Storm Forecast
Valid: Fri 12 Nov 2010 06:00 to Sat 13 Nov 2010 06:00 UTC
Issued: Thu 11 Nov 2010 15:51
Forecaster: TUSCHY
A level 1 was issued for Denmark, the Netherlands, Belgium and parts of Germany mainly for severe wind gusts and an isolated tornado.
A level 1 was issued for Crete and areas to the south mainly for heavy rainfall, marginal hail and strong wind gusts.
SYNOPSIS and DISCUSSION
Gradually filling extratropical cyclone moves from the North Sea to the east. Attendant strong pressure gradient affects areas to its south, namely from France all the way to Belarus. Owing to the more zonal flow, which builds in from the west, geopotential heights over SW Europe increase during the forecast (also ensuring that the pressure gradient remains steep despite the filling cyclone) with tranquil conditions establishing over the Iberian Peninsula. A weakening cut-off over the Ionian Sea causes unsettled conditions with showers and thunderstorms.
No real foci were seen, which could foster organized DMC in a strongly sheared environment. Nevertheless, two areas were highlighted, where BL moisture remains augmented:
...Denmark and extreme N-Germany ...
Some LL moisture from the occlusion, which wrapped around the cyclone's center multiple times, sneaks in from the W/NW beneath cool low/mid-levels. Also, LL CAPE is forecast in this well mixed air mass, so showers/isolated and weakly electrified thunderstorms may pose a severe wind gust and isolated tornado risk, peaking around noon/ during the afternoon hours.
... Central Germany, Belgium and the Netherlands ...
Neither deep convection nor electrified one is forecast. However, with backing winds at LL and the arrival of another wave from France during the day, some LL moisture advection is forecast over the area of interest, resulting in widespread weak to modest LL CAPE release. Keeping in mind that global model resolution may blur areas on the mesoscale, where conditions for somewhat deeper convection change for the better, we don't want to exclude a few better organized showers/a very isolated thunderstorm over the area of interest. Given extreme background shear/helicity (20 m/s LL shear and roughly 500 m^2/s^2 SRH-1) only a temporarily stronger updraft is needed for some storm organization. Severe wind gusts and an isolated tornado risk are therefore added. Already during the afternoon hours, conditions become worse due to vanishing LL CAPE.
... Crete and areas to the south ...
Scattered thunderstorm activity is forecast in the range of the weakening cut-off over the south-central Mediterranean. A few multicells are well possible with locally heavy rainfall, marginal hail and strong wind gusts. Main activity however is forecast south of our forecast area.
