Storm Forecast
Valid: Sun 19 Jun 2011 06:00 to Mon 20 Jun 2011 06:00 UTC
Issued: Sat 18 Jun 2011 17:13
Forecaster: TUSCHY
A level 2 was issued for parts of Romania, Ukraine and Belarus mainly for more widespread severe wind gusts, a few significant/damaging events possible.
A level 1 surrounds the level 2 and was issued mainly for severe wind gusts, large hail and a few tornado events.
A level 1 was issued for parts of Poland, the Czech Republic and parts of Austria mainly for a few large hail reports.
SYNOPSIS
A large-scale cold-core vortex is situated over N-Europe and steers numerous short waves over most parts of west/central and east Europe towards the east. More quiescent conditions exist over the Mediterranean, as geopotential heights slowly increase.
DISCUSSION
... Most parts of Romania, W-Moldova, W-Ukraine, E-Belarus and parts of SW-Russia ...
A sharp short wave rounds the base of the large-scale cyclonic vortex and remains a progressive feature during the forecast, travelling from Austria all the way to Belarus. At the surface, an eastward sliding cold front will be the spot for scattered thunderstorms beneath the aforementioned northeastward racing sharp vorticity lobe. So regarding initiation, no doubts exists that active cold front passage will occur in the highlighted areas.
Overall, latest synop data ahead of the front reveal a well mixed and dry 1-2 km layer above the surface with surface dewpoints in the mid tens. However, a swath with better moisture evolves along the eastward moving cold front, where convergent flow, strong moisture influx and high PWAT indicate a favorable set-up for deep convection. Modest mid-level lapse rates overspread this corridor, so 500 - 1000 J/kg MLCAPE are a reasonable forecast.
Storm mode is a bit more tricky to forecast. There exists no doubts regarding well organized multicells and embedded supercells, as 0-6 km bulk shear increases to 20 m/s with similar values in the lowest 3 km. However, front is aligned near parallel to the background flow over far NW-Romania and W-Ukraine. That's not the best environment for long-lived discrete supercells. Current thinking is that during initiation phase, all kind of severe modi can be expected, including large hail, severe wind gusts and an isolated tornado event. However, given concentrated shear within lowest 3 km and deep mixed prefrontal air mass, rapid upscale growth into numerous bow echoes with severe to damaging straightline wind events is forecast. Those features probably ride towards the northeast along the eastward moving cold front, mainly affecting far NW-Romania and W-Ukraine. After sunset, thunderstorms gradually weaken betimes with a transition into a more stratiform rain cluster with isolated embedded thunderstorms over central Ukraine, E-Moldova and E-Romania.
Over E-Belarus and areas further to the east, DLS will be somewhat weaker (15-20 m/s) with better directional shear available. So a similar mutlicell/supercell risk is expected, however with an augmented chance for a few longer lived/discrete events over E-Belarus. Large hail, severe wind gusts and an isolated tornado event are expected within this environment. During the evening and night hours, thunderstorm clusters from the activity further to the south probably affect the area with the main risk then being strong wind gusts and excessive rainfall.
... Rest of the lightning areas ...
Weak shear/modest instability preclude organized thunderstorm activity for the rest of the lightning areas.
Nevertheless, a few strong thunderstorms over SW-Poland, the E-Czech Republic and N/NE-Austria may contain large hail due to a low WBZ and hence a marginal level 1 for hail was introduced.
