Storm Forecast

Storm Forecast
Valid: Sat 10 Dec 2011 06:00 to Sun 11 Dec 2011 06:00 UTC
Issued: Fri 09 Dec 2011 17:45
Forecaster: TUSCHY

SYNOPSIS and DISCUSSION

A short break is in store with no serious wind event forecast during the upcoming 24 hours. Briskly westerlies still affect the North Sea, Baltic Sea and adjacent areas with 20 m/s and more at 850 hPa. Frigid -40 C and less at 500 hPa cross those areas and allow somewhat deeper updrafts to develop. I only excluded parts of the SW-Baltic Sea, where SSTs remain significantly lower compared to the rest. As flat ridging works in from the west, thunderstorm chances decrease from west to east during the forecast period. Nevertheless, any shower/thunderstorm will still be able to mix down stronger winds from above, so a strong to severe wind gust risk is forecast. With EL temperatures quite warm, only sporadic electrified activity is expected and no level was added for that event. Even a low prob. thunderstorm area seems very optimistic, but I can't exclude a few short lived thunderstorm events mainly offshore.

A weakening upper low enters the far W-Mediterranean and assists in gradually lowering geopotential heights. Model signals regarding thunderstorm initiation are mixed (optimistic/pessimistic), so the focus was set to the area with best BL moisture and coldest mid-levels. Also an isolated event is possible along westward facing coasts due to some moisture flux convergence (e.g. E-coast of the Adriatic Sea). One comment about an isolated spout risk along the coast of the E-Adriatic Sea: LL CAPE is augmented and high resolution model data reveals some signals for a developing convergence zone parallel to the coast. If a stronger updraft evolves atop/rides along that convergence zone, an isolated waterspout can't be excluded. Otherwise, no severe is expected and overall activity will be sporadic.

Marginal hail may accompany stronger showers/sporadic thunderstorms along the coast of W-Portugal and NW-Spain. Activity diminishes from north to south and ends after sunset.

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