CONVECTIVE FORECAST
VALID 06Z WED 18/06 - 06Z THU 19/06 2003
ISSUED: 17/06 19:06Z
FORECASTER: HAVEN

GENERAL THUNDERSTORMS ARE FORECAST ACROSS CENTRAL EUROPE, ITALY AND PARTS OF THE BALKAN STATES

GENERAL THUNDERSTORMS ARE FORECAST ACROSS CENTRAL SWEDEN AND NORTHWEST-RUSSIA

SYNOPSIS

UPPER TROUGH, WEDNESDAY 06Z OVER GERMANY AND NW-ITALY WILL CONTINUE E-SE AND IS EXPECTED FROM SE-POLAND TO THE ADRIATIC SEA EARLY ON THURSDAY. BEHIND THIS FEATURE A STRONG W’LY UPPER FLOW WILL ESTABLISH OVER NW-EUROPE. AT LOWER LEVELS… WEAK COLDFRONT OVER CNTRL NORTHSEA TO CNTRL-FRANCE WILL MAKE SLOW PROGRESS TO THE EAST. COMPLEX AND FLAT PRESSURE DISTRIBUTION OVER CNTRL-EUROPE TO ITALY WHERE SUBTROPICAL AIRMASS IS INPLACE. THE MINOR LOWS AND SFC TROUGHS WILL BE FOCUS FOR TSTMS DEVELOPMENT.

DISCUSSION

...CENTRAL EUROPE...
MOD/STRONG UPPER FORCING WILL KEEP NIGHT-SURVIVING THUNDERSTORMS GOING, WHICH WILL GRADUALLY SPREAD EAST. AS DAYTIME HETATING CONTINUES... MLCAPE WILL CLIMB IN THE 500-1000 J/KG RANGE. 0-6 KM SHEAR WILL BE RATHER POOR, HOWEVER... LOCALLY THE SHEAR IN THE LOWEST 1500M MAY BE ENHANCED BY TOPOGRAPHY OR OUTFLOW-BOUNDARY. IF A STORM MANAGE IT TO GET IN A FAVORABLE PATH THEY MAY BECOME BRIEFLY SUPERCELLULAR WITH HAIL UP TO 3-4 CM POSSIBLE. ALSO WINDGUSTS JUST BELOW SEVERE LEVELS ARE POSSIBLE AS CALCULATED BY GUST REGRESSION FORMULA. THE LOW INSTABILITY AS WELL AS THE VERY CONDITIONAL SCENARIO PREHIBITS A SLIGHT RISK AT THE MOMENT.

...ITALY...
ABUNDANT MOISTURE WILL BE AVAILABLE WITH DEWPOINTS RISING AS HIGH AS 25C IN COASTAL AREAS AND 15-20C FURTHER INLAND. THIS WILL AID TO A QUITE UNSTABLE AIRMASS WITH MLCAPE GENERALLY IN THE ORDER OF 1000-2000 J/KG. SEABREEZES WILL LIKELY INITIATE DEEP CONVECTION IN THE EARLY AFTERNOON. SINCE UVM IS EXPECTED TO BE MODERATE BY THE APPROACHING UPPER TROUGH, THUNDERSTORMS WILL BECOME CLUSTERED AS TIME PROGRESSES. ABSENCE OF DEEP LAYER SHEAR WILL KEEP INDIVIDUAL CELLS RATHER SHORT-LIVED AND NO ORGANIZED SEVERE STORMS ARE EXPECTED. STORMS MAY PRODUCE BRIEF DOWNBURSTS OF HEAVY RAIN WITH LOCAL FLOODING POSSIBLE. IN COASTAL AREAS, WITH EXCESSIVE DEWPOINTS, CAPE MAY REACH VALUES OF 2000-3000 J/KG, WITH STRONG BUT SHORTLIVED UPDRAFTS AS A RESULT. THESE STORMS MAY BE CAPABLE OF PRODUCING LARGE HAIL, BUT ALL OVER THREAT SEEMS TOO LOW FOR A SLIGHT RISK.

...GREECE, ALBANIA, SERBIA...
STEEP LAPSE RATES AND A DRY ENVIRONMENT IN THE LOWEST 3 KM WILL BE SUPPORTIVE OF DRY MICROBURSTS IN THE INTERIOR AREAS. THESE WILL BE VERY ISOLATED HOWEVER, AND IT DOES NOT WARRANT A CATEGORICAL RISK. AS UPPER TROUGH APPROACHES... LIFTING WILL HELP TO INCREASE THE RELATIVE HUMIDITY, AS A RESULT THUNDERSTORMS WILL BECOME MORE WIDESPREAD WITH A FEW BURSTS OF HEAVY RAIN LIKELY.

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