Storm Forecast
Valid: Sat 24 Jul 2010 06:00 to Sun 25 Jul 2010 06:00 UTC
Issued: Sat 24 Jul 2010 05:17
Forecaster: VAN DER VELDE

A level 2 (and 1) was issued for the Balkan and eastern Italy mainly for severe convective wind gusts and large hail.
A level 1 was issued for the Baltic Sea area mainly for excessive (convective) rain and a chance of large hail and tornadoes.
A level 1 was issued for eastern Spain mainly for large hail.

SYNOPSIS

A large mid-level trough has taken position over central Europe. Western Europe is now in a cooler weather pattern with northwestern winds, while warm moist air is found over the Balkan, Poland and Baltic states. The main surface low moves slowly northward over Poland. From this low, a cold front bends southeastward to Romania and back to the west, while a warm front stretches across the Baltic states and southern Finland, slowly advancing northwestward. Balkan, Italy, Spain and British Isles are locations with an unstable aimass where a mid-level shortwave trough passes which will likely help to activate convection.

DISCUSSION

...N Poland, Baltic Sea, W Lithuania, Latvia, Estonia...

Along the warm front significant SREH (200-300 m²/s²) is present as a result of veering winds with height due to warm air advection. There is a small overlap region with MLCAPE (which is not so high, around 500 J/kg) and moderate deep-layer shear, 15-20 m/s. Supercells are therefore likely near and north of the surface front. Also 0-1 km shear is elevated: values over 10 m/s, which could help tornadogenesis. Across the front LCL height decreases from 2000 m in the east to around 1000 m in the west. Large hail, isolated severe wind gusts and an isolated tornado are possible. A negative factor is that 1-8 km shear >20 m/s is not overlapping with CAPE.
Over NW Poland and the Baltic Sea near Sweden, the stalling front will cause excessive rain, due also to large precipitable water combined with high saturation (PW-SatDef > 40 mm), part of which can fall from convective storms.

...Balkan and Italy...

A band of deep layer shear around 20-30 m/s ahead of a strong mid-level PV anomaly runs over a region with about 1000 J/kg MLCAPE. This is most the case in the west, where however MLCAPE is lower. SREH around 100 m²/s², locally more, is also present. Storms can develop into multicell clusters/lines and supercells, producing large hail and severe wind gusts which can be widespread, which is helped by large delta-theta-e values (>20K). On the other hand, the gusts and hail threat could be limited by low LCL height seen in GFS model, but this is likely because of already initiated convection.

...eastern Spain...

A relatively small area with unstable air, high LCLs, >20 m/s DLS, delta-theta-e > 20K and somewhat enhanced SREH can produce one or two supercells with a chance of large hail and severe wind gusts.

...Denmark...

Modest potential is present for an isolated (water)spout.