CONVECTIVE FORECAST
VALID 06Z WED 25/05 - 06Z THU 26/05 2005
ISSUED: 24/05 18:40Z
FORECASTER: DAHL

There is a slight risk of severe thunderstorms forecast across the eastern baltic States and extreme NW Russia.

There is a slight risk of severe thunderstorms forecast across the S Balkan States.

General thunderstorms are forecast across E Europe and extreme W Russia.

SYNOPSIS

WSWLY upper flow is stretching across the NRN and N-central portions of Europe ... with imbedded short-wave trough expected to cross the Baltic States and parts of extreme NW Russia on Wednesday. Large-scale upper flow regime will slowly back and intensify as vort maxima revolve about mean Atlantic long-wave trough. Upper vort max expected over the Ionian Sea by Wednesday 00Z and vort max over Turkey will merge ... and result in elongated upper low extending from the SE Mediterranean into the S Ukraine late in the period. Plume of weakly to moderately unstable air is covering most of E Europe and portions of W Russia ... with the main N/S baroclinic zone expected to be stretching from extreme NW Russia across the Belarus and E Poland into the central Balkans by Wednesday midday.

DISCUSSION

...E Baltic States ... Extreme NW Russia ... E Belarus ... central Ukraine...
Air mass over E Europe and W Russia will likely remain weakly capped with MLCAPEs again climbing into 1000 to 1500 J/kg range... locally maybe in excess of that ... and widespread TSTMS are again expected to develop along the synoptic-scale front in the early afternoon hours. Further TSTMS should occur farther E along mesoscale features like outflow boundaries left from Tuesday's convection. Baltic upper trough should be one focus for potentially severe convection ... though associated strong deep-shear regime appears to remain somewhat displaced from the CAPE-bearing air mass.

However ... 500 hPa flow should be in the 15 to 20 m/s range over the Baltic States and portions of the Belarus ... with 850 hPa flow increasing towards NW Russia. Short convective lines with embedded mesocyclones may occur ... capable of producing damaging winds ... large hail and maybe a brief tornado. Upscale growth into one or more MCSs towards the evening hours is possible again.

Farther south ... Large-scale shear and forcing for ascent should be quite weak ... limiting severe TSTM threat. However ... as capping is weak and numerous cells may develop ... cell interaction and interaction with residual outflow boundaries may locally create environments supportive of brief severe TSTMS ... main threats being large hail and severe wind gusts ... though an isolated tornado cannot be ruled out especially late in the day and if deep/rich boundary-layer moisture is encountered. Severe threat is too conditional for a SLGT however.

...S Balkan States...
Low-level and deep-layer shear are expected to increase during the day ... with MM5 12Z assuming up to 20 m/s 850 hPa flow across the S Balkans. The high elevation may favor deeply mixed CBLs ... so that primary threats should be large hail and severe wind gusts. However ... rich boundary-layer moisture may be present locally ... especially over S Romania ... which may support an isolated tornado or two as well.

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