DAY 1 CONVECTIVE OUTLOOK
VALID 06Z THU 02/01 - 06Z FRI 03/01 2003
ISSUED: 02/01 01:15Z
FORECASTER: GROENEMEIJER

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTHERN AND WESTERN FRANCE, SOUTHERN BENELUX, CENTRAL GERMANY, WESTERN CZECH REPUBLIC, NORTHERN SWITZERLAND, NORTHWESTERN AUSTRIA

GENERAL THUNDERSTORMS ARE FORECAST ACROSS MUCH OF WESTERN AND WEST-CENTRAL EUROPE INCLUDING NORTHWESTERN IBERIA...AND OVER PARTS OF THE EASTERN MEDITERRANEAN

SYNOPSIS

A BAROCLINIC WAVE WSW OF CORNWALL IS UNDERGOING RAPID CYCLOGENESIS WITHIN A ZONAL JET-STREAM ENTERING WESTERN EUROPE. NORTH OF THE FRONT THE AIR IS COLD DRY AND STABLE AND DO NOT ALLOW THUNDERSTORM FORMATION. THE AIR-MASS SOUTH OF THE FRONTAL ZONE ASSOCIATED WITH THE JET STREAM IS NEUTRAL FOR SATURATED PARCELS TO MARGINALLY UNSTABLE OVER WESTERN EUROPE AND MORE STABLE OVER ELSEWHERE. OVER THE EASTERN MEDITERRANEAN THE AIR IS ALSO MARGINALLY UNSTABLE.

DISCUSSION

...NORTHERN AND WESTERN FRANCE, SOUTHERN BENELUX, CENTRAL GERMANY, WESTERN CZECH REPUBLIC, NORTHERN SWITZERLAND, NORTHWESTERN AUSTRIA...
RAPID CYCLOGENESIS IS EVIDENT ON 2330Z WATER VAPOR IMAGERY ABOUT 250 KMS WSW OF CORNWALL. LATEST UKMO-REGIONAL, GFS AND MM5 MODEL RUNS DEEPEN LOW PRESSURE SYSTEM FAR. MODELS AGREE ON A SCENARIO THAT HAS AN 975 TO 980 HPA LOW OVER NORTHERN NETHERLANDS BY 18Z. LOW WILL THEN TRACK EASTSOUTHEASTWARD. HIGHEST GRADIENT WILL THEN BE SOME DISTANCE SOUTH OF THE CORE OVER NORTHERN FRANCE, SOUTHERN BELGIUM/LUXEMBURG AND CENTRAL GERMANY. MAIN CONVECTIVE DEVELOPMENT IS EXPECTED NEAR COLD FRONT AND NEAR A POSTFRONTAL TROUGH. SOME LATENT INSTABILITY IS EXPECTED TO BE PRESENT WHERE THE HIGH-LAPSE RATE DRY INTRUSION IS PRESENT. NEVERTHELESS, CAPE WILL LIKELY REMAIN BELOW 500 J/KG. BOTH CONVECTION ALONG COLD FRONT AND NEAR THE TROUGH WILL LIKELY BE LINEARLY ORGANISED. HIGH 0-1KM HELICITY VALUES ARE EXPECTED /TO AROUND 250 M2/S2 IN PLACES/. HIGH LOW-LEVEL WIND-SHEAR /AS WINDS AT 850 HPA 850 ARE EXPECTED TO INCREASE TO 50 KNOTS NEAR COLD FRONT AND 70 KNOTS NEAR THE TROUGH/. EMBEDDED SUPERCELLS ARE THEREFORE POSSIBLE WITHIN LINEAR CONVECTION...INCREASING THE THREAT FOR VERY LOCALIZED STRONG DOWNBURSTS AND/OR A TORNADO OR TWO. THE MAIN THREAT HOWEVER WILL BE HIGH WIND GUSTS ASSOCIATED WITH NON-SUPERCELLULAR CONVECTION OF UP TO 70 KNOTS. SOME SMALL HAIL MAY ALSO OCCUR. THE COLD FRONT WILL BE ALONG AFFECT NORTHWESTERN FRANCE FROM 3Z ON. IT WILL BE NEAR A LINE FROM BRUSSELS TO NANTES AT 9Z, NEAR THE RHINE VALLEY AT 15Z AND NEAR WESTERN AUSTRIA/CZECH REPUBLIC AROUND 21Z. THE TROUGH WILL BE 6 TO 9 HOURS LATER.

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