CONVECTIVE FORECAST
VALID 06Z MON 25/08 - 06Z TUE 26/08 2003
ISSUED: 24/08 18:40Z
FORECASTER: DAHL

There is a slight risk of severe thunderstorms forecast across the central Mediterranean.

General thunderstorms are forecast across S ... E and N Europe.

SYNOPSIS

As building upper ridge ATTM over the British Isles expands NWWD ... High-over-low block is expected to establish over the central Atlantic towards the end of the forecast period ... Quasi-stationary deep/extensive upper low with several vort maxima at its periphery is covering NE Europe. Weakly undulating zonal southern frontal zone is extending across the Mediterranean regions. At low levels ... Polar airmass is covering N and NE parts of Europe ... with the associated cold front stretching from N France across S Germany and the N Balkans into NW Russia where it will make some eastward progress ahead of NE European upper trough.

DISCUSSION

...S Europe...
Little change expected across the Iberia ... the Mediterranean ... and SE Europe. Majority of the soundings show very shallow low-level moisture and essentially inverted-V profiles. However ... indications are that SFC-based moist layer will be maintained locally ... supporting MLCAPEs up to 2000+ J/kg given very steep lapse rates extending up to about 550 hPa. BOLAM 850 hPa theta-e analyses suggest that another plume of well-lixed mixed desert air to advect across the central Mediterranean ... which may aid in trapping low-level moisture beneath the cap. Altogether ... thermodynamic profiles across the region are expected to be predominantly weakly unstable and of inverted-V type ... while locally rich low-level moisture could be present ... supporting strong CAPE values.

Today's 12Z wind profiles suggest that southern-stream vort maxima are accompanied by moderately strong mid-level winds ... yielding 0-6 km shear on the order of 30 to 40 knots. Storms that develop amidst this wind regime in inverted-V environs ... should pose some threat of damaging wind gusts ... and briefly organized lines of multicellular storms and maybe a bow echo or two may occur. Where 2000+ J/kg CAPE is realized ... threat of supercells will be greatly enhanced ... which would be capable of producing large hail along with damaging wind gusts. Large dewpoint depressions should keep CAPE density in the lowest kilometers rather low ... and tornado threat does not appear to be particularly high though small chances of a brief tornado will exist with any supercell that forms.

Storms should initiate primarily in response to DCVA-related lift ahead of the vort maxima ... orographic forcing along the Alpeninne mountains and insolation. Setup is fairly marginal ... and will place SLGTs where wind field is expected to be enhanced invof the vort maxima. Low probabilities for a brief severe-wind event exists across all of S Europe.

...NE Europe...
Shallow TSTMS may form ahead of vort maxima rotating about the main NE European upper low ... CAPE will be quite poor ... and despite decent vertical shear ... severe TSTMS appear to be unlikely. Expect small hail and strong wind gusts with the strongest cells though.

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