CONVECTIVE FORECAST
VALID 12Z SUN 25/05 - 06Z MON 26/05 2003
ISSUED: 25/05 12:40Z
FORECASTER: VAN DER VELDE
GENERAL THUNDERSTORMS ARE FORECAST ACROSS MOST OF CENTRAL-EASTERN EUROPE, SOUTHEASTERN EUROPE, TURKEY
GENERAL THUNDERSTORMS ARE FORECAST ACROSS SOUTHERN SWEDEN
SYNOPSIS
AN NORTH-SOUTH ELONGATED UPPER TROUGH REMAINS ALMOST STATIONARY OVER THE UK/BENELUX INTO FRANCE AND SPAIN, WHILE HIGH PRESSURE BUILDS UP EASTWARD UNDERNEATH. THIS WILL CONNECT WITH THE HIGH PRESSURE AREA OVER RUSSIA AT THE END OF THE FCST PERIOD. A COLD FRONT OVER WESTERN SWEDEN INTO GERMANY INTO ITALY MARKS THE WESTERN BOUNDARY OF HIGH THETA-W BOUNDARY LAYER AIR (18 DEGREES ACCORDING TO GFS AT 18Z), WHILE SHALLOW LOW PRESSURE AND WEAK FORCING IS PRESENT OVER MUCH OF SOUTHEASTERN EUROPE, WITH ITS CORE OVER ROMANIA/BALKAN COUNTRIES INTO GREECE AND TURKEY, WHERE LOWER SFC THETA-W'S ARE PRESENT BUT COLDER UPPER AIR. MOST SHEAR IS PRESENT UNDER THE JETSTREAM OVER THE COLD FRONT, ON WHICH THE AIR IS JUST MARGINALLY UNSTABLE.
DISCUSSION
...MOST OF CENTRAL-EASTERN EUROPE, SOUTHEASTERN EUROPE, TURKEY...
GFS 00Z INDICATED CAPE VALUES REACH OVER THE 1000 J/KG NUMBER OVER ERN GERMANY, CZECH REPUBLIC, POLAND, BELARUS INTO ROMANIA AND FORMER YUGOSLAVIA. MOST 00Z SOUNDINGS IN THIS AREA DO NOT SEEM TO BE QUITE AS UNSTABLE, BUT WITH THE CURRENTLY OBSERVED SURFACE DEWPOINTS OF 17 DEGREES WITH TEMPERATURES OF 27 DEGREES, MOST LOCATIONS IN EASTERN EUROPE SHOULD ALLOW TSTM DEVELOPMENT. INSOLATION IS PRESENT ALL OVER THE AREA. HOWEVER -- A WELL DEFINED SOURCE OF UPWARD MOTION TO TRIGGER TSTMS IS HARD TO FIND... THE COLD FRONT OVER CENTRAL GERMANY COULD PROVIDE LIFT BUT WITH CURRENT 11Z DEWPOINTS OF ONLY 12-14 DEGREES APPLIED TO THE 00Z SOUNDINGS WITH WARM MIDLEVELS AND DRY BOUNDARY LAYERS, THIS IS A MARGINAL CHANCE. ONLY SOME ISOLATED THUNDERSTORMS ARE ANTICIPATED OVER EASTERN GERMANY. SHEAR PROFILES PRESENT IN THE 00Z BERGEN SOUNDING ARE EXPECTED TO HAVE LEFT THE AREA, AND WITH THE MARGINAL CAPE AS BASED ON CURRENT SURFACE OBS, NO SEVERE WEATHER IS ANTICIPATED.
...FARTHER EAST, IN EASTERN POLAND, BELARUS, WESTERN UKRAINE 00Z SOUNDINGS AND CURRENT SFC OBS LOOK GOOD FOR TSTMS, BUT SHEAR PROFILES SEEM TO BE LACKING SUPPORT FOR ANY ORGANISED SEVERE WEATHER... AND CONVECTIVE INITIATION WILL BE LIMITED BY STABILIZING/DIVERGING EFFECT OF THE HIGH PRESSURE AREA PRESENT IN MID-LOW LEVELS. STRONG TO PERHAPS SEVERE OUTFLOW WINDS WOULD BE THE MAIN THREAT WITH THIS ISOLATED CONVECTION, ALONG WITH A CHANCE OF SEVERE HAIL. CURRENT 10Z VIS IMAGE SHOWS LARGE FIELD OF CUMULI APPARENTLY BELOW A CAPPING INVERSION.
