Storm Forecast
Valid: Thu 03 Aug 2006 06:00 to Fri 04 Aug 2006 06:00 UTC
Issued: Wed 02 Aug 2006 15:38
Forecaster: DAHL

SYNOPSIS

Vigorous and large upper low ... over central Europe on Wednesday afternoon ... is progged to slowly dig southeastwards ... resulting in deep and intense SWLY flow over the central Mediterranean and E Europe. Ahead of this feature ... quite warm/moist ... but only weakly/moderately unstable air mass is present ... with weak wave cyclones expected to develop along the associated cold-frontal boundary which should extend from central Spain across the NW Mediterranean into NE Europe by late Thursday night.

DISCUSSION

Italy ... north Balkans

Rather weak lapse rates across the Mediterranean and E Europe have precluded the built-up of large CAPEs despite rather rich LL moisture. Current thinking is that CAPEs will likely not exceed 1000 J/kg. However ... DLS should increase toward the afternoon hours over N Italy and the N Balkans ... as well as over the W Mediterranean. Given minimal capping and strong UVVs ahead of the approaching upper trough ... rather widespread convective storms should develop ... which may limit overall degree of organization of the TSTMS. Expect several MCSs to form ... which may account for large hail and severe wind gusts. Imbedded mesocyclones may augment the hail threat. Weak LL capping and increasing LLS suggest that a tornado or two could form as well. ATTM it seems that CAPE will be quite weak where shear will be maximized ... and will thus only introduce a level-one threat. Should CAPE turn out to be higher than currently anticipated ... an upgrade to level-two may be considered.

SE Poland

Northward-traveling frontal wave is expected to develop over the N Balkans and move into E Poland late in the evening/night. Shear profiles will be more than adequate for organized severe thunderstorms ... but degree of instability remains questionable. Also ... it seems that majority of the storms will be maintained in LL WAA regime and may thus tend to be elevated. However ... any SFC-based storm will have fair chances of becoming supercellular ... capable of producing the entire facet of severe weather ... including tornadoes owing to 10 and 15 m/s 0-1 km shear and low nocturnal LCL heights. Given the bad timing of the wave cyclone and associated uncertainties on effective instability available to the storms ... will only go with a level-one ATTM ... but an upgrade may be considered on Thursday.

central Europe

In the postfrontal environment over central Europe ... numerous small Cb's should form with diurnal heating. Though shear is expected to be rather marginal ... a brief/small tornado cannot be ruled out given low LCL heights and no capping. Waterspouts may occur over the Baltic Sea. However ... threat is too low for a categorical outlook.