CONVECTIVE FORECAST
VALID 06Z SAT 14/08 - 06Z SUN 15/08 2004
ISSUED: 13/08 20:45Z
FORECASTER: DAHL

There is a slight risk of severe thunderstorms forecast across the S Balkans ... the E Ukraine and extreme W Russia.

General thunderstorms are forecast across portions of central Europe and the eastern half of Europe.

SYNOPSIS

Eastward moving upper cut-off low analyzed over central Europe on Friday evening is expected to phase and eventually merge with digging Scandinavian upper trough ... resulting in extensive long-wave trough covering E Europe and extreme W Russia by Saturday night. Upstream ... mid/upper ridging will spread into central and W Europe on Saturday ahead of large-scale upper cut-off low parked over the E Atlantic. At low levels ... fairly intense cyclogenesis over the Belarus and the Baltic States is accompanying eastward acceleration of the central European upper low ... moving into NW Russia by the end of the period. Plume of weakly unstable subtropical air mass will persist E of the E-European large-scale trough ... with modified polar air overspreading much of central and W Europe in its wake.

DISCUSSION

...SLGT area...
Soundings across E Europe reveal largely weak instability ... with MLCAPEs on the order of 500 J/kg. Latest SFC OBS indicate dewpoints in excess of 20°C over Romania and parts of Bulgaria ... suggesting that CAPE may be somewhat enhanced there. These inhomegeneities are expected to persist through Saturday across the S Balkans into the E Ukraine ... where locally MLCAPEs in the 1000 to 1500 range are expected. Farther N in the theta-e tongue ... CAPEs should generally be somewhat weaker.

Storms will likely (re-)develop amidst strong DCVA-related UVM regime progged to overspread the Balkan States during the day. Deep-layer shear will be on the order of 20 m/s which should be sufficient for a few rotating updrafts and bowing segements ... mainly posing a threat of large hail and damaging wind gusts. Storms may merge into a linear MCS ... but currently anticipated weak thermodynamic profiles preclude more emphatic risk category ATTM.

Further north ... shear profiles should improve substantially ... especially at low levels with 0-1 km SRH exceeding 150 m2/s2 ... and 0-3 km SRH exceeding 400 m2/s2. Though instability appears to be quite meager ... LCL heights are expected to be rather low ... altogether posing an additional threat for a few tornadoes. SLGT currently suffices given some uncertainty with respect to instability/convective development ... if convection turns out to be more widespread that currently anticipated ... a MDT will be required.

...SE-central Europe ... Benelux ... NW Germany...
Scattered showers ... and a few TSTMS ... will likely form with diurnal heating air over portions of central Europe ... aided by weak DCVA accompanying small-scale perturbations in the NLY flow at the W periphery of the E-European upper trough. GFS and NMM hint at a region extending from Benelux into the central Belarus ... and SE central Europe ... for deepest convective development. 850 hPa flow of 10 to 15 m/s is progged be in place ... supporting strong enough low-level shear profiles to be beneficial to an isolated shallow mesocycone or two. An isolated marginally severe wind/hail event and maybe a brief tornado may thus occur ... with the allover severe weather threat being too low for a categorical risk.

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