CONVECTIVE FORECAST
VALID 06Z MON 26/05 - 06Z TUE 27/05 2003
ISSUED: 25/05 20:45Z
FORECASTER: GROENEMEIJER
+++AMENDED+++

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF FINLAND PARTS OF RUSSIA, ESTONIA, LATVIA AND LITHUANIA.

GENERAL THUNDERSTORMS ARE FORECAST ACROSS EASTERN SCANDINAVIA, PARTS OF RUSSIA, BELARUS, MUCH OF CENTRAL EUROPE, SOUTHERN FRANCE, PARTS OF ITALY, THE BALKANS, THE UKRAINE AND TURKEY.

SYNOPSIS

A TROUGH IS LIFTING OUT OF THE NORTH SEA AREA ACCELERATING EASTWARD OVER SOUTHERN SCANDINAVIA. A CUT-OFF LOW OVER THE WESTERN MEDITERRANEAN MOVES SLOWLY SOUTHWARD. A WEAK FILLING UPPER LOW IS LOCATED OVER THE EASTERN BALKANS MOVING SLOWLY EASTWARD INTO THE SOUTHERN BLACK SEA AREA.

DISCUSSION

...FINLAND...BALTIC STATES...
NWPS LET THE AIR-MASS OVER MUCH OF FINLAND BECOME LATENTLY UNSTABLE AS THE BOUNDARY LAYER IS WARMED DURING THE DAY. THE APPROACH OF A SUBTLE UPPER-LEVEL VORT MAX IS EXPECTED TO AID IN CONVECTIVE INITIATION BY EARLY AFTERNOON. WIND SHEAR OVER NORTHERN AND CENTRAL FINLAND WILL INCREASE DURING THE DAY. 0-1 KM BULK SHEAR WILL INCREASE TO APPROXIMATELY 25-30 KTS AND 0-6 KM DEEP-LAYER SHEAR WILL BE IN THE 40 - 60 KT RANGE. CURRENT THINKING IS THAT A FEW STORMS WILL FORM OVER WESTERN FINLAND IN THE EARLY AFTERNOON, SOME OF WHICH WILL LIKELY BE SHALLOW SUPERCELLS. THESE WILL CLUSTER INTO ONE OR MORE LINEAR CONVECTIVE SYSTEMS MOVING EASTWARD DURING THE REMAINDER OF THE DAY AND INTO THE EVENING. MAIN THREAT WITH THESE STORMS WILL BE DAMAGING WINDS. A FEW WEAK (F0/F1) TORNADOES WILL ALSO BE POSSIBLE GIVEN LOW LCL HEIGHTS AND STRONG LOW-LEVEL SHEAR. ALSO, SOME HAIL MAY ACCOMPANY THE STORMS, POSSIBLY EXCEEDING THE SEVERE LIMIT OF 2 CM DIAMETER LOCALLY.

FURTHER SOUTH....INSTABILITY WILL BE HIGHER BUT WIND SHEAR WILL BE LESS, HOWEVER STILL SUPPORTIVE OF WELL-ORGANIZED MULTICELLS. MODEL FIELDS INDICATE THE PRESENCE OF VERY DRY AIR AT MID-TROPOSPHERIC LEVELS WHICH WILL BE SUPPORTIVE OF STRONG DOWNBURSTS. ALSO THERE IS INDICATION FOR SOME UPPER-LEVEL SUPPORT FOR CONVECTION SO THAT THE FORMATION OF A SEVERE MCS IS POSSIBLE. MAIN THREAT WILL BE STRONG GUSTS AND A LESSER THREAT WILL BE LARGE HAIL.

...EASTERN SWEDEN...
CURRENT THINKING IS THAT COLDER AIR WILL ENTER EASTERN SWEDEN BEFORE CONVECTIVE DEVELOPMENT OVER THE AREA HAS OCCURRED. IF THE COLD AIR IS SOMEWHAT LATE THAN CURRENTLY ANTICIPATED, THE AREA MAY NEED TO BE INCLUDED IN THE SLGT RISK AREA.

...NORTHERN POLAND...
COLD FRONT OVER NORTHWESTERN POLAND WILL SLOWLY MOVE EASTWARD DURING THE DAY. GFS 12Z RUN LETS 30HPA-MLCAPE INCREASE TO 2000-2500 J/KG AHEAD OF THE FRONT +++BUT THIS SEEMS TO BE TOO HIGH GIVEN THAT GFS ALSO HAS UNREALISTIC SFC DEWPOINTS OF 24C IN THE AREA+++. 0-6 KM BULK SHEAR WILL BE IN THE 25-35 KTS RANGE AND BE SUPPORTIVE OF MULTICELL DEVELOPMENT. PROBLEM IS THAT UPPER LEVEL SUPPORT FOR CONVECTIVE INITIATION SEEMS TO BE QUITE MARGINAL. STILL, A FEW STORMS SHOULD BE ABLE TO FORM TOMORROW AFTERNOON. MAIN RISK OF THE CONVECTION SEEMS TO BE LARGE HAIL, HOWEVER A FEW STRONG, BUT MOSTLY NON-SEVERE GUSTS MAY ALSO OCCUR. GIVEN THE ANTICIPATED LOW COVERAGE OF THE STORMS AND THE LIMITED THREAT A CATEGORICAL RISK IS NOT ISSUED FOR THIS AREA AT THIS MOMENT.

...REPUBLIC OF MOLDOVA, SOUTHEASTERN UKRAINE AND NORTHEASTERN ROMANIA...
INSTABILITY OVER THE AREA WILL BE ON THE ORDER OF 500 - 1200 J/KG IF SUFFICIENT SOLAR HEATING OCCURS. A SUBTLE VORT MAX MOVING WESTWARD FROM THE NORTHERN BLACK SEA MIGHT INITIATE SOME ORGANISED MULTICELLS OVER THE AREA THAT WILL MOVE WESTWARD DURING THE DAY. SOME STRONG BUT GENERALLY NON-SEVERE GUSTS WILL LIKELY OCCUR WITH THE ACTIVITY.

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