CONVECTIVE FORECAST
VALID 06Z THU 22/05 - 06Z FRI 23/05 2003
ISSUED: 21/05 15:26Z
FORECASTER: GATZEN

GENERAL THUNDERSTORMS ARE FORECAST ACROSS SOUTHEASTERN EUROPE

GENERAL THUNDERSTORMS ARE FORECAST ACROSS EASTERN EUROPE

GENERAL THUNDERSTORMS ARE FORECAST ACROSS SPAIN

SYNOPSIS

SLIGHTLY NEGATIVELY TILTED TROUGH OVER CENTRAL EUROPE CUTS OFF AND DIGGS SOUTHEASTWARD INTO EASTERN MEDITERRANEAN. NORTHERN PART OF THIS UPPER TROUGH IS FORECAST TO MIGRATE EASTWARD. UPPER RIDGE OVER NORTHEASTERN ATLANTIC EXTENDS INTO CENTRAL EUROPE. AT THE SURFACE ... FRONTAL BOUNDARY OVER EASTERN EUROPE REMAINS QUASISTATIONARY. INTENSE SURFACE LOW IS EXPECTED NORTH OF THE BRITISH ISLES.

DISCUSSION

...SOUTHEASTERN EUROPE...
CUT-OFF LOW IS EXPECTED OVER THE REGION ... AND 500 HPA TEMPERATURE SHOULD REACH <-20 C OVER GREECE THURSDAY EVENING. COLD-AIR ADVECTION AT LOWER LEVELS SHOULD REDUCE INSTABILITY SOMEHOW, AND MODELS SUGGEST LOW INSTABILITY WITHIN THE DAY. HOWEVER ... SHOWERS AND THUNDERSTORMS WILL LIKELY DEVELOP IN THE RANGE OF UPPER TROUGH AND EAST OF IT WITHIN WARM AIRMASS OVER TURKEY. INCREASING 0-6 KM VERTICAL WINDSHEAR SHOULD ALLOW FOR SOME ORGANISED CONVECTION ESPECIALLY OVER TURKEY AND EASTERN GREECE. SOME HAIL AND STRONG WINDGUSTS SHOULD BE POSSIBLE.

...EASTERN EUROPE...
QUASISTATIONARY FRONTAL BOUNDARY ... SEPARATING UNSTABLE WARM AIRMASS EAST OF POLAND, HUNGARY AND THE BALKANS FROM COOL AIRMASS OVER CENTRAL EUROPE ... WILL BE THE FOCUS OF CONVECTION. MID-LEVEL DESCEND DUE TO CUT-OFF PROCESS SHOULD COUNTERACT CONVECTIVE ACTIVITY. HOWEVER ... ALONG WELL DEVELOPED SURFACE CONVERGENCE ... THUNDERSTORMS SHOULD FORM DURING THE DAY. EAST OF POLAND ... WEAK VERTICAL WINDSHEAR SHOULD NOT SUPPORT THUNDERSTORM ORGANIZATION. TO THE NORTH AND TO THE SOUTH ... VERTICAL SHEAR INCREASES GRADUALLY AND ORGANISED THUNDERSTORMS SHOULD BE MORE LIKELY. HAIL AND WIND GUSTS SHOULD BE THE MAIN SEVERE THREAT.

...SPAIN...
DAYTIME HEATING SHOULD ALLOW FOR SOME INSTABILITY. MODEL OUTPUT SUGGEST LARGE CIN AND THUNDERSTORMS ARE NOT LIKELY. HOWEVER ... IF SOME SHOWERS OR THUNDERSTORMS MAY FORM ALONG THE SEA BREEZE CONVERGENCE OVER SOUTHERN SPAIN ... SOME STRONG WINDGUSTS SHOULD BE POSSIBLE DUE TO WELL MIXED BOUNDARY LAYER.

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