VALID 06Z WED 16/10 - 06Z THU 17/10 2002
ISSUED: 15/10 21:11Z
FORECASTER: GATZEN

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS NORTHWESTERN GERMANY

GENERAL THUNDERSTORMS ARE FORECAST ACROSS BENELUX/ NORTHERN FRANCE/ NORTH AND CENTRAL GERMANY

GENERAL THUNDERSTORMS ARE FORECAST ACROSS SOUTHERN FRANCE/ SPAIN

THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS WESTERN MEDITERRANEAN/ NORTHERN ITALY

SYNOPSIS

INTENSE LONG-WAVE-TROUGH OVER NORTHEASTERN ATLANTC PROPAGATING SLOWLY EASTWARD WILL REACH WESTERN EUROPE ON THURSDAY. TO THE EAST STRONG SOUTHWESTERLY FLOW AFFECTS MOST PARTS OF WESTERN/ CENTRAL EUROPE. INTENSE JET STREAK ROTATING ALONG THE EDGE OF ATLANTIC LONG-WAVE-TROUGH WILL CROSS MOST PARTS OF WESTERN EUROPE ON THURSDAY IN ADDITION WITH STRONG VORTICITY-ADVECTION WHILE ASSOCIATED SHORT-WAVE-TROUGH IS TILTING. AT THE SURFACE ... IN ASSOCIATION WITH HIGH THETA-E-ADVECTION ZYCLOGENESIS IS FORECASTED OVER WESTERN CENTRAL EUROPE AND SHOULD LEAD TO NEW STORM DEVELOPMENT WHICH PROBABLY WOULD REACH SEVERE LEVEL.

DISCUSSION

...SOUTHERN NORTH SEA AND SURROUNDING AREA/ SOUTHERN ENGLAND...
STRONG VORT MAX DISCRIBED ABOVE TRAVELS FROM THE BRETAGNE TO WESTERN GERMANY IN THE MORNING HOURS ... AND STRONG CYCLONAL VORTICITY ADVECTION WILL BE IN PLACE FROM THE BRETAGNE TO NORTHERN FRANCE, SOUTHERN ENGLAND, THE CHANNEL, SOUTHERN NORTH SEA, AND BENELUX. IN THE SAME TIME, RELATIVELY HIGH THETA-E WILL FLOOD NEARLY ENTIRE FRANCE AND SOUTHERN BENELUX WHILE FRONTAL BOUNDARY IS FORECASTED TO REMAIN JUST WEST OF THE CONTINENT, WHERE NEW FRONTAL WAVE IS FORMING. THIS WAVE IS FORECASTED TO DEEPEN RAPIDLY WHEN REACHING SOUTHERN SCANDINAVIA ON THURSDAY MORNING. DOWNSTREAM OF THAT WAVE VORT MAX WILL CROSS OLD FRONTAL BOUNDARY OVER SOUTHERN NORTH SEA BY WEDNESDAY MORNING ... AND NEW THUNDERSTORM DEVELOPMENT IS LIKELY. STRONG LOW LEVEL SHEAR ... WITH WEAK WINDS AT THE SURFACE AND STRONG SOUTHWESTERLY FLOW IN 850 HPA COULD HELP TO ORGANISE CONVECTION ... AND PROBABLY LOW-BASED SUPERCELLS COULD FORM ... HOWEVER ... CHANCE IS NOT VERY HIGH FOR ISOLATED CONVECTION THOUGH ... WHILE STRATIFORM PRECIPITATION-BAND COULD FORM ALONG FRONTAL BOUNDARY. IF THUNDERSTORMS OCCUR, SMALL HAIL/STRONG WIND GUSTS AND HEAVY RAINFALL SHOULD BE POSSIBLE ... AND ISOLATES WATERSPOUTS/ TORNADOS ... HOWEVER ... CHANCE IS TOO SMALL THAT ORGANISED STROMS WILL OCCUR TO WARRENT A SLIGHT RISK. BEST CHANCES FOR SEVERE CONVECTION SHOULD BE IN SOUTHERN ENGLANG, WHERE WATERSPOUTS ARE LIKELY. AT THE END OF THE FORECAST TIME, STRONG WINDS SHOULD OCCUR WEST OF THE NEW LOW. EVEN GIVEN STRONG NEGATIVLY THETA-E-ADVECTION SHOULD NOT MAKE SHOWERS UNLIKELY. STRONG WIND GUSTS SHOULD BE THE MAIN THREAT WITHIN THESE SHOWERS.

...BENELUX/ NORTHERN FRANCE/ NORTH AND CENTRAL GERMANY...
COLD FRONT OF NEW FRONTAL WAVE REACHES THE AREA IN THE AFTERNOON ... HOWEVER ... ASSOCIATED COLD AIR ADVECTION WILL BE VERY WEAK WHILE FRONTAL BOUNDARY WILL BE NEARLY PARALELL TO LOW-LEVEL FLOW. AS A CONSEQUENCE CONVECTIVE ACTIVITY SHOULD FORM AFTER MIDDAY ALONG THE FRONTAL BOUNDARY. GIVEN STRONG SHEAR PROFILES IN THE LOWER LEVELS ... TSTMS SHOULD BE ORGANISED ALONG THE FRONT. HEAVY RAINFALL, STRONG WIND GUSTS UP TO 50 KN, BIG HAIL AND A FEW TORNADOS SHOULD BE POSSIBLE ESPECIALLY OVER NORTHWESTERN GERMANY, WHERE OROGRAPHIE COULD ENHANCE SRH.

...SOUTHERN FRANCE/ SPAIN...
COLD FRONT WILL CROSS THE REGION TILL THURSDAY MORNING WITH NEGATIVE THETA-E-ADVECTION. UPPER TROUGH WILL PROPAGATE TO THE EAST IN ADDITION WITH CYCLONAL VORTICITY ADVECTION. ALONG THE FRONT ... SOME TSTMS COULD OCCUR ... HOWEVER ... CAPE SHOULD BE ZERO OR MARGINALLY, AND TSTMS SHOULD BE WEAK.

...SOUTHERN SCANDINAVIA...
AT THE END OF THE FORECAST PERIOD ... STRONG THETA-E-ADVECTION WILL AFFECT THE AREA ... WHILE COLD AIRMASS WILL REMAIN IN LOWER LEVELS. HEAVY PRECIPITATION ... ESPECIALLY AT HIGHER TERRAIN HEAVY SNOWFALL ... SHOULD OCCUR.

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