CONVECTIVE FORECAST
VALID Tue 23 Aug 06:00 - Wed 24 Aug 06:00 2005 (UTC)
ISSUED: 22 Aug 23:52 (UTC)
FORECASTER: VAN DER VELDE

There is a slight risk of severe thunderstorms forecast across Romania, Bulgaria, northern Greece and eastern Bosnia/Serbia/Macedonia

SYNOPSIS

A mid/upper level cut-off low slowly tracks northeastward. Warm theta-e plume is advected northward at its east side, this creates most active convection there. At its south side, an upper jet reaches into the southeastern Balkan, providing sustained support for organized convection.

DISCUSSION

...southeastern Balkan...
Deep layer shear over the area reaches 15-22 m/s 0-6 km, being sufficient to support storms with a long-lived updraft and possibly rotation, although GFS/NMM model SREH and low-level shear forecasts are modest. Lower level temperature lapse rates have proven to be very steep in 12Z soundings, creating rapid ascent (good for marginally large hail and enhancing tornado chances). MLCAPE is on mostly the order of 300-800 J/kg, especially enhanced in the clear region ahead of the storms inside the warm theta-e plume. Supercell and organized multicell complexes may form, with large hail, an isolated tornado (or spout, by vortext-stretching) and some severe gusts can be expected. Aside from that, storms can move slowly or trail in the same area, producing locally large cumulative amounts of precipitation and possibly flash floods.

...area under the upper low...
The cold airmass creates steep temperature lapse rates in the boundary layer to midlevels over warmer surfaces. Convection in the merry-go-round is able to produce spout-type tornadoes in weak shear conditions and strong 0-3 km CAPE that will promote undisturbed upright stretching processes, especially in the presence of pre-existing convergence/vorticity lines. Additionally, slow motion of storms can provoke flash floods.

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