CONVECTIVE FORECAST
VALID 06Z TUE 15/04 - 06Z WED 16/04 2003
ISSUED: 14/04 21:40Z
FORECASTER: DAHL

GENERAL THUNDERSTORMS ARE FORECAST ACROSS SW EUROPE.

GENERAL THUNDERSTORMS ARE FORECAST ACROSS IRELAND.

SYNOPSIS

BUILDING UPPER RIDGE OVER CENTRAL EUROPE IS PROGGED TO REMAIN QUASI-STATIONARY ... WITH THE UPPER TROUGH ATTM OVER IBERIA EXPECTED TO CLOSE OFF INTO A CUT-OFF LOW. ANOTHER CLOSED UPPER LOW WILL AFFECT THE EASTERN MEDITERRANEAN BUT SHOULD MOVE OUT OF THE FCST AREA DURING THE PERIOD. AT LOW LEVELS ... LARGE HIGH-PRESSURE AREA COVERING EASTERN AND CENTRAL PARTS OF EUROPE ... WITH WEAK PLUMES OF SUBTROPICAL AIR ADVECTING NORTHWARDS FROM THE WESTERN MEDITERRANEAN INTO FRANCE AND THE BRITISH ISLES AT THE WESTERN PERIPHERY OF THE HIGH PRESSURE AREA.

DISCUSSION

...WESTERN EUROPE...
FOCUS FOR CONVECTIVE ACTIVITY WILL LIKELY BE THE DEVELOPING UPPER LOW OVER S IBERIA ... AMPLE VORT MAX AT THE PERIPHERY OF THIS FEATURE SHOULD HELP MAINTAINING MARGINAL CAPE OVER THE W MEDITERRANEAN. TSTMS SHOULD FORM WITHIN WEAK THETA-E PLUME STRETCHING ACROSS THE WESTERN MEDITERRANEAN SEA E OF THE UPPER LOW ... AND BENEATH THE UPPER COLD POOL OVER THE IBERIAN PENINSULA. DYNAMICS WILL NOT BE TOO IMPRESSIVE PER 12Z MODEL GUIDANCE AND DEGREE OF QG FORCING FOR UPWARD MOTION AS WELL AS THE DEGREE OF DEEP-LAYER SHEAR SHOULD BE RATHER MODEST. HOWEVER ... E OF THE THETA-E PLUME ... STRONGLY BACKED WINDS WILL CREATE FAVORABLY VEERING PROFILES FOR ANY SFC BASED STORM THAT FORMS AT THE EASTERN EDGE OF THE PLUME. THOUGH SPARSITY OF DATA ALLOWS ONLY A ROUGH ESTIMATION OF THE VERTICAL MOISTURE DISTRIBUTION OVER THE S MEDITERRANEAN ... THERE ARE INDICATIONS THAT THE BACKED LOW-FLOW MAY BE RATHER MOIST WITH MEAN-LAYER DEWPOINTS AT OR ABOVE 10 C. PRIND THAT TSTMS OVER THIS REGION WILL TEND TO BE SLIGHTLY ELEVATED ... BUT MAY ROOT DOWN INTO THE BOUNDARY LAYER ... IF THIS HAPPENS ... LOW LCL HEIGHTS AND LOW-LEVEL VEERING WOULD PROVIDE FAVORABLE ENVIRONMENT FOR SUPERCELLS AND LOW-LEVEL MESOCYCLOGENESIS OFF THE ALGERIAN/TUNESIAN NORTH COAST ... ENHANCING THE THREAT OF A FEW TORNADOES ... ISOLATED LARGE HAIL AND SEVERE WIND GUSTS. HOWEVER ... CONFIDENCE IN THIS SCENARIO IS RATHER LOW ATTM ... AND A SLIGHT RISK IS NOT WARRANTED. ALTHOUGH TSTMS BENEATH THE UPPER LOW MAY PRODUCE SOME SMALL HAIL ... WEAK KINEMATIC/THERMODYNAMIC FIELDS SUGGEST MINIMAL THREAT OF ORGANIZED SEVERE.

FARTHER N... WEAK WAA IS EXPECTED OVER FRANCE AND THE EASTERN BRITISH ISLES ... ALTHOUGH SOME 12Z SOUNDINGS INDICATE A SHALLOW ELEVATED MIXED LAYER OVER THE BRITISH ISLES ... LOW-LEVEL THETA-E WILL LIKELY BE TOO LOW TO RENDER UNSTABLE STRATIFICFATION.

IRELAND WILL LIKELY BE AFFECTED BY NORTHWARD MIGRATING SHORT-WAVE TROUGH AT THE MOMENT OVER THE BISCAY ... EXACT TIMING OF THIS FEATURE IS UNCERTAIN ... AND INDICATIONS ARE THAT THE TROUGH WILL HAVE MOVED INTO THE NORTH ATLANTIC ALREADY BY PEAK DAYTIME HEATING. HOWEVER ... CHANCES OF A FEW LOW-TOPPED THUNDERSTORMS EXISTS ESPECIALLY DURING THE AFTERNOON OVER THE NORTHERN PORTIONS OF IRELAND. SEVERE THREAT SHOULD BE MINIMAL GIVEN POOR INSTABILITY/SHEAR PROFILES.

#