CONVECTIVE FORECAST - UPDATE
VALID 10Z MON 28/04 - 06Z TUE 29/04 2003
ISSUED: 28/04 10:18Z
FORECASTER: GROENEMEIJER

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF FRANCE AND THE BENELUX

GENERAL THUNDERSTORMS ARE FORECAST ACROSS PARTS OF THE BRITISH ISLES, NORTHWESTERN AND NORTHERN IBERIA, FRANCE, THE BENELUX, PARTS OF DENMARK, MUCH OF GERMANY AND NORTHWESTERN SWITZERLAND.

GENERAL THUNDERSTORMS ARE FORECAST ACROSS PARTS OF POLAND, LITHUANIA, BELARUS, UKRAINE, SLOVAKIA, MOLDOVA, ROMANIA AND BULGARIA.

SYNOPSIS

A LONGWAVE IS APPROACHING WESTERN EUROPE FROM THE ATLANTIC. A SURFACE CYCLONE OVER THE BAY OF BISCAY WILL MOVE NORTHWARD AND BE SITUATED OVER SCOTLAND AROUND 18Z. A WEAKLY AMPLIFIED UPPER TROUGH IS PROPAGATING EASTWARD OVER EASTERN EUROPE.

DISCUSSION

...SLIGHT RISK AREA...
STRONG THETA-E ADVECTION IS PRESENTLY OCCURRING OVER FRANCE. A WARM FRONT ALONG A LINE FROM LE HAVRE TO STRASBOURG AT 9Z IS EXPECTED TO LIFT NORTHWARD. AIR-MASS WILL DESTABILISE FROM THE WEST AS SLIGHT COLD-ADVECTION AT 700 IS FORECAST OVER A WARMING BOUNDARY LAYER. CONSIDERABLE INSTABILITY WILL FORM OVER A ZONE FROM SOUTHWESTERN FRANCE TO THE SOUTHERN BENELUX AND SOME ELEVATED INSTABILITY WILL BE PRESENT FARTHER NORTH. ON APPROACH OF UPPER TROUGH...CONVECTION WILL INITIATE OVER SOUTHWESTERN AND CENTRAL FRANCE IN THE EARLY AFTERNOON. DURING EARLY EVENING CONVECTION MAY ALSO DEVELOP OVE NORTHERN FRANCE/SOUTHERN BENELUX. GIVEN HIGH /~50-60 KT SFC-6KM/ BULK SHEAR SOME STORMS WILL LIKELY BECOME SUPERCELLS. THE STORMS WILL BE ACCOMPANIED BY DAMAGING GUSTS AND LARGE HAIL. THE THREAT OF TORNADOES SEEMS RELATIVELY LOW GIVEN RATHER HIGH LCL HEIGHTS. A SMALL THREAT OF TORNADOES EXISTS OVER CENTRAL AND NORTHERN BENELUX NEAR THE WARM FRONT WHERE HIGHER LOW-LEVEL HELICITY IS PRESENT AND LCL'S ARE LOWER. GIVEN STRONG FORCING, CONVECTION WILL LIKELY CLUSTER INTO LINEAR MCS'S MOVING NORTHEASTWARD DURING THE EVENING AND OVERNIGHT. DURING THIS STAGE, THERE IS A CHANCE OF HIGH WIND GUSTS WINDS WILL BE THE LARGEST THREAT.

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