Storm Forecast
Valid: Mon 17 May 2010 06:00 to Tue 18 May 2010 06:00 UTC
Issued: Sun 16 May 2010 21:00
Forecaster: GROENEMEIJER

A level 1 was issued for the Baltic States, Eastern Poland, Belarus, the northern Ukraine, and a large part of west-central and southwestern Russia, mainly for large hail.

SYNOPSIS

A large vertically-stacked low remains almost stationary over the western Ukraine. Between this system and a high pressure area across northern Russia and the Polar Sea, warm and unstable air is advected westward, north of a poorly defined cold front that stretches from west-central Belarus across the NE Ukraine towards the Caucasus Mountains. On its western flank, a strong low-level flow transports cold air southward across central parts of Europe. Where the two flows meet, basically across Poland, Slovakia, and Hungary, heavy non-convective rainfall is expected.

Further south, an upper-level vorticity maximum moves eastward during the forecast period: across southern Italy, the Ionean Sea, Greece and into Turkey. Another upper-level vorticity maximum affects the Benelux, N France and Germany. Both upper-level systems are expected to produce deep convection with lightning.

DISCUSSION

Baltic States, northern Belarus and a large part of west-central and southwestern Russia...

Within the aforementioned warm and unstable air, diurnally driven thunderstorms are expected. Given that CAPE should values in the 1000-1500 range, isolated large hail is forecast. Because the boundary layer should be rather dry and deep in places, a couple of strong but mostly non-severe wind gusts are expected as well. Near the cold front and near the low's centre, convective forcing by the diurnal cycle will be augmented by that caused by a upper tropopspheric PV maximum that travels westward from the north-central Ukraine from 12 UTC onward. Regardless, convective activity should be widespread near the low's centre despite lower surface temperatures: numerous storms, some accompanied by large hail are expected. Where storms move slowly, very high rainfall accumulations may occur.

Northern Scandinavia...

This region lies within the easterly flow of relatively warm and unstable air, which is not particularly humid. Somewhat lower amounts of instability are expected here than further east, mostly in the 500-1000 J/kg range, which renders the severe threat quite low. Still, some mostly sub-severe hail and strong wind gusts are possible with diurnally-driven thunderstorms.

Western Turkey and eastern Aegean Sea...

Upon the approach of an upper-level vorticity maximum, rather widespread storms are expected to develop during the night. Limtied amounts of CAPE and wind shear suggest their severe threat will be rather low.