CONVECTIVE FORECAST
VALID 12Z SUN 11/05 - 06Z MON 12/05 2003
ISSUED: 11/05 13:06Z
FORECASTER: VAN DER VELDE

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SLOWAKIA, SE-POLAND, UKRAINE, HUNGARY, N-ROMANIA

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS CENTRAL ITALY

GENERAL THUNDERSTORMS ARE FORECAST ACROSS NORTHWESTERN PARTS OF THE BRITISH ISLES

GENERAL THUNDERSTORMS ARE FORECAST ACROSS EASTERN SPAIN

GENERAL THUNDERSTORMS ARE FORECAST ACROSS NORTHEASTERN SCANDINAVIA INTO RUSSIA

SYNOPSIS

LOW PRESSURE BETWEEN ICELAND AND SCOTLAND WITH ASSOCIATED CYCLONIC FLOW OVER THE BRITISH ISLES PROGRESSING INTO THE BENELUX. HIGH PRESSURE OVER THE BALTIC STATES, THE REST OF EUROPE IS UNDER LOW PRESSURE GRADIENTS. 500 HPA FLOW FROM SOUTHWESTERLY DIRECTIONS OVER MOST OF EUROPE WITH A TROUGH ENTERING WESTERN EUROPE INTO THE FORECAST PERIOD, WITH CYCLONIC 500 HPA FLOW SPREADING OVER EUROPE AS FAR SOUTHWARD AS SPAIN AND ITALY. CONVERGENCE ZONES IN HIGH THETA-W >16C OVER PORTIONS OF EASTERN EUROPE, ITALY AND SPAIN. A COLD FRONT ASSOCIATED WITH LOW LCL´S AND GRADUALLY DECRESING THETA-W´S AT THE BACK SIDE FROM POLAND INTO AUSTRIA REMAINS STATIONARY AND WEAKENING. THIS SETUP SHOULD LEAD TO LARGE SCALE TSTM ACTIVITY IN A REGIME WITHOUT LOCALIZED STRONG DYNAMICS.

DISCUSSION

...SLOWAKIA, SE-POLAND, UKRAINE, HUNGARY, N-ROMANIA...
GFS INDICATES AMPLE INSTABILITY ACROSS EASTERN EUROPE SOUTH AND WEST OF THE STATIONARY COLD FRONT. MODEL INDICATED CAPE´S COULD RISE INTO THE 1000-2000 J/KG NUMBER FROM ROMANIA INTO THE WRN UKRAINE (DEWPOINTS 16-18 DEGREES), WHERE ALSO SUFFICIENT SFC CONVERGENCE AND WEAK CAPS ARE PRESENT TO INITIATE STORMS. AS DEEP LAYER SHEAR IS MODERATE, AND 0-1 KM SHEAR SHOULD NOT BE LARGE (BELOW 15 KTS), MULTICELLS WITH A CHANCE OF PRIMARILY LARGE HAIL AND STRONG OUTFLOW GUSTS (DIFFERENCE BETWEEN SFC AND MINIMUM THETA-E AROUND 15-20 DEGREES PER GFS DATA). ...HOWEVER, SUPERCELLS ARE LIKELY TO FORM IN THE AREA IN THE ERN POLAND-WRN UKRAINE AREA AS STORM RELATIVE HELICITIES ARE PROGGED TO BE IN THE ORDER OF 100-300 M2/S2 IN MODERATE CAPE AREAS AND HAVE A HIGHER CHANCE OF SEVERE WEATHER, AGAIN WITH MOSTLY LARGE HAIL AND SEVERE GUSTS AS PRIMARY THREAT. A CHANCE OF AN ISOLATED TORNADO IS HIGHEST IN SRN POLAND IF A STORM MANAGES TO DEVELOP AT THE COLD FRONT WHERE LOW LCL´S ARE PRESENT.

...CENTRAL ITALY...
ELEVATED CONVECTION POSSIBLE AS INDICATED BY 06Z PRATICA SOUNDING WITH 00Z GFS INDICATING UP TO 1000 J/KG CAPE FOR 12Z/18Z... BY HEATING DURING THE DAY SFC BASED CONVECTION SHOULD BE POSSIBLE. 0-6 KM SHEAR OVER 40 KTS PRESENT IN MENTIONED 06Z SOUNDING SUGGESTS A CHANCE OF LARGE HAIL IS NOTABLE, ESPECIALLY OVER THE CENTRAL MOUNTAIN REGION. AMPLE SFC WIND CONVERGENCE (SEA BREEZE) AND 500 HPA TROUGH ABOVE SHOULD PROVIDE ENOUGH LIFT TO ALLOW CONVECTION.

...OTHER AREAS...
WHERE LOW LFC´S IN COMBINATION WITH LOW LEVEL INSTABILITY AND LOW SHEAR ENVIRONMENTS, THESE COULD LEAD TO ISOLATED LANDSPOUTS IN THE REMAINDER OF THE GEN TSTMS AREAS. HOWEVER GFS MODEL INDICATIONS ARE NOT TOO SURE ABOUT LFC HEIGHTS OVER TIME.

#