Storm Forecast
Valid: Mon 08 Jun 2009 06:00 to Tue 09 Jun 2009 06:00 UTC
Issued: Sun 07 Jun 2009 21:51
Forecaster: GROENEMEIJER

A level 2 was issued for parts of SW Russia, central Ukraine, parts of Moldova and Romania mainly for large hail, excessive rainfall, and to a lesser extent for wind gusts.

A level 1 was issued for a larger area including parts of Bulgaria, mainly for large hail, excessive rainfall, and to a lesser extent for wind gusts.

A level 1 was issued for parts of France mainly for tornadoes.

SYNOPSIS

Monday at 0600 UTC... a broad west to southwesterly jet stream is located over Europe. During the forecast period, a vorticity maximum over northern Germany and Denmark translates ENEward to the St. Petersburg area, and another vorticity maximum near Cape Finisterre translates to NWern France. Downstream of these features, a weak trough stretching from W Russia across Belarus to the central Balkans moves eastward rather slowly. The lower tropospheric temperature gradient across the jet is rather weak, with a well-defined elevated mixed layer only being present across the eastern Balkans and into the Ukraine

DISCUSSION

SW Russia, central Ukraine, Moldova, Romania, Bulgaria

Convergence ahead of the east-ward moving mid/upper-level trough causes moisture to pool under the elevated mixed layer that is in place across the eastern 1/3 of the Balkan Peninsula, and central parts of the Ukraine. The result is that substantial MLCAPE, up to around 2000 J/kg should develop as the moist air is diurnally warmed. Models suggest that convection will initiate in various places. Given that 0-3 km shear will be near 15 m/s, supercells will be possible, in addition to well-organized multicells. These will have a threat of producing large or even very large hail, and may also cause severe wind gusts. As storms will probably move mostly paralell to the low-level convergence zone, training of storm cells is probable, and excessive rainfall is warned for. Storms will weaken during the late evening and night.

France...

Ahead of the approaching vorticity maximum and an associated surface low over the Bay of Biscay, the south- to southwesterly low-level flow will intensify to around 15 m/s at 850 hPa. Scattered convective storms are expected to develop as a result of diurnal heating. A few factors favourable for (weak) tornadoes appear to become spatially and temporally collocated across the level 1 area. These are i) a moist low-level air-mass with forecast dew point temperatures around 14-15 C ii) the development of a W-E oriented warm front iiI) sufficient low-level and deep-layer shear for storm rotation. Together these factors appear to be sufficient for the issuance of a level 1, despite the fact that CAPE stays rather low. To put it shortly, a few tornadoes may occur, most likely near the warm front or other boundaries. Some small hail is possible too. The storms will quickly weaken after sunset.

Baltic States, NW Belarus...

Ahead of the vorticitiy maximum over northern Germany, which translates ENE-ward, some instabiltiy will probably form. Deep-layer and low-level may be marginally sufficient to support some updraught rotation. However, only a few storms are expected to form during daytime, and the shear is marginal enough for a level 1 for a tornado threat not to be required.