Storm Forecast
Valid: Wed 16 May 2012 06:00 to Thu 17 May 2012 06:00 UTC
Issued: Wed 16 May 2012 06:12
Forecaster: PUCIK

A level 1 was issued for NW Romania, W Ukraine, W Belarus, E Baltic States mainly for excessive precipitation.

A level 1 was issued for NE Ukraine, W Russia, E Belarus mainly for severe wind gusts, marginally large hail and to the lesser degree for tornadoes.

SYNOPSIS

A complicated synoptic setup is forecast over Europe during the forecast period. At mid and upper levels of troposphere, a negatively tilted trough will stretch from the Norwegian Sea into Central Europe and all the way to the Southeastern Mediterranean. Three separate centers with the most prominent one over Romania are simulated within the trough. Enhanced northwesterly flow between the trough and the ridge over Iberia will stimulate the amplification of the trough towards southeast. Trough is forecast to weaken especially over Central Europe as the ridge from Iberia spreads towards northwest. Another ridge over Eastern Europe will block the passage of the trough towards east.

Closer to the surface, a main frontal zone will strech from the Southeastern Mediterranean across Ukraine into the Baltic States with quickly advancing warm front towards Finland. Warm sector ahead of this wavy frontal boundary associated with broad low pressure system centered over Romania/Western Ukraine will be a focus for widespread DMC activity especially during the late afternoon and evening hours. A surface high will cover majority of Western Europe while a shallow surface low is expected to affect Iberia in the late evening/night hours.

DISCUSSION

... Northwestern Iberia ...

Models are in general disagreement regarding release of latent instability and also in the degree of convective initiation. Most of the NWP show almost no precip with very high CIN values associated with very warm temperatures in the low levels of troposphere. Strong cap will likely limit any thunderstorm development in the warm sector in the environment of quite strong vertical wind shear. Isolated thunderstorms might erupt towards night hours as mid level trough approaches the region, but this in weakening instability will likely further prevent necessary severe threat to issue at least a low end Level 1.

... Eastern Europe ...

Broad region with tstm activity is forecast over Eastern Europe, developing in the moderate instability, which per most of NWP will exceed 1000 J/kg in the zones with the highest threat. Unstable airmass will rapidly spread towards north/northwest as warm front progresses across the region. Mid to upper level flow should be rather weak, generally below 15 m/s, while low level flow is forecast to strenghten, especially in the afternoon/evening hours as the frontal trough spreads towards north, steepening the pressure gradient on the rear side of the surface high pressure system.

The first area with enhanced threat should be the wavy frontal boundary stalling during the day over NW Romania, W Ukraine, E Poland, W Belarus towards the Baltic states. There are some discrepancies between the models regarding the position of the frontal system. Still, easterly to southeasterly surface flow, with upper level flow parallel to the boundary will likely contribute to the quick clustering of DMC into one or more MCS, which might ride along the boundary to the north. Moderate mixing ratios, rather slow cell movement and low LCLs point to the enhanced threat of excessive precipitation.

More isolated development of the DMC is forecas towards the east - south of the warm frontal boundary. Marginally large hail might occur with stronger multicells. Towards the evening hours, with strengthening low level flow, reaching 15-20 m/s at 850 hPa level, LLS values might locally exceed even 15 m/s. With weak wind shear at mid to upper levels of troposphere, it is likely that clustering of cells could result in a squall line progressin towards north. Also, enhanced SREH is simulated with the backing flow, so that brief supercell is not ruled out. Besides marginally large hail, severe wind gusts might occur over the area and towards the evening, as LCLs drop, an isolated tornado is not ruled out either till the boundary layer becomes too stable.