Storm Forecast Valid: Mon 11 Aug 2014 06:00 to Tue 12 Aug 2014 06:00 UTC Issued: Mon 11 Aug 2014 07:58 Forecaster: GROENEMEIJER
A level 1 was issued for SW Finland, the Baltic States, eastern Poland, western Belarus, extreme western Ukraine, Slovakia, eastern Czech Republic, much of Austria, Slovenia, north Croatia, much of Hungary, northern Italy and southern Switzerland.
South of a mid-/upper-level low over the northern North Sea, a very strong (25-35 m/s @ 500 hPa) almost zonal jet is present. A cold front that initially stretches from the Baltic Sea across western Poland to the Alps and northern Spain.
Level 1 area ...
Ahead of the front, a zone of very humid air has formed with dew point temperatures of almost 20 C or even slightly above observed at 0600 UTC. The soundings throughout the area show rather poor low to mid-level lapse rates so that only weak to moderate instability (1000 J/kg MLCAPE) will probably form during the course of the day.
It appears likely that a number of well-organized multicells will form, and some supercells not ruled out as interact with 15 m/s deep-layer shear. These storms should be able to produce some (2 - 5 cm) hail, localized severe winds and very heavy rainfall.
Across northern Italy, deep-layer shear should be stronger (20-25 m/s), but the coverage of storms, so that we refrain from issuing a level 2 for that area.
North Sea Coasts, southern Scandinavia...
Widespread convection will occur across the southern North Sea and southern Scandinavia. The rather strong low-level wind field will limit the risk of waterspouts, but quite intense storms should be able to form. Some mostly small hail may occur.