CONVECTIVE FORECAST
VALID 06Z SAT 24/05 - 06Z SUN 25/05 2003
ISSUED: 23/05 19:34Z
FORECASTER: HUGO

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF GREECE & W=ERN TURKEY

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL/W=ERN UKRAINE, MALDOVA, ROMANIA, N=ERN BULGARIA, YUGOSLAVIA, BOSNIA HERCEGOVINA, CROATIA, SLOVENIA & HUNGARY

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL/E=ERN GERMANY, SWITZERLAND, W=ERN AUSTRIA, W=ERN CZECH REPUBLIC & S=ERN DENMARK

GENERAL THUNDERSTORMS ARE FORECAST ACROSS ALL PARTS OF EUROPE *EXCEPT* THE SLGT RISK REGIONS & CENTRAL FRANCE, W=ERN IRELAND, CENTRAL & NW SPAIN, N=ERN SCANDINAVIA & PARTS OF W=ERN RUSSIA

SYNOPSIS

A FILLING LONG WAVE TROUGH OVER THE BRITISH ISLES WILL SLOWLY MOVE NE=WARDS TOWARDS SW=ERN PARTS OF SCANDINAVIA EVENTUALLY DEVELOPING ANTICYCLONIC TROUGH DISRUPTION OVER SPAIN BY 251200Z THUS ALLOWING RISING CONTOUR HEIGHTS INTO SW=ERN REGIONS OF THE BRITISH ISLES & FRANCE...A GENERAL SLACK 500MB CONTOUR PATTERN COVERS THE REST OF EUROPE WITH A SLACK CLOSED 500MB LOW PRESSURE OVER GREECE & PARTS OF TURKEY...STRONG JET OVER PARTS OF NW=ERN EUROPE IN ASSOCIATION WITH THE SURFACE LOW PRESSURE AND 500MB TROUGH WITH A WEAK JET OVER PARTS OF GREECE & TURKEY IN ASSOCIATION WITH THE SLACK SURFACE AND 500MB LOW PRESSURE.

DISCUSSION

...GREECE & W=ERN TURKEY...
A SLACK SURFACE LOW PRESSURE WITH EMBEDDED TROUGHS WILL DOMINATE OVER GREECE AND TURKEY DURING THE DAY...FORECAST SOUNDINGS SHOW MLCAPE VALUES OF BETWEEN 300 AND 400J/KG WITH SBCAPE VALUES BETWEEN 400 AND 600J/KG...CONVECTION WILL INITIATE DURING THE LATTER STAGES OF THE MORNING AND INTO THE EARLY AFTERNOON...WITH LITTLE OR NO DEEP LAYER SHEAR (0-6KM <20KT) NO MAJOR ORGANISATION IS EXPECTED HOWEVER SOME POTENT SINGLE CELLS ARE EXPECTED BY LATE AFTERNOON...TORRENTIAL RAINFALL, GUSTY SURFACE WINDS (FCST T2GUST 30-40MPH) AND MODERATE SIZED HAIL DUE TO FAVOURABLE WBZ HEIGHTS (5000-7000FT) ARE ALL POSSIBLE WITHIN THE SLGT RISK REGION...CONVECTION WILL SLOWLY DECAY TOWARDS SUNSET.

...E=ERN EUROPE; UKRAINE, MOLDOVA, YUGOSLAVIA......
SLACK PRESSURE GRADIENTS ACROSS THE SLGT RISK REGION WILL AGAIN LEAD TO DIURNALLY INDUCED CONVECTIVE DEVELOPMENT...WITH FCST SURFACE TEMPERATURES EXPECTED TO REACH THE UPPER 70'S AND EARLY 80'S SOME LARGE CAPE VALUES ARE EXPECTED...MLCAPE IS EXPECTED TO BE BETWEEN 800 AND 1000J/KG WITH SBCAPE POSSIBLE PASSING AN INTENSE 2000J/KG WITH LI'S VARYING BETWEEN -3 AND -6C...CONVECTION WILL INITIATE DURING THE LATTER STAGES OF THE MORNING AND INTO THE EARLY AFTERNOON...SOME LIMITED REGIONS OF LOW LEVEL SHEAR (0-1KM 15-20KT) AND DEEP LAYER SHEAR (0-6KM 25-35KT) WOULD PERMIT SOME MULTICELL DEVELOPMENT BUT SUPERCELL DEVELOPMENT ISN'T EXPECTED DUE TO LOW HELICITY VALUES...TORRENTIAL RAINFALL IS LIKELY AND POSSIBLY LEADING TO SOME LOCALISED FLOODING...WBZ HEIGHTS OF BETWEEN 8000 AND 9000FT ALONG WITH THE INTENSE CAPE VALUES WOULD LEAD TO SOME MODERATE TO LARGE SIZED HAILSTONE...GUSTY SURFACE WINDS ARE ALSO EXPECTED WITH A T2GUST FCST MAX SPEEDS OF BETWEEN 40 AND 50MPH...CONVECTION WILL PERSIST THROUGH A LARGE PART OF THE EVENING AND FOR A TIME DURING THE NIGHT ESPECIALLY IN ASSOCIATION WITH ANY MULTICELL DEVELOPMENT BEFORE GRADUALLY WEAKENING.

