Storm Forecast
Valid: Sun 11 Jan 2015 06:00 to Mon 12 Jan 2015 06:00 UTC
Issued: Sat 10 Jan 2015 22:53
Forecaster: PISTOTNIK

A level 1 was issued for Denmark, parts of Germany and Poland, and the Russian exclave of Kaliningrad for severe convective wind gusts.

SYNOPSIS

After bringing a serious winter storm across northwestern and central Europe, cyclone "Felix" slowly moves from Estonia into adjacent Russia while it starts to fill up. It leaves a still very strong westerly to northwesterly flow across the continent.
An embedded upper-level trough amplifies into central Europe and the Balkans. The British Isles experience a temporary relief from stormy conditions under a weak upper-level ridge.
The Iberian Peninsula and much of France can enjoy calm and mild weather under a subtropical high pressure area.

DISCUSSION

... Adriatic Sea into SE Europe ...

The cold front of cyclone "Felix" enters the Adriatic Sea and the Balkans. It is slowed down by weak wave developments in Romania and in northern Italy and loses its formerly sharp structure over this complex terrain.
Limited area models forecast a temporary re-organization of the cold front into a narrow convective rainband only over two areas: (1) in the afternoon to evening over Croatia, Bosnia-Hercegovina and Montenegro, and (2) towards the end of the forecast period over northwestern Turkey. Isolated severe wind gusts are not ruled out, and the snow level will quickly drop to low levels during the brief intense showers. It is unlikely that these convective lines will grow deep enough to produce thunder, though.
Slightly ahead of the cold front, low-end CAPE will build over the Adriatic Sea in the afternoon, as strong lift and cooling upper-levels spread southeastward ahead of the trough axis. Isolated storms are possible. The complicated wind field may provide pockets of enhanced vertical wind shear, but the lack of CAPE will likely preclude any better storm organization. A brief period of severe Bora winds will follow the cold front passage along the eastern Adriatic coast, but should be detached from the thunderstorm activity and is hence not included into our threat level scheme.

... N-central Europe ...

Behind the storm cyclone, a broad stream of maritime polar air is advected across the North Sea into Denmark, Germany, Poland, Kaliningrad and the Baltic states. Surface friction over land enhances vertical wind shear (10-15 m/s) and storm-relative helicity (100-200 m^2/s^2) mainly in the lowest kilometer, while the deep vertical mixing allows very little vertical wind shear further up. The main trough axis leaves Germany by 15 UTC, but various small-scale vorticity maxima continue to overspread the regions further east with prolonged periods of lift until late in the forecast period. Due to uncertainties of their placement and timing, a broad level 1 and low probability thunder area are issued.
Vivid shower activity may grow deep enough to produce a few lightning strikes. Background winds between 25 and 30 m/s at 850 hPa are sufficient to bring isolated to scattered severe wind gusts down to the surface. Most of the convection will be disorganized, but if discrete updrafts can benefit from locally enhanced low-level shear and helicity, brief rotation and a short-lived tornado are not ruled out.
Convection will spread east- and southward while it slowly decays in the evening and overnight.

In vicinity to the cyclone's center, widespread severe to extreme wind gusts (25-40 m/s) will likely still affect coastal areas of Lithuania, Latvia, Kaliningrad and NE Poland in the beginning of the forecast period. As electrified convection is very unlikely, these areas are not upgraded to a higher risk level. The wind field will relax after 12 UTC. Otherwise, the same as written above applies to these areas.

... British Isles ...

The frontal system of the next powerful cyclone will enter the British Isles in the second half of the forecast period. Another major winter storm is expected! However, no deep convection will be involed till the end of the current forecast period yet.