VALID 00Z FRI 25/10 - 00Z SUN 27/10 2002
ISSUED: 25/10 21:23Z
FORECASTER: DAHL

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF CNTRL EUROPE AND THE W BRTISH ISLES.

GENERAL THUNDERSTORMS ARE FORECAST ACROSS THE BRITISH ISLES...CNTRL AND ERN EUROPE.

SYNOPSIS

FAST ZONAL UPPER FLOW STRETCHING ACTROSS CNTRL EUROPE...PROMINENT FEATURES ON SATURDAY WILL BE TWO RAPIDLY EASTWARD SHIFTING VORT MAXIMA...WHICH ARE EXPECTED TO BE LOCATED OVER N GERMANY AND NEAR 30W OVER THE ATLANTIC RESPECTIVELY ON SATURDAY MORNING. STRONG CYCLOGENESIS UNDERWAY AHEAD OF THE ATLANTIC VORT MAX...WHICH WILL LIKELY AFFECT THE W BRITISH ISLES TOWARDS THE END OF DAY 2 PERIOD. DEEP POLAR AIR MASS IS EXPECTED TO SPREAD ACROSS ALL OF CNTRL AND PARTS OF EASTERN EUROPE...WITH THE ASSOCIATED COLD FRONT EXTENDING FROM THE N BALKAN SEA ACROSS W RUSSIA INTO THE BLACK SEA BY SUNDAY 00Z.

DISCUSSION

...CNTRL EUROPE...
AVN VORTICITY ADVECTION FCST'S SUGGEST SEVERAL RATHER SMALL-SCALE CVA MAXIMA ACROSS CNTRL EUROPE IN THE POSTFRONTAL ENVIRONMENT ON SATURDAY...WHICH SHOULD BE THE LOCATION OF DEEPEST CONVECTIVE MIXING. EXPECT BANDS OF ENHANCED CUMULUS CLOUDS AND/OR COMMA CLOUDS TO DEVELOP IN THE VICINITY OF THE CVA REGIMES. SHEAR IN THE CLOUD-BEARING LAYER IS EXPECTED TO BE ON THE ORDER OF 100 KNOTS...WHILE LAPSE RATES ARE EXPECTED TO BE NEUTRAL TO WEAKLY UNSTABLE. HOWEVER...ANY SHOWER/TSTM IN THIS ENVIRONMENT WILL AUGMENT STRONG GRADIENT WINDS AT THE SFC THROUGH VERTICAL MOMENTUM TRANSFER.. ESPECIALLY IF TSTMS BECOME LINEARLY ALLIGNED. ISOLATED WIND GUSTS ON THE ORDER OF 60 TO 70 KNOTS APPEAR LIKELY. ALSO...VERY LARGE HODOGRAPHS MAY FAVOR A FEW ROTATING UPDRAFTS...EITHER IF SRH IS CREATED AFTER STORM SPLITTING/DEVIANT MOTION OF THE CELLS OR IF OROGRAPHY ALTERS LOW-LEVEL WINDS SUCH THAT VEERING SHEAR VECTORS ARE PRODUCED IN THE LOWEST KILOMETER. THIS RESULTS IN SLIGHTLY ENHANCED CHANCES OF MARGINALLY SEVERE HAIL AND MAYBE A BRIEF TORNADO. HOWEVER...PRIMARY THREAT ON SATURDAY IS AUGMENTATION BY THE CONVECTIVE LINES OF THE STRONG LARGE-SCALE SFC FLOW.

...W BRITISH ISLES...
SIMILAR SITUATION WILL DEVELOP FARTHER WEST WITH THE NEXT SFC LOW... RISK OF SVR TSTMS OVER THE W BRITISH ISLES WILL LARGLY DEPEND ON EXACT TIMING OF THAT FEATURE.

......
OTHERWISE...CHANCES OF TSTM DEVELOPMENT ARE QUITE LOW.

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