CONVECTIVE FORECAST
VALID 06Z SUN 27/04 - 06Z MON 28/04 2003
ISSUED: 27/04 03:06Z
FORECASTER: VAN DER VELDE
THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE BENELUX AND NW GERMANY
GENERAL THUNDERSTORMS ARE FORECAST ACROSS IRELAND, GREAT BRITAIN
GENERAL THUNDERSTORMS ARE FORECAST ACROSS CENTRAL SPAIN
GENERAL THUNDERSTORMS ARE FORECAST ACROSS CENTRAL ITALY
GENERAL THUNDERSTORMS ARE FORECAST ACROSS NW YUGOSLAVIA THROUGH SRN POLAND
SYNOPSIS
WAVE THAT DEVELOPED YESTERDAY OVER BENELUX AREA IS MOVING TO SRN SWEDEN. A COLD FRONT EXTENDS NORTH-SOUTH OVER ERN EUROPE. VERY LOW LCLS ASSOCIATED WITH THE CF BUT SHEAR AND INSTABILITY CONDITIONS ARE GENERALLY LESS THAN YESTERDAY. ....VARIOUS MODELS INDICATE LOW AMPLITUDE SHORT WAVES IN THE SURFACE FLOW UNDER THE JET OVER NRN FRANCE AND THE BENELUX AREA INTO GERMANY, FUNCTIONING AS THE MAIN TRIGGERS FOR CONVECTION, EVEN THOUGH INSTABILITY IS ONLY MARGINAL. UNSTABLE POLAR AIRMASS ALSO CIRCULATES OVER THE IRELAND AND GREAT BRITAIN AROUND THE SFC LOW NORTHWEST OF SCOTLAND. ....HIGHER PRESSURE IS SITUATED OVER THE MEDITERRENEAN WITH SOME MINOR DISTURBANCES OVER SPAIN AND ITALY.
DISCUSSION
...BENELUX AND NW GERMANY...
SAT 12Z GFS INDICATES CAPE VALUES UP TO 100 J/KG SUGGESTING SHOWERY CONDITIONS IN THE POLAR AIRMASS. INSTABILITY IS PROGGED TO BE HIGHEST TOWARDS THE NORTH, WHILE BOTH DEEP LAYER & LOW-LEVEL SHEAR SHOULD BE HIGHER TOWARDS THE SOUTH. UPWARD MOTIONS BY UPPER AIR VORTICITY ADVECTION ARE FORECAST THROUGHOUT THE RISK AREA. THE CAPE DISTRIBUTION SUGGESTS THAT THE SOUTHERN HALF OF THE BENELUX MAX SEE MORE STRATIFORM RAIN WHILE THE NORTHERN HALF A TENDENCY TO FORM MORE INTENSE SHOWERS, WITH A CHANCE OF WEAK ELECTRIFICATION. VERY LOW LCLS IN COMBINATION WITH 0-1 KM SHEAR OF >20 KTS ARE ONCE AGAIN IN PLACE AND POSE A THREAT OF A FEW DAMAGING TORNADOES AS WAS THE CASE YESTERDAY UNDER SIMILAR LCL/SHEAR CONDITIONS WITH CONSIDERABLE LOW LEVEL BUOYANCY. CURRENT 00Z SOUNDINGS IN THE AREA SHOW AGAIN VERY MOIST LAYERS UP TO 700 HPA AND VERIFY LOW LCLS AND POTENTIAL INSTABILITY, ALSO INDICATED BY SOME SHOWERS ON IR SATELLITE IMAGERY OVER THE NETHERLANDS AND FRANCE. ...MORE WIDESPREAD TODAY IS THE RISK OF STRONG OUTFLOW UP TO 45 KTS ASSOCIATED WITH THE MORE INTENSE AND MORE ORGANISED CONVECTION, POSSIBLY IN THE FORM OF LINES/BOW ECHOES. SMALL HAIL IS POSSIBLE WITH STRONGER CELLS.
...IRELAND, GREAT BRITAIN...
CAPES OVER 100 J/KG IN A CYCLONIC FLOW AROUND THE LOW NORTHWEST OF SCOTLAND SHOULD GENERATE NUMEROUS SHOWERS WITH SOME THUNDER, POSSIBLY OROGRAPHICALLY ENHANCED.
...NW YUGOSLAVIA THROUGH SRN POLAND...
CLEAR SPLIT-LEVEL CF AS ON 00Z IR IMAGERY WITH RISING MOTIONS COULD TRIGGER SOME WEAK TSTMS IN ELEVATED AREAS OVER ERN EUROPE. CONDITIONS MAY BE FAVORABLE FOR SOME SPOUTS IF LOW LEVEL BUOYANCY COULD DEVELOP. CLEAR AIR BEHIND THE CF ALLOWS INSOLATION WHICH MAY TRIGGER POSTFRONTAL SHOWERS WITH OCCASIONAL THUNDER, BUT HIGHER LCL/LFCS.
...CENTRAL SPAIN...
GFS MODEL INDICATES DEVELOPING SFC CONVERGENCE AND SOME CAPE IN A WEAK SYNOPTIC SETUP. A SMALL CHANCE THAT HIGH-BASED TSTMS DEVELOP IN THE AFTERNOON. NO PRECIP IS INDICATED BY THE 18Z GFS MODEL RUN HOWEVER, MIGHT BE AN INDICATION THAT CAPPING MAY BE TOO STRONG OR LIFTING MECHANISM TOO WEAK.
...CENTRAL ITALY...
INSTABILITY IS INDICATED BY THE GFS MODEL FOR 12Z, BUT THE MAIN POTENTIAL TRIGGER (UPPER TROUGH/BROKEN CF) HAS THEN ALREADY PASSED... HOWEVER OROGRAPHIC FEATURES OR A BAND OF PVA AS INDICATED BY GFS MAY INITIATE CONVECTION.
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