Storm Forecast
Valid: Sat 31 Mar 2012 06:00 to Sun 01 Apr 2012 06:00 UTC
Issued: Sat 31 Mar 2012 05:50
Forecaster: VAN DER VELDE
A level 1 was issued for eastern Poland mainly for a chance of severe wind gusts or tornado.
A level 1 was issued for NW Algeria mainly for large hail.
SYNOPSIS
Low pressure systems are present over southwestern Iberian Peninsula and over Lithuania/Belarus. The latter sets up a strong wind field and upper jet at its south side, partially overlapping the slightly unstable air. Very spotty SBCAPE appears in Italy and the Balkan.
DISCUSSION
...Poland and surrounding regions...
Only very slight CAPE due to lacking moisture appears in GFS and HiRLAM models over central Poland and farther north. A very well defined potential vorticity maximum / dynamic tropopause lowering digs into the cold front/occlusion in eastern Poland, providing necessary lift. This will likely cause a strongly forced linear convective system to form with locally some thunder and isolated severe wind gust chance due to flow stronger than 20 m/s in the lowest kilometers. 0-6 km shear is stronger than 30 m/s due to the jet. 0-1 km shear is mostly located south of the cold front, where ELs are also lower, and reaches 10-15 m/s, sufficient for tornadoes. However, confidence in severe weather is low, given poor instability and orientation angle of cold front to the shear vector (too parallel).
...NW Algeria...
20 m/s deep layer shear overlaps a region with decent instability and steep lapse rates. Some supercells with large hail may occur.
...Iberian peninsula...
A low shear environment in the higher MLCAPE region will limit severe potential of the thunderstorms, which likely will be quite numerous. Some shear (even 15 m/s) is present slightly northeast of it, at the flank of the upper low, but instability is weak there.
...northern Croatia and surroundings...
This area develops CAPE in GFS but not most other models. Hence confidence is low in convective development, but if it does, wind shear values are strong and threat should be redetermined.
