Storm Forecast
Valid: Sat 21 May 2011 06:00 to Sun 22 May 2011 06:00 UTC
Issued: Sat 21 May 2011 05:20
Forecaster: SCHLENCZEK
A level one threat was issued for W-central France mainly for large hail and severe wind gusts.
A level one threat was issued for parts of SE-central Europe mainly for large hail and severe wind gusts.
A level one threat was issued for E Poland, W Belarus and W Ukraine mainly for large hail and severe wind gusts.
SYNOPSIS
An unstable airmass has overspread most portions of Europe. Ahead of a trough which is located west of Ireland, a region with some QG forcing will affect western France during the late afternoon / evening hours. Another upper level disturbance is centered over the western / central Mediterranean. An overlap of significant deep layer shear and moderate instability is missing and therefore no severe weather outbreak is expected. A few regions may profit from some 1000 - 1500 J/kg SBCAPE mostly produced by diurnal heating, and dry mid levels which could lead to some hail and downbursts.
DISCUSSION
...W / C France, N Iberia...
Steep lapse rates and limited moisture in the boundary layer lead to quite high LCL / LFC heights (mostly between 1,5 and 2 km AGL). These conditions may create an environment favourable for isolated severe hail and isolated severe wind gusts. Overall threat requires a marginal level 1 as moderate to high instability is forecast for W France.
...S / central Germany...
The conditions in Germany are comparable to those in France and Iberia, but with less instability. Deep layer shear is in order of 10 m/s and therefore not very favourable for severe weather. Storm motion is expected to be very slow which can lead to a local heavy rain / flash flood event. Large hail and severe wind gusts are not ruled out either but expected rapid clustering of multicells will limit the risk of severe weather. Overall coverage of severe weather should therefore not reach the level 1 criteria.
...Austria, W Hungary, Slovenia, Croatia...
LCL / LFC heights in order of 2 km and locally more than 2 MJ/mē ICAPE are forecast for a broad region of the southeastern parts of central Europe. Even though deep layer shear is in order of only 10 m/s, some organized multicells and pulsating storms should develop. Soundings from Vienna and Zagreb indicate that most of the CAPE should be located at an altitude above the freezing level, which is favourable for isolated large hail. Evaporative cooling may lead to some severe wind gusts as well and overall coverage is expected to meet the level 1 criteria. After sunset, CAPE will decrease and severe events will become less likely.
...SE Poland, Belarus, W Ukraine...
Another local spot of enhanced instability and steep lapse rates is found over the eastern / southeastern parts of Poland, parts of Belarus and the western Ukraine. Some organized multicell storms are expected to be the dominant convective mode and may produce large hail and severe wind gusts.
QPF signals are far below the threshold for an excessive rainfall risk, but the possibility of flash floods will exist in all places where slow moving storms are maintained for a long time.