...FARTHER SOUTH, IN ROMANIA, THE 00Z SOUNDING SEEMS VERY MOIST AND UNSTABLE WHILE SHEAR PROFILE IS GOOD ENOUGH FOR ORGANISED MULTICELL CONVECTION. THUNDER IS ALREADY REPORTED ATTM, AND THE CARPATS MOUNTAIN RIDGE COULD LOCALLY ENHANCE SHEAR SO THAT UPDRAFTS CAN BE QUITE VIGOROUS AND PERHAPS ROTATING, ENHANCING THE THREAT OF LARGE HAIL.
THE GREECE/TURKEY AREA IS AFFECTED BY AN UPPER DISTURBANCE VISIBLE ON WV IMAGERY AND IN THE FORM OF AN UPPER LOW PRESSURE AREA, AND 00Z SOUNDINGS INDICATE QUITE SOME INSTABILITY, WHILE 00Z GFS INDICATES AMPLE CONVERGENCE AND CYCLONIC AIRFLOW... CAPE UP TO 500 J/KG, VERY MOIST LOWER LEVELS IN VERY LOW SHEAR ENVIRONMENT... USUALLY SUPPORTIVE OF FUNNEL CLOUDS SOMETIMES TOUCHING DOWN AS WATER/LANDSPOUTS.
... THE REST OF THE AREA COULD SEE SOME ISOLATED CONVECTION, MOSTLY TRIGGERED IN MOUNTAINOUS REGIONS AS SYNOPTIC/MESOSCALE TRIGGERING IS WEAK. EXPECT A CHANCE OF ISOLATED LARGE HAIL AND ESPECIALLY FLASHFLOODING WITH SLOW MOVING STORMS UNDER THESE WEAK UPPER WIND/HIGH MOISTURE SITUATION (K INDEX MINUS LIFTED INDEX WELL OVER 30)
...SOUTHERN SWEDEN...
OVERNIGHT CONVECTION UNDER HIGH SHEAR/HELICITY HAS CEASED, BUT INSOLATION (11Z TEMPERATURES 24 DEGREES), SURFACE WIND CONVERGENCE INDICATED BY 00Z GFS. THE MODEL ALSO INDICATES SOME CAPE FOR 12/18Z BUT OVER A SMALL AREA. LATEST VIS SHOWS SIGNS OF REDEVELOPING CONVECTION WHILE 0-6 KM SHEAR IN WESTERN PARTS OF THIS AREA IS STILL EXPECTED TO REACH MORE THAN 40 KTS/> 40 M2S2 BRN SHEAR. 0-1 KM SHEAR IS BETTER NORTH OF THE AREA - BUT GFS REGULARLY UNDERSTIMATES 0-1 KM SHEAR. FAVORABLE CONDITIONS WILL EXIST FOR ONLY A SMALL AREA AND SEVERE THREAT IS NOT EXPECTED TO BE WIDESPREAD, SO I REFRAIN FROM ISSUING A SLGT RISK.
...UK, WESTERN FRANCE, BENELUX...
CONVECTION PRESENT OVER MUCH OF THE AREA, WHILE CAPE'S MAY NOT BE SUFFICIENT TO PRODUCE LIGHTNING AT ORGANISED SCALE, LOW LCL/LFC'S AND LOW LEVEL INSTABILITY AND MOISTURE IN LOW LEVEL WEAKLY SHEARED ENVIRONMENT BELOW THE UPPER TROUGH MAY GIVE RISE TO A FEW LAND/WATERSPOUTS, ESPECIALLY OVER ENGLAND WHERE SURFACE FLOW IS CYCLONIC AND THE 00Z CAMBORNE SOUNDING SHOWS SUPPORT FOR VIGOROUS SHALLOW CONVECTION. MORE CLUSTERED CONVECTION IS ONGOING OVER THE BENELUX WHERE 00Z SOUNDINGS WERE VERY MOIST, AT THE APPROACH OF THE UPPER TROUGH - HOWEVER, WIND CONDITIONS MAY BE TOO STRONG IN THESE LOCATIONS TO BE FAVORABLE FOR SPOUTS.
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