Storm Forecast
Valid: Sat 13 Apr 2013 06:00 to Sun 14 Apr 2013 06:00 UTC
Issued: Sat 13 Apr 2013 02:30
Forecaster: PISTOTNIK

A level 1 was issued for parts of Serbia and Bulgaria for large hail.

SYNOPSIS

A zonal flow has temporally established over Europe. Increasing warm air advection results in upper-level ridging across the Western half of the continent and the build-up of a surface high pressure system centered over the Alpine region towards the end of the forecast period.
Further downstream, a weak upper-level trough and its attendant cold front slowly shift from Central to Eastern Europe.

DISCUSSION

... the Balkans, Romania, Moldova, Ukraine ...

The cold front is forecast to align to the Carpathian mountain chain in Romania early in the forecast period, while diurnal heating will drive the temperatures to the lower 20ies and the dewpoints to the lower 10s further to the South and East, resulting in CAPE around 500 J/kg. Frontal convergence and diurnal valley wind systems will allow for convective initiation, supported by the passage of a moderate vorticity lobe aloft. Isolated to scattered thunderstorms are forecast to form near to the cold front in the noon to afternoon hours. Highest coverage and possible clustering of storms is expected over Eastern Romania and Moldova, where cold pool formation may lead to some stronger wind gusts as well. However, the weak vertical wind shear makes severe weather too unlikely to issue any level area.
Further Southwest, coverage of thunderstorms will be lower due to the reduced activity of the cold front and its more trailing alignment, but deep layer shear is increased to values between 15 and 20 m/s beneath a disintegrating jet streak. A few storms may organize into multicells over the Balkans, and a marginal level 1 was drawn for a hail risk where CAPE and shear overlap seems to be best over parts of Serbia and Bulgaria.
Storms will become elevated and dissipate rather soon in the evening hours over the Ukraine and the Black Sea.

... Poland and around ...

Postfrontal showers and weakly electrified storms are expected in the afternoon. Limited CAPE and weak vertical wind shear should preclude any severe weather threat.