Storm Forecast
Valid: Tue 11 Jun 2013 06:00 to Wed 12 Jun 2013 06:00 UTC
Issued: Mon 10 Jun 2013 22:40
Forecaster: TUSCHY

A level 1 was issued for most of SE/E Europe mainly for large hail, strong to severe wind gusts and heavy rainfall amounts.

A level 1 was issued for W-Bulgaria into C-Romania mainly for large hail, strong to severe wind gusts and heavy to isolated excessive rainfall amounts.

The northern tip of the level 1 in W-Russia was issued mainly for an isolated tornado risk.

SYNOPSIS

A complex of two troughs, loosely linked to each other, advances east and results in widespread DMC over SE/E Europe. Strong ridging builds in from the west and suppresses initiation over W-Europe. An unseasonably strong extratropical cyclone takes aim towards Ireland, UK and Scotland, but its influence remains west of our forecast area until Wed., 06Z.

DISCUSSION

...E/SE Europe ...

A wavy frontal boundary, which extends from W-Russia all the way to the Balkan States seems to continue its slow SE-ward shift for the following 24h. However, this boundary won't be the main focus for most vigorous initiation, as a pronounced prefrontal convergence zone is analyzed in surface maps and extends from W-Bulgaria into C-Romania (10th June, 21Z). A combination of surface dewpoints in the low to mid tens along and ahead of that convergence zone beneath modest mid-level lapse rates offers widespread 500-1000 J/kg MLCAPE with decreasing values in the postfrontal air mass to the west (and still ahead of the main frontal boundary). DLS of 10-15 m/s and similar values for the 1-8 km layer point to a risk for well structured multicells with large hail and strong to severe wind gusts. However, any directional shear component remains weak from Moldova to Bulgaria, so rapid clustering is forecast during the evening and overnight hours. Slow storm motions and increasing effective PWs also highlight a constantly increasing flash flood risk, especially for thunderstorms from W-Bulgaria into C-Romania during the overnight hours. A broad level 1 should cover that risk although an isolated extreme event (mainly hail) can't be ruled out. Storms further west (e.g. extreme E-Austria to S-Poland) see less CAPE, but conditions remain prime for slow moving storms which could produce large hail, strong wind gusts and heavy rain.
We added parts of the Balkan States to the level 1 for a similar risk.

Further north, e.g. Ukraine to the north, dynamics become better and we have to deal with a more ponounced frontal boundary, which gradually shifts east/northeast. Placed beneath the right entrance region of a strong mid/upper level jet to the north, scattered to widespread CI along that boundary is likely. Weakening lapse rates become balanced by rich BL moisture (maximized along the boundary itself), so 500-1000 J/kg MLCAPE are forecast with higher values well possible. Best shear and CAPE fields remain displaced through the forecast, but nevertheless, numerous multicells/isolated supercells with large hail and severe wind gusts are likely. The region Moscow-Saint-Petersburg to the east experiences an enhanced tornado risk until noon, as strong LL shear and 500-800 J/kg MLCAPE overlap. Thereafter the risk shifts east of our forecast area.