POLAR AIRMASSES INTO THE BALKAN STATES AND THE ADRIATIC SEA DURING THE FCST PERIOD. DEVELOPING UPPER CUT-OFF LOW ATTM OVER FRANCE IS EXPECTED TO SHIFT WEST INTO THE GULF OF BISKAY ON SATURDAY ... WHILE UPPER LOW OFF THE MOROCCAN ATLANTIC COAST ... WILL SHIFT EAST INTO ALGERIA. VORT MAX AT THE EASTERN PERIPHERY OF THE UPPER RIDGE ... WILL RAPIDLY DIG SOUTHWARD AND AFFECT THE CENTRAL MEDITERRANEAN REGIONS ON LATE SATURDAY.

DISCUSSION

...MEDITERRANEAN...
PRIMARY FEATURE ON SATURDAY APPEARS TO BE A VIGOROUS VORT MAX EXPECTED TO REACH THE CENTRAL AND SOUTH MEDITERRANEAN REGIONS TOWARDS THE AFTERNOON. WITH THE ADVENT OF THIS FEATURE ... COLD FRONT ATTM OVER THE NORTHERN MEDITERRANEAN REGIONS WILL ACCELERATE SOUTH AND REACH S ITALY AND GREECE TOWARD THE END OF THE PERIOD. BEST POTENTIAL FOR CONVECTIVE DEVELOPMENT APPEARS TO EXIST ALONG AND AHEAD OF THIS FRONT DOWNSTREAM OF THE VORT MAX. INDICATIONS ARE THAT PREFRONTAL MODIFIED MIXED POLAR AIRMASS IS ESSENTIALLY NEUTRALLY STRATIFIED ... ATTM UP TO AROUND 500 HPA. UVV'S AND CONCOMMITANT MID/UPPER COOLING SHOULD DEEPEN THIS MIXED LAYER ... YIELDING HIGH ENOUGH EQUILIBRIUM LEVELS FOR SHOWERS AND THUNDERSTORMS TO FORM. FCST THICKNESS ADVECTION FIELDS SUGGEST THAT A WEAK FRONTAL WAVE WILL FORM NEAR GREECE ALONG THE COLD FRONT ... AND BULK OF PRECIP ASSUMED BY THE MODELS APPEARS TO BE ASSOCIATED WITH THE DEVELOPING WARM ADVECTION REGIME N OF THE FRONTAL BOUNDARY. CURRENT THINKING IS THAT A FEW LOW-TOPPED THUNDERSTORMS WILL FORM AHEAD OF THE VORT MAX ALONG AND S OF THE COLD FRONT. ACTIVITY SHOULD STRENGTHEN DURING THE NIGHT WHEN KINEMATIC FIELDS BECOME MORE SUPPORTIVE TO ORGANIZED THUNDERSTORMS AND AS FORCING FOR UPWARD MOTION INCREASES. IF CONVECTION DOES FORM ... IT MAY BRIEFLY DEVELOP INTO BOW ECHOES/LEWP'S AND PRODUCE ISOLATED MARGINALLY SEVERE WIND GUSTS ALONG WITH SOME HAIL. HOWEVER ... CONFIDENCE IN THIS SCENARIO IS TOO LOW ATTM TO WARRENT A SLGT RISK.

...IBERIA...
TSTMS ATTM APPROACHING S SPAIN ... APPEAR TO BE ASSOCIATED WITH WARM-ADVECTION REGIME IN ADVANCE OF THE EASTWARD PROPAGATING UPPER LOW. ASSUMING THAT LOW-LEVEL WARM-ADVECTION WILL BE STRONGEST EARLY IN THE MORNING WHEN LOW-LEVEL FLOW IS DECOUPLED FROM THE BOUNDARY LAYER ... A FEW SLIGHTLY ELEVATED TSTMS MAY BE ONGOING AT THE BEGINNING OF THE PERIOD OVER SOUTHERN AND WESTERN IBERIA. PRESENT THINKING IS THAT MOISTURE INFLUX INTO SPAIN IN THE BOUNDARY LAYER WILL BE LIMITED AS RATHER DRY EASTERLY SFC FLOW SHOULD BE IN PLACE ... AND SFC BASED CONVECTION APPEARS RATHER UNLIKELY ATTM. HOWEVER ... LATER RAOB DATA HAVE TO BE AWAITED TO SPECIFY CHANCE OF SFC-BASED CONVECTIVE DEVELOPMENT DURING THE DAY. STRONGEST WAA APPEARS LIKELY TO OCCUR OVER THE WESTERN HALF OF IBERIA OVER THE NIGHT ... AND A FEW ELEVATED TSTMS SHOULD SHOULD DEVELOP AGAIN.

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