CONVECTIVE FORECAST
VALID 06Z MON 09/06 - 06Z TUE 10/06 2003
ISSUED: 09/06 02:27Z
FORECASTER: VAN DER VELDE

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SOUTHWESTERN FRANCE

GENERAL THUNDERSTORMS ARE FORECAST ACROSS ITALY, SOUTHERN & EASTERN EUROPE, BELARUS

GENERAL THUNDERSTORMS ARE FORECAST ACROSS NORTHERN DENMARK, SOUTHERN SWEDEN

SYNOPSIS

IN A MEANDERING SOUTHWESTERLY 500 HPA FLOW, A SURFACE LOW OVER SCANDINAVIA WILL TRANSLATE FURTHER NORTHEASTWARD. ASSOCIATED COLD FRONT PUSHING INTO HIGH THETA-W OVER 20 DEGREES AIRMASS, GENERATES EXTENSIVE CLOUDINESS FROM MCS ANVILS AT 00Z OVER SWEDEN INTO POLAND. DESPITE WEAKENING DYNAMICS BY SLIGHTLY BUILDING HIGH PRESSURE OVER THE CONTINENT, THE COLD FRONT WILL REMAIN A SOURCE OF THUNDERSTORMS DURING THE FCST PERIOD, MAINLY AFFECTING A LINE FROM THE ALPS INTO EASTERN POLAND. DURING THE AFTERNOON, A THERMAL LOW WILL FORM AT THE SIDE OF THE LONG 500 HPA WAVE SLOWLY APPROACHING FROM THE ATLANTIC. THIS FEATURE IS EXPECTED TO BE IN CENTRAL/NORTHERN FRANCE BY THE END OF THE FCST PERIOD.

DISCUSSION

...SLIGHT RISK AREA...
THERMAL LOW DEVELOPING DURING MONDAY AFTERNOON OVER SW-FRANCE WILL INGEST MOSTURE FROM THE MEDITERRENEAN SEA WHILE RISING MOTIONS ASSOCIATED WITH THE APPROACHING UPPER AIR TROUGH WILL LIKELY DESTABILIZE THE ATMOSPHERE ENOUGH FOR THUNDERSTORMS TO FORM... GFS 12Z INDICATES OVER 1000 J/KG MLCAPE_30HPA. DUE TO INCREASING DEEP LAYER SHEAR ...0-6KM 30-40 KTS, BRNSHEAR HIGHER THAN 40 M2S2... THESE STORMS COULD ORGANISE THEMSELVES INTO A MCS... HELPED BY COLD POOL FORMATION BECAUSE OF VERY DRY AIR ALOFT, ALREADY PRESENT IN 12Z PREVIOUS DAY BORDEAUX SOUNDING AND 00Z SANTANDER. RELATIVELY HIGH SR HELICITIES OF AROUND 200 M2/S2 FORECAST BY 12Z GFS IN COMBINATION WITH CAPE SUGGEST THAT A FEW SUPERCELLS SEEM LIKELY, PERHAPS EMBEDDED WITHIN THE MCS. DEVELOPING HIGH PRESSURE NEAR THE ALPS AS INDICATED BY PREVIOUS DAY 12Z GFS SUGGESTS INCREASED LIKELYHOOD THAT A LOW-LEVEL JET MAY FORM DURING NIGHTFALL AND CONTINUOUSLY SUPPLIES THE MCS WITH HIGH MOISTURE/TEMPS WHILE ON ITS WAY TO THE BENELUX COUNTRIES BY THE END OF THE FCST PERIOD, ALTHOUGH GFS 12Z CAPE´S ARE NOT TOO HIGH. SEVERE OUTFLOW WINDS AS ANTICIPATED STORMS ORGANISE INTO A MCS/SQUALL LINE ARE THE MAIN THREAT AND ALSO SOME LARGE HAIL.

...ITALY, WESTERN BALKAN INTO EASTERN EUROPE...
LIKE THE PREVIOUS DAY, SURFACE CONVERGENCE AREAS MOSTLY CAUSED BY SEA BREEZES (GFS ALSO FORECASTS CONV/DIV PATTERNS WELL) ALONG THE ITALIAN PENINSULA AND FORMER YUGOSLAVIA WILL BE THE MAIN TRIGGERING FACTORS WHILE CAPE OF 1500-2000 J/KG ARE ALSO PRESENT TODAY, AS THE SAME VALUES BY THE GFS MODEL YESTERDAY WERE CONFIRMED BY THE SOUNDINGS. ISOLATED LARGE HAIL AND WIND EVENTS ARE POSSIBLE, ESPECIALLY WHERE STORMS MAY GROUP TOGETHER, POSSIBLY UNDER INFLUENCE OF LARGER WIND SHEAR IN SOUTHERN ITALY, NEAR A SLACK UPPER LOW. HERE IS ALSO THE 18/00Z BRINDISI SOUNDING VERY UNSTABLE WITH MLCAPE OVER 1000 J/KG. ...WESTERN BALKAN AWAY FROM THE COAST MAY SEE MOST ACTIVITY IN MOUNTAINOUS REGIONS, OTHERWISE ISOLATED AND UNDER WEAK SHEAR CIRCUMSTANCES. 00Z BUDAPEST SOUNDING JUST AHEAD OF A MCS SHOWS 1200 J/KG 50 HPA-MLCAPE WITH NO CAP, 00Z ZAGRES EVEN 1600 J/KG WITH VERY DRY MIDLEVELS... ENOUGH TO FUEL THE APPROACHING MCS AT THE COLD FRONT INTO THE MORNING ....THIS COULD ASK FOR AN UPGRADE TO SLGT FOR WIND THREAT. ...00Z SOUNDINGS IN POLAND DO NOT LOOK IMPRESSIVE, HOWEVER IN SLOWAKIA, A SOUNDING AHEAD OF THE COLD FRONT INDICATES AMPLE INSTABILITY, HOWEVER WITH HIGH LFC AND WEAK SHEAR. THE ENVIRONMENT AHEAD OF THE COLD FRONT IN THESE LOCATIONS THEREFORE SEEMS FAVORABLE FOR MULTICELL STORMS THAT COULD LOOSE ITS LINEAR CHARACTER BECAUSE OF LESSER SHEAR AND WEAKENING THETA-E GRADIENTS. HOWEVER, THE OUTFLOW POOL COULD BECOME THE MAIN LINEAR TRIGGERING FACTOR. WEAKER PRESSURE GRADIENTS WILL ALSO LIMIT THE THREAT OF SEVERE GUSTS.

...SWEDEN...
MOIST, WEAKLY UNSTABLE PROFILES COULD GENERATE SOME THUNDER NEAR THE LOW PRESSURE CENTER. SOME FUNNELS/SPOUTS CANNOT BE RULED OUT GIVEN THE TYPICAL HIGHLY CYCLONIC FLOW AND LOW LFC`S, PROVIDED THAT SUFFICIENTLY DEEP CONVECTION CAN BE MAINTAINED.

#