CONVECTIVE FORECAST
VALID 00Z SUN 01/06 - 06Z MON 02/06 2003
ISSUED: 31/05 18:01Z
FORECASTER: HAVEN

GENERAL THUNDERSTORMS ARE FORECAST ACROSS WESTERN, CENTRAL AND PARTS OF SOUTHERN AND EASTERN EUROPE

SYNOPSIS

UPPER RIDGE OVER WESTERN EUROPE IS SLOWLY SHIFTING WEST, AS WELL AS ATLANTIC LONGWAVE UPPER TROUGH. LATTER FEATURE WILL BECOME INCREASING NEGATIVELY TILTED AND REACH THE SOUTHWESTERN BRITISH ISLES AND WESTERN-FRANCE LATER ON SUNDAY. FURTHER EAST...ACTIVE SHORTWAVE OVER NORTHWEST-RUSSIA CONTINUES EAST. AT LOWER LEVELS... COLDFRONT, SUNDAY 06Z OVER IRELAND WILL MOVE SLOWLY EAST AND IS EXPECTED FROM HEBRIDES VIA CORNWALL TO BRITTANY AT 00Z. NORTHEASTWARD MOVING (BAROCLINIC) CONVERGENCE LINE FROM CENTRAL ENGLAND TO WESTERN FRANCE WILL REACH SOUTHWESTERN BENELUX MONDAY NIGHT.

DISCUSSION

...SOUTHERN ENGLAND, PARTS OF NORTHERN AND CENTRAL FRANCE...
THUNDERSTORMS ARE EXPECTED TO FORM NEAR CONVERGENCE LINE AND NEAR COLDFRONT DURING THE DAY AS PRE-FRONTAL CAPE WILL CLIMB BETWEEN 1000 AND 2000 J/KG OVER FRANCE AND BETWEEN 500 AND 1000 J/KG OVER SOUTHERN ENGLAND IN THE AFTERNOON. STRONG DYNAMIC FORCING NEAR COLDFRONT WILL PROBABLY LEAD TO A LARGE STRATIFORM PRECIPITATION AREA, WHILE THE STORMS NEAR THE PRE-FRONTAL CONVERGENCE LINE WILL BE ISOLATED IN THE FIRST PHASE, BUT BECOMING MORE CLUSTERED IN THE EVENING. DEEP LAYER SHEAR IS EXPECTED TO INCREASE AS BAROCLINIC ZONE MAKES PROGRESS TO THE EAST, WITH 0-6KM UNIDIRECTIONAL SHEAR OF 35-40 KT IN THE EVENING OVER SOUTHERN-ENGLAND. MOST LIKELY MODE OF STORMS WILL BE MULTICELLS WITH WINDGUSTS NEAR SEVERE LIMITS AND SMALL HAIL WITH THE STRONGER STORMS. WITH FAVOURABLE 0-1 KM SHEAR, FORMATION OF MESOCYCLONES CANNOT BE RULED OUT, BUT DOESN'T SEEM LIKELY AT THE MOMENT. OVER FRANCE SHEAR WILL BE LESS, HOWEVER...GIVEN THE LARGER INSTABILITY OVER THAT AREA, SOME STORMS MAY BECOME PULSE SEVERE, WITH MARGINAL SEVERE HAIL POSSIBLE. THE FAIRLY HIGH CAPE AND AND DRY MIDLEVELS WILL SUPPORT STRONG WINDGUSTS NEAR SEVERE LEVELS. ORGANIZATION INTO A SSW-NNE MOVING SQUALL LINE OVER THE SLIGHT RISK AREA IS POSSIBLE SINCE FORCING WILL BE LINEAR AND WINDS SHOW LITTLE VEERING WITH HEIGHT. STRONG UVM WILL KEEP STORMS GOING IN THE EVENING AND NIGHT, WHICH WILL REACH AS FAR EAST AS THE WESTERN BENELUX.

...CENTRAL EUROPE...
SUFFICIENT LIFT IS EXPECTED TO KEEP GOING PREVIOUS NIGHT THUNDERSTORMS IN THE MORNING HOURS DUE TO PASSING SHORTWAVE. STORMS SHOULD INCREASE IN COVERAGE AND INTENSITY BY DAYTIME-HEATING, WHICH WILL RESULT IN CAPES CLIMBING TO NEAR 1000 J/KG. SOME LARGER CLUSTERS MAY BE POSSIBLE LATER IN THE AFTERNOON AND EVENING. MAJORITY OF THE STORMS WILL LIKELY BE SHORTLIVED, DUE TO THE WEAK SHEAR. THE COMPLEX TERRAIN AND INTERFERENCE OF MANY OUTFLOWBOUNDARIES CAUSED BY PREVIOUS CONVECTION COULD LOCALLY ENHANCE LOW-LEVEL SHEAR. TOGETHER WITH PRESENT WBZ-HEIGHTS OF NEAR 8000 FT, LOCALLY MARGINAL LARGE HAIL WITH THE STRONGER STORMS IS POSSIBLE, BUT A SLIGHT RISK IS NOT NECESSARY.

...NORTHWEST RUSSIA...
STRONG UVM IS EXPECTED OVER PARTS OF NORTHWEST-RUSSIA DUE TO STRONG DCVA AND WAA AHEAD OF SOUTHEASTWARD MOVING COLDFRONT. ALTHOUGH INSTABILITY IS QUITE LOW, DEEP LAYER SHEAR WILL BE PRESENT TO SUPPORT ORGANIZED STORMS, PERHAPS INTO A SQUALL-LINE WITH WINDGUSTS NEAR SEVERE LIMITS LIKELY. GIVEN THE SHEAR, THERE IS A SLIGHT CHANCE FOR (EMBEDDED) SUPERCELLS, BUT LOW CAPE PRECLUDES A CATEGORICAL RISK AT THE MOMENT.

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