Storm Forecast
Valid: Sun 12 Aug 2012 06:00 to Mon 13 Aug 2012 06:00 UTC
Issued: Sun 12 Aug 2012 08:38
Forecaster: VAN DER VELDE

A level 1 was issued for Slovakia, S Poland, N Hungary, N and E Romania mainly for isolated excessive convective precipitation.

A level 1 was issued for southeast Balkan and northern Turkey mainly for excessive convective precipitation and large hail.

A level 1 was issued for eastern Ukraine mainly for large hail.

A level 1 was issued for NE Spain, SE France, N Italy mainly for large hail and isolated excessive convective precipitation.


SYNOPSIS

A blocking high pressure area lies over Scandinavia. There is an Atlantic low with a trough and warm airmass over the British Isles, while a large upper low is found over eastern Europe, centered over the Ukraine-Romania border. Its influence reaches from eastern Czech Republic to Turkey and eastern Ukraine. Meanwhile, the Saharan/Spanish plume of high lapse rates shifts from Spain towards Italy, creating capped CAPE in most areas, with some signs of cap weakening along western Italy later at night.

DISCUSSION

...Slovakia, S Poland, N Hungary, N and E Romania...

A slight threat of isolated excessive convective rainfall events exists due to slow storm motion vectors, persistence of a PV feature and low level upslope flow. LCLs are below 800m. CAPE is only slight and may limit the threat.

...S Bulgaria, E Greece, N Turkey...

Northwestern Turkey is in a northerly flow of moist unstable airmass (1000-1500 J/kg MLCAPE) and will encounter lifting over mountains. LCL heights are low and predicted storm motion vectors also are only a few meters per second, strongly enhancing excessive rain potential. Additionally, around 15 m/s 0-6 km shear is forecast and increases the potential for supercells, in particular in mountainous terrain with chances of large hail. Large delta-theta-e around 20 degrees enhances wet microburst chance (isolated severe wind gusts). Higher LCL heights to the south (central Turkey) are more favorable for gusts and hail. Forcing may be a bit weak with a PV tongue just touching northern Turkey.

...Ukraine...

15 m/s shear allows multicells and supercells with large hail, profiting from 1000-2000 J/ kg MLCAPE. Storms are likely to and probably severe wind gusts and develop first over SE Ukraine and then move as MCS northwestward during the night. Dynamic forcing is lacking although a distinct warm front marks the western extent of the unstable airmass.

...NE Spain, SE France, N Italy...

10-20 m/s deep layer shear is present in these areas and storms will be triggered over the more complex terrain. It is not unlikely that a few brief supercells develop and produce large hail or excessive precipitation (the latter mainly around the FR-IT border where LCL low / PW high and storm motion slow).