CONVECTIVE FORECAST
VALID 06Z WED 21/05 - 06Z THU 22/05 2003
ISSUED: 20/05 22:53Z
FORECASTER: GROENEMEIJER

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS EASTERN POLAND, PARTS OF BELARUS, EXTREME SOUTHEASTERN ESTONIA, EXTREME WESTERN UKRAINE, EASTERN SLOVAKIA AND NORTHEASTERN HUNGARY

GENERAL THUNDERSTORMS ARE FORECAST ACROSS MUCH OF CENTRAL EUROPE, SCOTLAND, THE NORTHEN ADRIATIC, THE BALKANS, PARTS OF SWEDEN AND FINLAND AS WELL AS EASTERN PARTS BALTIC STATES, PARTS OF THE UKRAINE, BELARUS AND THE RUSSIAN FEDERATION.

SYNOPSIS

DOMINANT UPPER FEATURE IS A HIGHLY AMPLIFIED UPPER TROUGH HAVING ITS AXIS FROM SOUTHERN SCANDINVIA TO THE ADRIATIC REGION. AN UPPER LOW IS EXPECTED TO CUT-OFF FROM THE TROUGH DURING THE SECOND HALF OF THE PERIOD. NEAR AND WEST OF THE TROUGH AN AIR-MASS OF POLAR ORIGIN IS PRESENT THAT CONVECTIVELY MIXES DURING THE DAYTIME HOURS. SOME THUNDER MAY ACCOMPANY THESE STORMS ESPECIALLY NEAR SUBTLE UPPER LEVEL DISTURBANCES. EAST OF THE TROUGH A FRONATL ZONE IS PRESENT TO THE EAST OF WHICH QUITE STRONG THETA-E ADVECTION IS IN PLACE OVER THE EASTERN BALKANS NORTHWARD INTO EASTERN POLAND AND BELARUS.

DISCUSSION

...SLIGHT RISK AREA...
A COLD FRONT WILL BE LOCATED NEAR A LINE FROM VILNIUS TO WARSZAWA, AND A WARM FRONT FROM NEAR THE POLISH-ESTONIAN BORDER EASTWARD INTO CENTRAL BELARUS. THE AIR MASS IN THE WARM SECTOR IS EXPECTED TO BECOME UNSTABLE AS 30HPA MLCAPE RISES TO 500 - 1000 J/KG. CONVECTION IS EXPECTED TO INITIATE DURING THE EARLY AFTERNOON NEAR THE TRIPLE POINT OVER EXTREME NORTHEASTERN POLAND SOUTHWARD ALONG THE COLD FRONT. SOME STORMS WILL ALSO LIKELY INITIATE NEAR THE WARM FRONT. 0-6 KM BULK SHEAR WILL BE ON THE ORDER OF 40-50 KNOTS, WHICH WILL ALLOW SOME STORMS TO BECOME SUPERCELLS. FOR SUPERCELL DEVELOPMENT. SEVERE THREAT IS HIGHEST NEAR THE TRIPLE POINT WHERE 0-3 SRH S.R.-HELICITY IS FORECAST TO BE AS HIGH AS 300 - 400 M2/S2 CREATING THE MOST FAVORABLE CONDITIONS FOR SUPERCELLS THERE. THE CELLS MAY REMAIN DISCRETE FOR A LONG TIME, ESPECIALLY ALONG THE COLD FRONT, GIVEN THAT STORM MOTION VECTORS WILL HAVE A SMALL ANGLE TO THE FRONTAL BOUNDARY, BEFORE CLUSTERING INTO ONE OR MORE MCS'S OVERNIGHT. WET-BULB-ZERO HEIGHTS NEAR 8000 FT ARE FAVOURABLE OF LARGE HAIL. OTHER IMPORTANT THREAT WITH THE ACTIVITY WILL BE SEVERE WIND GUSTS. THERE IS ALSO A SMALL RISK TORNADOES, ESPECIALLY WITH SUPERCELLS DEVELOPING NEAR THE WARM FRONT, WHERE LCL'S ARE THE LOWEST AND SUPERCELLS MAY INTERACT WITH BUOYANCY GRADIENT OF BOUNDARY-LAYER AIR.

...CENTRAL/SOUTHERN BALKANS...
SOME CONVECTIVE DEVELOPMENT IS EXPECTED DURING THE AFTERNOON. 30HPA - MLCAPE VALUES WILL HAVE RISEN TO VALUES ON THE ORDER OF 400 - 800 J/KG IN PLACES. DEEP-LAYER SHEAR AROUND 30 KTS WILL BE SUPPORTIVE OF MULTICELL DEVELOPMENT. THESE STORMS MAY CAUSE SOME STRONG BUT GENERALLY NON-SEVERE GUSTS AS WELL AS SOME HAIL POSSIBLY EXCEEDING THE SEVERE LIMIT OF 2 CM IN PLACES.

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