Storm Forecast
Valid: Fri 20 Jul 2012 06:00 to Sat 21 Jul 2012 06:00 UTC
Issued: Thu 19 Jul 2012 23:45
Forecaster: TUSCHY

A level 1 was issued for N-Italy, S-Austria, W-Hungary, far SW-Slovakia and parts of Slovenia mainly for large hail (a very large hail event possible) and strong to severe wind gusts. An isolated tornado event can't be ruled out.

A level 1 was issued for most parts of Austria mainly for heavy rainfall.

A level 1 was issued for parts of SW-Russia mainly for a few tornadoes, large hail and severe wind gust reports.

A level 1 was issued for parts of the C/E-Ukraine mainly for large hail and strong to severe wind gusts.

SYNOPSIS

A large upper trough is still situated over N-Europe. A progressive SW-erly flow regime affects most of Europe with a hot and dry air mass to the south (e.g. Mediterranean).

DISCUSSION

... SW Russia and C/E-Ukraine...

A wave at mid/upper levels, closed below 3km, moves rapidly to the E. At the surface, a progressive warm front moves to the E with a dragging cold front becoming quasi-stationary from SW-Russia into C/E-Ukraine.

Regarding the severe risk, the warm sector will be the area of most concern with strong veering wind profiles (good LL speed and directional shear) next to 30 m/s DLS. Degree of severe coverage however will be dictated by how fast the occlusion process overtakes the warm sector. We expect numerous well organized multicells/supercells with a large hail/severe wind gust and tornado risk. The activity diminishes during the late afternoon hours onwards.

Also, well organized multicells are forecast along the trailing cold front with moderate CAPE/strong shear overlap. Large hail and severe wind gusts will be the main risk, although heavy rain becomes an increasing concern due to storm clustering. Storms gradually weaken during the night hours.

... N-Italy, Slovenia, W-Hungary, far SW-Slovakia and parts of Austria ...

Placed beneath the right entrance of a 30 m/s 500 hPa jet and given moderate capping, we expect scattered thunderstorms to evolve during the early afternoon hours onwards within the highlighted area. Models disagree how far to the south initiation will occur but we see no significant reasons to go too far off the mountains. Given impressive directional and speed shear, a few well organized multicells and supercells are forecast over N-Italy, S-Austria and parts of Slovenia with large hail and severe wind gusts the main risk. An isolated very large hail event can't be ruled out next to an isolated tornado report, given strong LL shear in high resolution model data for S-Austria. The forecast becomes more uncertain over SW-Slovakia and W-Hungary, but models like WRF remain optimistic with initiation in a favorable environment for organized storms. Also, latest synop data reveal good moisture recovery, so the level 1 was expanded far eastwards. A broad upper trough and attendant forcing next to the favorable jet position assist in clustering of storms betimes with heavy rain also for areas to the north (mainly for parts of Austria).

... C/E-Hungary, NW Romania and SW-Ukraine ...

Good model agreement in very isolated initiation along a diffuse/stalling synoptic boundary. Despite good shear, CAPE build-up will be hard to realize, so for now a 15-% lightning area will be added. However, any sporadic storm is capable of producing isolated large hail.
During the evening hours onwards, large-scale forcing increases, but a stable BL/rapidly decaying CAPE and probably induced subsidence from a growing storm cluster over the Alps keep thunderstorm development unlikely during the night.

...Rest of the lightning areas...

Daytime driven thunderstorm activity is forecast beneath a flat upper trough, filled with cold air at mid-levels. A few strong pulsating storms are possible with marginal hail and strong wind gusts. We do not want to rule out a few waterspout reports along the coasts of the Baltic Sea and the coast of Beligum and also an isolated funnel/ tornado report over Belgium (where LL-CAPE is augmented). However the risk remains too marginal for a level area. Thunderstorms decay after sunset.