Storm Forecast
Valid: Sun 30 May 2010 06:00 to Mon 31 May 2010 06:00 UTC
Issued: Sun 30 May 2010 05:40
Forecaster: SCHLENCZEK
A level 1 was issued for Benelux, W Germany and E France mainly for severe wind gusts and an isolated tornado.
A level 1 was issued for N Italy and Slovenia mainly for severe wind gusts, large hail and an isolated tornado.
A level 1 was issued for S Lithuania, E Slovak Rep. and E Poland mainly for large hail and severe wind gusts.
A level 1 was issued for NW Russia mainly for severe wind gusts.
SYNOPSIS
Between an upper ridge over the east-central Atlantic and an upper low over Scotland, an intense northwesterly upper jet streak translates from the Irish Sea towards NW Italy. Ahead of the upper trough, a thermal wave is present over the southern North Sea and cyclogenesis is expected. Downstream of this low pressure system, moderately warm air is advected into parts of E / SE Europe. Another upper low is present over Finland, moving to the east.
DISCUSSION
...S Netherlands, Belgium, Luxembourg, extreme W / SW Germany, extreme E France...
Some low-end instability will form near the centre of the upper low over the SW North Sea during the afternoon. This plume of unstable air will travel to the southeast with the left exit of a 45 m/s jet streak at 500 hPa, affecting most parts of the Benelux countries, W Germany and E France. Locally, 0-6 km deep layer shear reaches values around 40 - 45 m/s and EL temperatures are forecast around -30°C so that storms may profit from the intense vertical shear. Current thinking is that some convective lines will develop, posing a threat of severe wind gusts. It is likely that some storms within the line will contain mesocyclones. LLS will reach values of 10 - 13 m/s and in this environment with rich BL moisture, an isolated tornado may form. The severe wind gust / tornado threat should be maximised between 15 UTC and 00 UTC.
...N Italy, N Adriatic, Slovenia...
The southern tip of the jet streak will reach Italy during the late afternoon when diurnal heating and WAA at lower levels should have produced some hundred J/kg CAPE. Deep layer shear is forecast to intensify during the evening hours, reaching 30 - 40 m/s in NE Italy and Slovenia. In this environment, well-organised multicellular lines and low-topped supercells may form, capable of producing isolated marginally severe hail, severe wind gusts and an isolated tornado. Thunderstorm activity should gradually decrease around midnight.
...Slovak Rep., E Poland, S Lithuania...
A small southerly jet streak is present over this region during the afternoon hours, leading to locally 15 - 20 m/s deep layer shear in an environment with approx. 1 kJ/kg MLCAPE. Some well-organised multicells and a few supercells may form in this environment, posing a threat of large hail and severe wind gusts. In the night hours, a region with subsidence will overspread the region and convective activity should decrease.
...most parts of SE Europe, Black Sea region, W Russia...
There are several regions in SE and E Europe where CAPE is locally enhanced but deep layer shear is forecast to be less than 10 m/s. Some single-cell storms and briefly organised multicells may produce an isolated large hail event. Given the isolated nature of such an event, no threat level was issued.
...NW Russia...
Near the southern tip of an upper trough over Finland, deep layer shear will increase to 20 - 25 m/s over NW Russia in an environment with some low-end instability. Mid level winds should reach values around 15 m/s which may allow an isolated severe wind gust in this region.
