Storm Forecast
Valid: Sun 31 Mar 2013 06:00 to Mon 01 Apr 2013 06:00 UTC
Issued: Sun 31 Mar 2013 07:32
Forecaster: VAN DER VELDE

A level 1 was issued for parts of Hungary, Romania, Serbia mainly for a chance of large hail, tornadoes and severe convective gusts.

A level 1 was issued for the southwestern Balkan mainly for large hail.

A level 1 was issued for Portugal and western Spain mainly for chance of tornadoes.

SYNOPSIS

South of the cold northern half of Europe, a negatively tilted upper trough shifts into southeastern Europe. A jet of 30-45 m/s at 300 hPa produces kinematically favorable conditions for organized convection in the warm sector, with marked temperature contrasts around Hungary, strong low level convergence and upper PV advection over the cold front.
Another low pressure system with a moist, unstable warm sector and strong vertical shear lies over the western Iberian Peninsula.

DISCUSSION

...Hungary, northern Balkan...

The degree of forcing and vertical shear are strongly supportive of severe weather. To which extent depends on how much CAPE can be released. GFS model counting on 7 g/kg mixing ratio produces <500 J/kg MLCAPE and such is also the impression from 00Z soundings. Given the extensive cloudiness, warming might be more problematic than the model suggests. On the other hand the Zagreb sounding is so moist that elevated convection can occur above the boundary layer. The convective mode should be mainly linear, given the concentrated lifting, but some supercells with large hail are likely included. Forecast hodographs are pretty straight with 0-6 km shear around 25 m/s. 0-1 km shear can reach 15 m/s which supports tornadoes. An severe wind gust is possible and should be the main mode in case of a linear system, but buoyancy is a limiting factor.

...southern Balkan...

In this area the low level shear is less strong. SREH is higher for left-moving storms than for right-moving. Convective mode favors more isolated and clustered cells over linear, and supercells can develop. Large hail is the main severe weather threat. There is some chance of elevated storms which could persist into the night, moving towards Bulgaria.

...Portugal...

Very similar shear conditions to those in the northern Balkan, but the CAPE is predicted to be weaker and forcing as well. Even 35 m/s deep layer shear is sketched here. 10-15 m/s 0-1 km shear and very low LCL heights support tornadoes, most chance would be roughly in the northern half of Portugal.