...CENTRAL/EAST GERMANY, SWITZERLAND, PARTS OF DENMARK...
A SLACK PRESSURE GRADIENT ACROSS THE ABOVE REGIONS IS EXPECTED WITH A FRONTAL WAVE FEATURE MAKING LITTLE OR NO PROGRESS ACROSS GERMANY DURING THE COURSE OF THE DAY...A CLOSED REGION OF SLACK LOW SURFACE PRESSURE IS EXPECTED TO DEVELOP ACROSS GERMANY DURING THE LATTER STAGES OF THE FCST PERIOD AHEAD OF THE FRONTAL WAVE...CONVECTION WILL DEVELOP DURING THE LATTER STAGES OF THE MORNING AND INTO THE AFTERNOON AS SURFACE TEMPERATURES RISE TOWARDS THE UPPER 70'S...FCST SOUNDINGS FOR THE REGION SHOW RELATIVELY LOW MLCAPE VALUES OF BETWEEN 200 AND 400J/KG...HOWEVER SBCAPE VALUES ARE LIKELY TO EXCEED 1000K/JG AND POSSIBLY REACH 1500J/KG WITH LI VALUES OF BETWEEN -2 AND -4C...THE UPPER LEVEL JET IN ASSOCIATION WITH THE LONG WAVE TROUGH OVER THE BRITISH ILSES WILL AID DEEP LAYER SHEAR OVER CENTRAL/N=ERN GERMANY & INTO S=ERN DENMARK...0-6KM SHEAR VALUES OF BETWEEN 40 AND 60KT ARE POSSIBLE ALONG WITH SOME LIMITED LOW LEVEL SHEAR (0-1KM 15-20KT)...FCST 0-3KM S-RH VALUES OF BETWEEN 160 AND 170M2/S2 & VGP VALUES OF 0.2 AND 0.25 WOULD ALLOW FOR SUPERCELL DEVELOPMENT IF THE FULL AVAILABLE CAPE IS USED...THE MLCAPE (LOWEST 50HPA MEAN) VALUES DO LIMIT THE OVERAL RISK OF SUPERCELL DEVELOPMENT TO A MORE MULTICELL OUTCOME...HOWEVER THE SBCAPE ALONG WITH THE ABOVE VARIABLES WOULD ALLOW FOR SUPERCELL DEVELOPMENT OVER N=ERN REGIONS OF GERMANY & INTO S=ERN DENMARK TOWARDS THE LATTER STAGES OF THE AFTERNOON...WBZ HEIGHTS OF BETWEEN 7000 AND 8000FT ALONG WITH THE AFOREMENTIONED INDICIES WOULD ALLOW FOR LARGE HAIL & LARGE RAINFALL TOTALS...TORNADOES ARE POSSIBLE OVER N=ERN GERMANY AND INTO S=ERN DENMARK, BUT AGAIN THIS WILL BE SOMEWHAT RELIANT ON THE AMOUNT OF CAPE USED DURING THE COURSE OF THE AFTERNOON...CONVECTIVE ACTIVITY IS LIKELY TO PERSIST DURING THE LATTER STAGES OF THE FCST TIME PERIOD, ESPECIALLY IF ANY SUPERCELL DEVELOPMENT HAS OCCURED. A MDT RISK MAYBE NECESSARY/ISSUED FOR PARTS OF N=ERN GERMANY/S=ERN DENMARK TOMORROW (SATURDAY) AFTERNOON IF MORE SEVERE DEVELOPMENT OCCURS.

...REST OF EUROPE EXCEPT MENTIONED LOCATIONS......
AN UNSTABLE CYLONIC NW=LY AIRFLOW WILL COVER THE MAJORITY OF THE BRITISH ILSES AND SCANDINAVIA BRINGING THE RISK OF DIRUNAL CONVECTIVE ACTIVITY...TSTSM DEVELOPMENT IS NOT EXPECTED TO BE WIDESPREAD & A GRADUAL REDUCTION IN ACTIVITY OVER W=ERN BRITIAN IS EXPECTED IN ASSOCIATION WITH THE WEAKNING 500MB TROUGH AND AN E=WARD MOVING SURFACE TROUGH...SOME CELLS WILL PRODUCE SMALL HAIL, WEAK TO MODERATE SURFACE GUSTS AND TEMPORARY HEAVY RAINFALL...SE=ERN PARTS OF SPAIN MAY SEE SOME ISOLATED TSTSM DEVELOPMENT DURING THE LATTER STAGES OF THE DAY IN ASSOCIATION WITH HIGH SURFACE TEMPERATURES BUT A LARGE SURFACE TD DEPRESSION IS LIKELY TO LIMIT THE INSTABILITY WITHIN THIS REGION. ALL OTHER REGIONS WITHIN A GEN RISK WILL AGAIN SEE SOME DIURNAL CONVECTIVE DEVELOPMENT WITH SCT TSTSM DEVELOPMENT, HOWEVER THE MAJORITY OF THE DEVELOPED TSTSM SHOULD REMAIN BELOW SEVERE LIMITS AND ANY CONVECTION WILL DIMINISH TOWARDS AND ESPECIALLY AFTER SUNSET.

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