CONVECTIVE FORECAST
VALID 06Z SAT 11/09 - 06Z SUN 12/09 2004
ISSUED: 10/09 19:04Z
FORECASTER: DAHL

There is a slight risk of severe thunderstorms forecast across France ... S Benelux ... W Germany ... W Switzerland.

General thunderstorms are forecast across SW ... central and NE Europe.

SYNOPSIS

Vigorous upper vort max currently over the Atlantic ... is progged to migrate eastward ... reaching western and central Europe late on Saturday/early Sunday morning. Weaker vort max downstream should move from NRN Germany across the Baltic States into NW Russia during the period. At low levels ... plume of subtropical air mass is progged to continue spreading eastwards ... extending from the Baltic States across E-central Europe into the W Mediterranean by the end of the FCST period.

DISCUSSION

...NE-central Europe ...
Uncertainty exists with respect to the degree of instability of the air mass over France on Friday ... which will spread northeastward into NE-central Europe during Saturday. However ... indications are that at least weak instability will be present and thunderstorms will likely redevelop over Germany ahead of weak vort max and move across Poland into the Baltic States.

...France...
As UVV's ahead of strong downstream trough overspread the E edge of the weakly unstable air mass ... widespread convection may develop over France ... and move northeastwards into Switzerland ... W Germany and the S Benelux States towards late Saturday evening/night.

Strong large-scale ascent and about 20 m/s deep-layer shear will likely favor one or more lines of TSTMS with embedded bow echoes and supercells. Though the main threat will likely be severe straight-line winds ... a few large-hail events and maybe a brief tornado or two cannot be excluded. Severe threat may last well into late Saturday night given strong large-scale forcing.

...E Spain...
It looks that the air mass will be increasingly capped towards S and E France ... as well as over E Spain as indicated by BOLAM's 850 theta-e fields as well as Friday's soundings from E Spain. Also ... CAPE may be somewhat stronger there ... on the order of 1000 to 1500 J/kg. This may hint at more isolated development which should quickly become severe given the anticipated favorable thermodynamic and shear profiles. However ... degree of CAPE remains uncertain ... also ... UVV's are expected to weaken towards Spain ... and later OBS will have to be awaited to specify convective threat.

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