Storm Forecast
Valid: Fri 08 Apr 2011 06:00 to Sat 09 Apr 2011 06:00 UTC
Issued: Thu 07 Apr 2011 15:23
Forecaster: TUSCHY

A level 1 was issued for parts of Sweden mainly for severe wind gusts and an isolated tornado.

SYNOPSIS and DISCUSSION

Blocking high pattern persists over Europe.

Focus for enhanced convection remains the strong frontal zone over east-central Europe. Shear beneath 50 m/s mid-level jet is very strong, but limited CAPE precludes a more widespread risk for organized convection. Two time frames exist, where at least an isolated severe event is possible:

N-Romania, Moldova and parts of the Ukraine, 6-12 Z:

A thermal trough crosses those areas during that time frame from the NW, increasing mid-level lapse rates within a diffluent streamline pattern. Limited CAPE and shear preclude organized storms, despite a few marginal hail events.

Parts of Sweden, 12-18 Z:

During the morning hours, a strong depression moves ashore along the N-central coast of Norway with an extensive warm sector covering most parts of Norway and Sweden. A combination of diabatic heating, somewhat enhanced BL moisture and steepening lapse rates allow modest SBCAPE to evolve...up to 400 J/kg. Shear at all levels supports organized convection with severe wind gusts being the main risk. The tornado risk may be limited due to an augmented LCL but an isolated event can't be ruled out. Main concern is a limited thunderstorm coverage due to persistent subsidence in the lee of the mountains, but models agree in a strong PVA/NVA couplet to cross the highlighted areas, so at least isolated thunderstorms are forecast.

SE Poland to Romania after 21 Z:

Another mid/upper level impulse with a loosely organized surface cold front moves to the south/southeast. Somewhat better prefrontal moisture is present, but placement beneath pronounced deep-layer baroclinic zone precludes more robust CAPE profiles. Instead, shallow convection is expected, supported by enhanced LL CAPE forecasts. Main concern is the 25-35 m/s 0-3 km shear or winds up to 30 m/s at 850 hPa. Any line-up along the cold front with somewhat better organized updraft/downdraft features may assist in downward transport of those wind speeds. Right now, limited confidence in the development of any thunderstorm precludes a risk area. However this region will be monitored for better prefrontal moisture recovery and therefore and augmentend severe to damaging wind gust risk.