CONVECTIVE FORECAST
VALID 12Z FRI 02/05 - 06Z SAT 03/05 2003
ISSUED: 02/05 12:54Z
FORECASTER: VAN DER VELDE

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTHERN FRANCE, THE BENELUX, AND WESTERN GERMANY

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS ROMANIA, BULGARIA, FORMER YUGOSLAVIA, HUNGARY, MOLDAVIA

SYNOPSIS

VIGOROUS DEPRESSION ENTERING WESTERN EUROPE WITH STRONG PRESSURE GRADIENT OVER THE NORTHERN FRANCE-BENELUX-WESTERN GERMANY CORRIDOR WITH A COLD FRONT OVER NORTHERN FRANCE AT 12Z INTO WESTERN GERMANY AT 18Z. AN OCCLUSION WITH THE STRONGEST WIND FIELD WILL FOLLOW SHORTLY AFTER. ....CYCLONAL FLOW OVER SOUTHEASTERN EUROPE WITH HIGH UPPER LEVEL WINDS AT THE NORTH SIDE (AUSTRIA INTO SOUTHERN POLAND)... CRITICALLY HIGH DEWPOINTS ARE ARISING OVER SOUTHEASTERN EUROPE UNDER VERY DRY AIR WITH STEEP LAPSE RATES, ALLOWING FOR ISOLATED CONVECTION.

DISCUSSION

...NORTHERN FRANCE, THE BENELUX, AND WESTERN GERMANY...
CURRENT 11Z/12Z DEWPOINTS OF 11 DEGREES, TEMPERATURES OF 20 DEGREES COMBINED WITH 00Z TRAPPES SOUNDING SHOW STEEP LOW LEVEL LAPSE RATES AND CONVECTIVE INSTABILITY, WHILE THE WARMER AIR AT MIDLEVELS SHOULD COOL CONSIDERABLY AT THE APPROACH OF THE 500 HPA TROUGH. THE COLD FRONT SHOULD BE THE MAIN TRIGGER IN THE AFTERNOON. AHEAD OF THE COLD FRONT, A SMALL CHANCE THAT SOME STORMS MAY ALREADY FORM -- HOWEVER DECREASING DEWPOINTS TOWARDS ONLY 4-6 DEGREES AHEAD OF THE FRONT IN WESTERN GERMANY MAY FURTHER LIMIT THAT CHANCE. ...HIGHER DEWPOINTS OVER OF AROUND 10 DEGREES OVER THE NETHERLANDS APPEAR TO BE MORE FAVORABLE AND LEFT JET EXIT COULD PROVIDE ADDITIONAL TRIGGERING AND DEEP LAYER SHEAR. 0-1 KM SHEAR SHOULD INCREASE TOWARDS 18Z AT THE COLD FRONT, WHICH IS PROGGED TO HAVE VERY LOW LCLS/LFCS -- WHILE THE MAIN THREAT APPEARS TO BE THE GUSTS --(MORE THAN 50 KTS POSSIBLE) AS THE CONVECTIVE OCCLUSION PASSES DURING THE LATE EVENING OVER THE BENELUX AREA, PERHAPS ASSOCIATED WITH LINEAR ALIGNMENT OF CONVECTION-- AN ISOLATED TORNADO CANNOT BE RULED OUT UNDER THESE CONVECTIVE HIGH SHEAR-LOW LCL-STRONG TRIGGER CIRCUMSTANCES. THE GUST THREAT SHOULD CONTINUE INTO GERMANY AT NIGHT... THE SMALL RISK OF AN ISOLATED TORNADO WILL BE MOSTLY AT THE COLD FRONT DURING DAYTIME OR PERHAPS INTO THE NIGHT OVER NORTHWESTERN GERMANY AT THE LEFT EXIT OF THE JET. ANY CONVECTION OVER NIGHT IN THE BENELUX WOULD POSE A THREAT OF SEVERE GUSTS AND A SMALL CHANCE OF AN ISOLATED TORNADO AS 0-1 KM SHEAR IS FORECAST BY GFS TO BE IN THE ORDER OF 30 KTS.

...ROMANIA, BULGARIA, FORMER YUGOSLAVIA, HUNGARY, MOLDAVIA...
VERY DRY AIR PRESENT IN 00Z SOUNDINGS IN MOST OF THE AREA... WITH CURRENT DEWPOINTS RISING HIGHER THAN 15C...TEMPERATURES > 30 IN THE AREA, SOME STORMS ARE POSSIBLE AND ONE HAS ALREADY DEVELOPED OVER BULGARIA ATTM, SUGGESTING THE CAP IS NOT EVERYWHERE AS STRONG AS 00Z SOUNDINGS SUGGEST. MLCAPE IS EXPECTED TO BE AROUND 500 J/KG, WITH HIGH LFCS, AND IN INTERACTION WITH THE STRONG SHEAR OVER NORTHERN PORTIONS OF THE SLGT AREA, SOME CHANCE FOR ISOLATED HIGH-BASED MULTICELLS AND PERHAPS A FEW SUPERCELLS IS ANTICIPATED. GIVEN THE VERY DRY SOUNDINGS, VERY STRONG THUNDERSTORM OUTFLOW WINDS ARE THE MAIN THREAT WITH ISOLATED MICROBURST EVENTS BECOMING A POSSIBILITY. LARGE HAIL IS THE SECOND THREAT WITH ANY STORM -- THE DRY SUBCLOUD LAYER INHIBITS MELTING OF HAILSTONES BETWEEN CLOUD BASE AND SURFACE. MOUNTAIN RIDGES ARE LIKELY TO PROVIDE THE STRONGEST TRIGGERING FOR ANY STORMS.

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