CONVECTIVE FORECAST
VALID Sat 06 Aug 06:00 - Sun 07 Aug 06:00 2005 (UTC)
ISSUED: 05 Aug 21:50 (UTC)
FORECASTER: DAHL

There is a slight risk of severe thunderstorms forecast across the Baltic States ... stretching southwards into the Balkans and the Aegean Regions.

SYNOPSIS

Extensive upper low ... centered over the Nordic Sea by Friday late evening ... is progged to drop southwards ... becoming anchored over N-central Europe during Saturday ... featuring quite vigourous mid/upper flow ... and several vort maxima ... at its periphery. Meanwhile ... eastward moving upper cut-off low expected over Greece by Saturday 00Z ... will weaken and become increasingly integrated into circulation of the large central-European upper low. At low levels ... SFC low should develop in response to SWD shift of the upper system over S Scandinavia during the day ... with exact location and strength of this feature being somewhat incoherently forecasted by the various models. Over ERN portions of Europe ... quite moist and unstable air mass is present within plume stretching across the Aegean Regions ... Bulgaria ... Romania ... the Ukraine and the Belarus ... making some EWD progress as Scandinavian SFC low develops late in the day.

DISCUSSION

...Bulgaria ... Romania ... Aegean Regions...
Courtesy of the ELY flow over Romania and Bulgaria ... convective debris from Friday is quickly removed NEWD ... which should allow for unimpeded insolation across these regions on Saturday. It seems that deep CBL from Turkey is being advected across the SRN Black Sea ... and eventually across Romania and Bulgaria ... which should result in steepening lapse rates ... but also in increased CINH. Expect afternoon CAPEs in the 1000 to 2000 J/kg range with mixed-layer mixing ratios commonly in the 13 to 15 g/kg range.

Large-scale forcing for ascent is expected to be rather modest ... but mesoscale circulations e.g. associated with outflow boundaries laid out by Friday's convection ... and convergent SFC flow W of weak SFC low over the Black Sea and Turkey should provide sufficient low-level lift to initiate widespread TSTMS towards the afternoon hours.

Deep-layer shear should strongly depend on position relative to the weakening cut-off low ... and should be in the 15 to 20 m/s range at maximum based on MM5 wind fields. Though relatively modest on the large scale ... low-level shear will likely be rather strong locally by terrain and mesoscale circulations ... so that a few mesocyclones should be able to form. However ... dominating convective mode will likely be multicellular storms ... capable of producing large hail and damaging wind gusts. Especially with the supercells ... an isolated tornado or two may occur. Relatively weak back-ground shear across Bulgaria and Romania precludes more emphatic outlook at this time ... though an upgrade to MDT may be necessary with later outlooks.



...W Belarus ... S Baltic States...
Indications based on quite sparse sounding and SFC OBS data ... are that CAPE will decrease towards the north ... which is backed up by numerical-model guidance. However ... deep-layer shear of 20 to 25 m/s ... should be supportive to short line segments and possibly a few bow echoes and mesocyclones ... capable of producing some hail ... damaging winds and possibly a brief tornado or two.

...north-central Europe and S Scandinavia...
In the deep polar air beneath the N-central-European upper low ... numerous showers and TSTMS should develop with diurnal heating. As is typical for this type of convection ... strongest shear at the periphery of the upper cyclone will remain somewhat offset from the deeply convecting polar air mass. So ... shear should be somewhat marginal for severe evolution though a few shallow/short-lived mesocyclones ... capable of producing marginally severe hail and strong/severe wind gusts ... may be possible. Also ... a brief/weak tornado or two could occur ... though these may as well be associated with non-mesocyclonic storms ... especially over the Baltic-Sea region close to the low's center where shear should be minimal. Allower severe threat does not warrant a SLGT however.

#