Storm Forecast
Valid: Sat 12 Jan 2013 06:00 to Sun 13 Jan 2013 06:00 UTC
Issued: Fri 11 Jan 2013 15:31
Forecaster: PISTOTNIK

No threat levels were issued.

SYNOPSIS

Most of the European continent is under cyclonic influence, with a central cold-core low situated over Poland and satellites over the North Sea and the Bay of Biscay. All of them are gradually filling up. Polar air has invaded most of Northern, Central and Eastern Europe.
Along the Southern flank of the extensive low pressure system, a more or less zonal jet stream runs across the Mediterranean region. An embedded short-wave trough clears the Aegean Sea towards Turkey in the first half of the day. A second, more powerful short-wave trough enters Portugal and Spain from the Atlantic Ocean during daytime. Due to the limited instability (CAPE does not exceed 100 to 200 J/kg) and the lack of pronounced frontal structures, mostly isolated and non-severe thunderstorm activity is expected.

DISCUSSION

... Greece, Turkey ...

A diffuse surface low gradually moves East ahead of the mentioned short-wave trough at upper levels. Showers and isolated thunderstorms will affect the Ionean and Aegean Sea in the first half of the day. One or two stronger storms with a chance of marginally severe wind gusts are not ruled out over the Aegean Sea, which is crossed by a belt of ehanced deep-layer shear up to 20 m/s before noon.
Later in the day, synoptic-scale subsidence in the wake of the trough and a shift to Northerly (offshore) surface winds will start to suppress further thunderstorms. Isolated and non-severe activity is still possible in the area of Crete and Rhodes in the afternoon and off the Turkish South coast in the evening and overnight.

... Portugal, Spain, France (mainly coastal areas) ...

Isolated to scattered thundery showers can occur throughout the forecast period over the Bay of Biscay and adjacent coastlines in the range of the old cyclone with cold mid-levels and weak vertical wind shear.
Further South, an impressive vorticity lobe ahead of an upper-level trough and in the left exit of an associated jet streak starts to spread over Portugal and Spain. Deep-layer shear is boosted to values around 40 m/s, but CAPE is forecast to be scarce and probably also limited to lower levels the further South it gets, making an overlap of instability and shear questionable. Nonetheless, the strong lift support can be sufficient to create showers and isolated thunderstorms in the second half of the day, which might bring marginally severe wind gusts. Activity gradually decays while moving inland.
Towards early Sunday morning, the vorticity lobe will also approach the Ligurian Sea. Mid-level cooling and a lee cyclogensis offshore of Catalonia could allow the formation of first thunderstorms between the Balearic Islands and Corsica.