Storm Forecast
Valid: Sat 11 Nov 2006 06:00 to Sun 12 Nov 2006 06:00 UTC
Issued: Fri 10 Nov 2006 20:27
Forecaster: TUSCHY

SYNOPSIS

A strong NW flow will set up over Ireland and United Kingdom and should mark the start of a slow ESE progression of an intense upper-level trough.
An already weakening upper-level trough over the SE Mediterranean will continue its eastward progression, while most of SW Europe will be influenced by a strong high pressure area.
Very cold conditions prevail for most parts of W / NW Russia.

DISCUSSION

...The North Sea and parts of the Norwegian Sea...

Main forecast challenge will be to pinpoint areas of enhanced TSTM activity in a broad region of slightly unstable atmosphere.
Latest IR images (10th November,18Z) show a large area of enhanced convective activity southeast of Iceland, situated under the coldest mid-level airmass and SW of Iceland, where latest IR-loops indicate a developing cyclonic low-level rotation.
This system, also caught by GFS, showing an area of enhanced mid-level PVA, will enter the highlighted area during the early morning hours from the west.
Current thinking is that a small-scale polar vortex will enter the North Sea during the early morning hours, but conditions during the 06-12Z time frame look not conducive for any significant development of this vortex , due to warming at mid-levels and pretty diffuse upper-level forcing, when steering upper-level low starts a weakening trend.
Anyway, GFS indicates a broad area of low-end instability release west of Norway and Denmark and will highlight an area, where possible track of this vortex and instability will overlap and also the coastal areas of SW Norway, where topographic induced lift could support a short-lived thunderstorm.

...N-Germany,Denmark and the Netherlands...

A southward moving cold front will cross the Netherlands and N-Germany during the morning hours, but weak forcing and only slow cooling at mid-levels should suppress any thunderstorms threat.
A more interesting time frame will be 18Z onwards, when a tongue of moiste air ,combined with a significant cool down of the mid-levels should support vigorous convective activity over the SE North Sea .
Models indicate only low-end instability release, but favorable kinematic parameters for an enhaned severe wind gust and small hail threat with any stronger shower / thunderstorm, which can manage to develop.
Forecast soundings show some veering and low LCLs and an isolated tornado can't be ruled out.
An update may become necessary, when new model runs confirm this possibility.

The same for Denmark and the western Baltic Sea, where enhanced convective activity under the pool of cold mid-level air can be expected.
Shear will abate further towards the east and so does the storm organisation risk.

...SE Mediterranean Sea...

Widely scattered TSTM activity can be expected with an slowly SE-ward shifting upper-level trough, but the area of most significant thunderstorm development should stay well separated from the best kinematic environment , so don't expect any significant storm organisation.
Main threat will be a risk for intense rain, when storms start to develop into a cluster.
During the early evening hours, the thunderstorms should slowly move out to the east and hence out of the area of responsibility.

...Central Italy...

A SE-ward shifting upper-level disturbance could locally support enough lift for an isolated TSTM development over Corsica, the central Tyrrhenian Sea and central Italy, but coverage should stay too low for highlighting any specific area.