CONVECTIVE FORECAST
VALID 06Z TUE 13/05 - 06Z WED 14/05 2003
ISSUED: 12/05 21:42Z
FORECASTER: DAHL
THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS E CENTRAL EUROPE ... N BALKAN STATES ... N MEDITERRANEAN.
GENERAL THUNDERSTORMS ARE FORECAST ACROSS WESTERN ... CENTRAL ... AND EASTERN EUROPE.
GENERAL THUNDERSTORMS ARE FORECAST ACROSS THE IBERIAN PENINSULA.
SYNOPSIS
INTENSE UPPER TROUGH OVER NW EUROPE WILL CONTINUE TO DIG SE. INTENSE VORT MAX AT THE PERIPHERY OF THIS TROUGH IS EXPECTED TO REACH N ITALY BY WEDNESDAY 06Z. WEAK ILL-DEFINED VORT MAXIMA WILL AFFECT THE SE AND S CENTRAL MEDITERRANEAN SEA. SFC LOW ASSOCIATED WITH THE MAIN UPPER TROUGH WILL NOT MAKE MUCH EASTWARD PROGRESS DURING THE PERIOD ... THOUGH TRAILING MAIN COLD FRONT /ATTM PARALLELING THE CONTINENTAL-EUROPEAN NW ATLANTIC COAST/ WILL ACCELERATE EAST AHEAD OF ANOTHER VORT MAX AT THE PERIPHERY OF THE MAIN TROUGH ... AND EXTEND FROM THE BALTIC SEA ACROSS E POLAND INTO THE N MEDITERRANEAN SEA TOWARDS THE END OF THE FCST PERIOD. THE COLD FRONT APPEARS TO HAVE A DOUBLE STRUCTURE ... WITH A NARROW BELT OF MODIFIED SUBPOLAR AIR BETWEEN THE SUBTROPICAL AIR TO THE EAST ... AND MARITIME POLAR AIR TO THE WEST. AS THE COLD FRONT PROGRESSES EAST ... THIS PLUME WILL FURTHER NARROW AND EVENTUALLY DIAPPEAR LATE IN THE DAY. CYCLOGENESIS IS PROGGED TO OCCUR IN THE LEE OF THE ALPS AHEAD OF THE VORT MAX ON TUESDAY NIGHT.
DISCUSSION
...EAST-CENTRAL AND EASTERN EUROPE...
FAIR CHANCES OF DEEP CONVECTION WILL CONTINUE TO EXIST ACROSS THE EASTERN PORTIONS OF EUROPE WHERE WEAKLY TO MODERATELY UNSTABLE AIRMASS IS PRESENT. SOUNDINGS INDICATE DEEPLY MIXED SUBCLOUD LAYER AND WEAK CIN. AS THE TROUGH PROGRESSES EAST ... SHEAR WILL STRONGLY INCREASE DURING THE DAY. PRIMARY BAND OF DCVA WILL CROSS THE REGION LATE IN THE DAY ... BUT WEAK SHEETS DCVA ARE EXPECTED TO BE PRESENT AHEAD OF THIS BAND. THIS SUGGESTS THAT TSTMS WILL LIKELY BE QUITE NUMEROUS OVER E-CENTRAL EUROPE AHEAD OF THE COLD FRONT. BEST ORGANIZED CONVECTION SHOULD DEVELOP ALONG THE COLD FRONT THOUGH. POTENTIAL PROBLEM WILL BE THAT PREVIOUS CONVECTION CONTAMINATES THE THERMODYNAMIC ENVIRONMENT AHEAD OF THE FRONT. IF AIRMASS HAPPENS TO BE SUFFICIENTLY STRONG CAPPED ... STORMS ALONG THE COLD FRONT WILL PROFIT FROM CAPES IN THE 1000 TO 1500 J/KG RANGE.
CURRENT THINKING IS THAT ISOLATED ... MAINLY DIURNALLY DRIVEN TSTMS WILL BE INITIATED OVER THE HILLY TERRAIN OF E-CENTRAL EUROPE. THESE STORMS WILL POSE THE THREAT OF VERY GUSTY WINDS ALONG WITH SOME HAIL. 0-3 KM SRHS ON THE ORDER 300 M2/S2 ARE FCST ACROSS SE POLAND LATE IN THE DAY BY GFS AHEAD OF WEAK SFC PRESSURE TROUGH. AUGMENTATION WILL BE EASILY REALIZED OVER THE MOUNTAINOUS TERRAIN ... AND STORMS WILL HAVE THE POTENTIAL TO BECOME SUPERCELLULAR ... AND PRODUCE LARGE HAIL AND POSSIBLY A TORNADO IF LOCALLY MORE AMPLE LOW-LEVEL MOISTURE IS ENCOUNTERED.
STORMS ALONG THE FRONT MAY ALSO CONTAIN MESOCYCLONES ESPECIALLY IF SMALL-SCALE RIBBONS OF HIGH SRH CAN BE PICKED UP. STORMS WILL POSE THE THREAT OF STRONG/DAMAGING WIND GUSTS AND LARGE HAIL. LATE IN THE DAY/EVENING PRIMARY THREAT SHOULD SHIFT TOWARDS DAMAGING WIND GUSTS AS LEWPY SQUALL LINE MAY DEVELOP. STORMS SHOULD GRADUALLY WEAKEN AFTER/WITHIN 13/10Z TO 14/00Z TIME FRAME.
...CENTRAL AND WESTERN EUROPE...
FARTHER WEST IN DEEPLY MIXED POLAR AIR MASS AND IN NARROW PLUME OF SUBPOLAR AIRMASS ... THERMODYNAMIC PROFILES WILL BE MUCH LESS CONDUCTIVE TO SEVERE STORMS THAN FARTHER EAST BUT DEEP-LAYER SHEAR OF ABOUT 70+ KNOTS WILL YIELD POTENTIAL FOR SOME STRONG WIND GUSTS AND HAIL. PAST SIMILAR CASES HAVE SUGGESTED THAT LOW-LEVEL HELICITY VARIABILITY IS VERY LARGE ... AND ALTHOUGH MEAN SRH WILL NOT BE VERY IMPRESSIVE ... LOCAL FLOW PERTURBATIONS SHOULD REALIZE SEVERAL HUNDRED M2/S2 OF SRH ... AND THERE IS A SMALL CHANCE OF BRIEF MESOCYCLONIC STORMS THAT WOULD PRODUCE LARGE HAIL ... DAMAGING WIND GUSTS AND TORNADOES. ACTIVITY SHOULD DIMINISH AFTER DARK.
...SPAIN...
A FEW DIURNAL TSTMS ARE EXPECTED AGAIN ... HOWEVER ... SHEAR AND CAPE WILL GENERALLY BE QUITE WEAK AND ALLOVER SEVERE THREAT IS QUITE LOW. HOWEVER ... HIGH LCL HEIGHTS AND DEEP DRY-ADIABATIC SUBCLOUD LAYER SUGGESTS THERE MAY OCCUR SOME STRONG/DAMAGING WIND GUSTS.
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