Storm Forecast
Valid: Sun 11 Oct 2009 06:00 to Mon 12 Oct 2009 06:00 UTC
Issued: Sat 10 Oct 2009 21:56
Forecaster: SCHLENCZEK
A level 1 was issued for the southern Netherlands and NW Germany mainly for tornadoes.
A level 1 was issued for parts of the Adriatic Sea and the Balkans mainly for excessive precipitation and large hail and to a lesser extent for tornadoes.
A level 1 was issued for W Romania and SW / W Ukraine mainly for large hail and tornadoes.
SYNOPSIS
The upper trough over Germany has moved eastward into the Czech Republic and will lead to unstable conditions in parts of Czech / Slovak Rep., S Poland and W Ukraine. Cyclogenesis is expected over Poland, leading to a 1000 hPa surface low which moves ESE-ward. In the afternoon, another upper shortwave trough over the North Sea is forecast to cross the Benelux countries and NW Germany.
Another upper trough with convective activity over the Ionian Sea moves eastward, affecting the S Balkans and the E Mediterranean. The persistent upper high over SW Iberia leads to stable conditions in SW Europe.
DISCUSSION
...Netherlands, N Belgium, NW Germany...
With the approaching upper trough, a region of very strong DCVA affects the SW North Sea and the Netherlands in the early afternoon. In the southern part of the Netherlands and NW Germany, deep layer shear will increase to values between 15 and 30 m/s in an environment with some hundred J/kg CAPE. SRH3 should reach values between 150 and 250 mē/sē which favors rotating updrafts. Rich BL moisture leads to a low cloud base and, combined with about 100 J/kg MLCAPE in the lowest 3 km and 10 - 15 m/s low level shear, to a chance of tornadoes. The tornado threat should be greatest in the late afternoon, decreasing in the night hours when shear and instability decrease.
...Adriatic Sea, Balkans...
Although deep layer shear has decreased to values around 10 m/s, this region should have the greatest chance of severe storms on Sunday. About 1500 J/kg MLCAPE are forecast which will lead to multicells with isolated large hail and heavy rainfall. Over the Adriatic Sea, more than 200 J/kg CAPE will be available in the lowest 3 km and an isolated waterspout may occur. Later in the period, the intense convective precipitation area will extend to the northeast.
...W Romania, W Ukraine...
Ahead of the developing low pressure system, moderately warm and moist air is advected into the western and central parts of Romania and Ukraine. QG forcing should be sufficient for convective initiation and some multicells will develop in an environment with a few hundred J/kg CAPE and 20 m/s deep layer shear. The main convective mode should be well-organized multicells and low-topped supercells as SRH in order of 300 mē/sē is forecast. Some storms may be accompanied by marginally severe hail and especially in the W Ukraine, LLS in order of 10 - 15 m/s will increase the chance of an isolated tornado. Convective activity depends on diurnal heating and therefore the threat of severe weather will diminish after sunset.
