Storm Forecast
Valid: Mon 07 May 2007 06:00 to Tue 08 May 2007 06:00 UTC
Issued: Sun 06 May 2007 21:50
Forecaster: GROENEMEIJER

DISCUSSION

Ukraine, Romania, Bulgaria, F.Y.R. of Macedonia...

Monday morning, a cold front should stretch southward over the western Ukraine, western Romania to Albania. Storms are expected along and ahead of the front. They will likely increase in coverage during the late morning and afternoon in response to solar heating and ahead of a minor shortwave. Most storms are expected over the F.Y.R. of Macedonia, west Bulgaria and west and north Romania and west Ukraine. Steep lapse rates are expected ahead of the front in the 900-750 hPa layer, inducing strong updraft speeds just above the freezing level, which will favour large hail formation. This together with deep-layer shear of around 10-15 m/s should be sufficient for organized multicells to form with a main threat of large hail.
A non-supercell tornado or two cannot be excluded either as low cloud bases, a lowering LFC and a surface wind field with cyclonic vorticity are is expected in the front's vicinity.
The front and the storm area should move eastward during the afternoon and evening. The severe threat and overall convective activity should gradually diminish after sunset.

Netherlands, Belgium, N Germany, W Poland...

A vigorous zonal jet stretching from the Atlantic over southern England should move eastward over the mentioned areas during the period while frontogenesis takes place. Strong wind shear is expected in the range of the jet/front system, but only weak cyclogenesis is expected in the left-exit quadrant of the jet per latest model guidance. As a result, the familiar pattern of ascending dry mid-tropospheric air atop moist low-level air resulting from the indirect circulation will not be very pronounced in the forecast period, leading to a lack of instability. A significant convective severe weather threat is therefore not expected. During the second half of the period some storms producing strong gusts may however develop over the aforementioned areas.