Storm Forecast
Valid: Fri 17 Jun 2011 06:00 to Sat 18 Jun 2011 06:00 UTC
Issued: Thu 16 Jun 2011 20:20
Forecaster: TUSCHY
A level 1 was issued for E-Poland, parts of Belarus, NW-Ukraine, parts of Lithuania and Latvia mainly for severe wind gusts, large hail and isolated tornadoes.
A level 1 was issued for E-France and extreme W-Switzerland mainly for large hail, severe wind gusts and an isolated tornado event. During the night, locally excessive rainfall will be the main hazard.
SYNOPSIS
Progessive pattern persists over Europe as numerous troughs affect central Europe. Weak height gradients are still present over the Mediterranean with mainly diurnal driven thunderstorm activity.
DISCUSSION
...Parts of Sweden ...
Cold upper trough crosses the highlighted region. Steep mid-level lapse rates and some modest LL moisture advection allow roughly 500 J/kg MLCAPE to evolve. Shear remains weak, so an isolated large hail and strong wind gust event will be the main hazard. Thunderstorms gradually decay after sunset, but thunderstorm swath may expand well to the east with isolated activity offshore during the night hours.
... E-Poland, Belarus, W-Ukraine, Lithuania and parts of Latvia ...
Near orthogonal orientation of surface cold front regarding an eastward racing mid-level jet streak allow an organized line of convection to form along the frontal boundary. A warm and moist prefrontal airmass assists in roughly 800 J/kg MLCAPE, so combined with strong forcing, scattered thunderstorms evolve along the cold front, probably lining up into an active squalline. A more widespread wind gust risk is present with a few significant events possible. However, a few large hail and an isolated tornado event can't be ruled out either. The tornado risk may be maximized over E Lithuania and E-Latvia, where directional shear will be maximized. Thunderstorms gradually decay after sunset, however a forced line of showers and isolated thunderstorms may persist well into the night hours.
... S/E France, Switzerland and S-Germany ...
During the afternoon hours, a strongly forced warm front consolidates over the W-Alpine region, lifting rapidly to the north. Latest synop data over SE-France and NW-Italy reveal surface dewpoints in the upper tens, so even bullish GFS calculation does not seem too unrealistic. However, CAPE difference between GFS and EZ remain significant. Also, scattered to widespread initiation is forecast with rapid clustering forecast, so discrete/longer lived thunderstorms are not expected to be too numerous right now. Nevertheless, 0-6 km bulk shear in the order of 20 m/s and similar shear in the lowest 3 km indicate an augmented risk of severe wind gusts and large hail during the initiation stage of any thunderstorm. Also, favorable speed/directional shear within the BL overlaps with modest CAPE, so at least a low end tornado risk will be included into the overall risk scheme. However, rapid clustering is forecast with a transition into a more stratiform rain shield after sunset, as CAPE decays. A 15 m/s LLJ over SE-France advects a very moist airmass into the NE-ward expanding cluster, so heavy rainfall will be an increasing risk, especially over SE-France, SW-Germany and most parts of Switzerland.
... N-France and UK ...
The passage of an intense depression will be monitored closely in next model runs regarding moisture return. Current trends indicate only weak thetae advection with marginal CAPE and positive LIs. However, shear and enhanced LL CAPE may be supportive for rapidly organized showers/isolated thunderstorms with attendant severe risk. In case of better CAPE, an upgrade may be needed.
The rest of the thunderstorm areas will see pulsating storms/multicells with marginal hail and strong wind gusts.
