DAY 1 CONVECTIVE OUTLOOK
VALID 15Z THU 26/12 - 12Z FRI 27/12 2002
ISSUED: 26/12 14:42Z
FORECASTER: DAHL

GENERAL THUNDERSTORMS ARE FORECAST ACROSS THE SOUTH-CENTRAL MEDITERRANEAN SEA.

GENERAL THUNDERSTORMS ARE FORECAST ACROSS THE IBERIAN PENINSULA.

SYNOPSIS

MAIN FEATURE THIS PERIOD WILL BE DIGGING UPPER LONGWAVE TROUGH ATTM OVER THE CNTRL NORTH ATLANTIC... THIS FEATURE WILL REACH THE IBERIAN PENINSULA TOWARDS FRIDAY MORNING...RESULTING IN DEEP SWLY FLOW ACROSS MUCH OF WESTERN AND CENTRAL EUROPE. ELONGATED EXTENSIVE SFC LOW IS ACCOMPANYING THIS TROUGH... AND WILL BE CENTERED OFF THE EUROPEAN WEST COAST NEAR 10W LATITUDE BY FRIDAY 06Z. COLD CONTINENTAL POLAR/ARCTIC AIRMASSES THAT DOMINATED MUCH OF THE EUROPEAN CONTINENT OVER THE PAST WEEKS ARE SLOWLY REPLACED BY MILD/MARITIME AIRMASSES ADVECTING NORTHEAST WITH THE DEVELOPING SWLY FLOW REGIME.

DISCUSSION

...SOUTH-CENTRAL MEDITERRANEAN SEA...
TSTMS CURRENTLY ONGOING OVER THE S CNTRL MEDITERRANEAN SEA BENEATH UPPER THERMAL TROUGH ASSOCIATED WITH WEAK SRN STREAM VORT MAX... LAPSE RATES ARE NEARLY NEUTRAL... AND GIVEN THAT BAND OF MODERATELY STRONG UPPER WINDS WILL LIKELY REMAIN S OF THE REGION WHERE DEEPEST CONVECTION IS OCCURRING... SEVERE EVOLUTION IS QUITE UNLIKELY. HOWEVER... GIVEN RATHER WARM SEA-SFC TEMPS /AROUND 17 TO 20 C/ AND WEAK LOW-LEVEL SHEAR AS WELL AS LOW LCL HEIGHTS... A FEW WATER SPOUTS MAY OCCUR.

...IBERIA...
LIGHTNING NETWORK INDICATED A FEW CG STRIKES ALONG THE COLD FRONT ASSOCIATED WITH ATLANTIC LONG-WAVE TROUGH THIS MORNING... FORCING FOR UPWARD VERTICAL MOTION IS EXPECTED TO STRENGTHEN OVER THE NEXT HOURS... AND ALTHOUGH INSTABILITY IS VERY MEAGER... TSTM ACTIVITY MAY REJUVENILE ALONG THE COLD FRONT LATER TODAY/TONIGHT. VERTICAL SHEAR ALONG THE FRONT IS QUITE IMPOSING... WITH 45 KNOTS AT 850 HPA AND 85 KNOTS AT 400 HPA ALREADY IN PLACE AHEAD OF THE FRONT /REF LISBOA/PORTUGAL 12Z ASCENT/ ... WHICH MAY LOCALLY PROMOTE STRONG WIND GUSTS. REFRAIN FROM ISSUING CATEGORICAL OUTLOOK THOUGH GIVEN EXPECTED LOW COVERAGE OF CONVECTIVE ELEMENTS ALONG THE COLD FRONT.

FARTHER W IN THE POSTFRONTAL ENVIRONMENT... FIELD OF DEEP ENHANCED CUMULUS/CUMULONIMBUS HAS DEVELOPED NEAR THE MAIN VORT MAX... THIS ACTIVITY WILL ADVECT EAST AND AFFECT AT LEAST THE COASTAL REGIONS OF N SPAIN AND PORTUGAL. EXPECT STRONG WIND GUSTS AND SMALL HAIL WITH THE STRONGER CELLS... ALSO... OVER THE COMPLEX TERRAIN OF THE IBERIAN PENINSULA... RIBBONS OF HIGH SR-HELICITY BE LOCALLY BE GENERATED... YIELDING SLIGHTLY ENHANCED POTENTIAL FOR ROTATING UPDRAFTS AND MAYBE A BRIEF TORNADO OR TWO. HOWEVER... ALLOVER SEVERE THREAT IS TOO LOW FOR A SLGT RISK AT THIS TIME.

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