Storm Forecast
Valid: Fri 22 Dec 2006 06:00 to Sat 23 Dec 2006 06:00 UTC
Issued: Thu 21 Dec 2006 17:01
Forecaster: TUSCHY

SYNOPSIS

An intense high pressure area over United Kingdom will slowly shift towards the ESE / SE during the next 24 hours.
A strongly positive tilted longwave trough over the Mediterranean will continue to retrograde and will start to transform into a separated upper-level low over far SW Europe.
An outbreak of very cold air ( mainly at mid-levels ) will affect parts of N-Sweden, Finland and extreme NW Russia.

DISCUSSION

.... The western and central Mediterranean ...

One area with enhanced thunderstorm potential can be found mainly north and west of the Balearic Islands . A pool of cold mid-level air ( 500hPa < -30°C and 700hPa ~ -15°C ) will reach the region during the early morning hours from the NE and will continue to shift towards the west.
Given SSTs of 15-16°C and this thermodynamic environment, conditions will become fine for instability release and modified sounding of Mallorca indicates the possibility of up to 500 J/kg SBCAPE just NW and W of the Balearic Islands. The main inhibiting factor looks like to be a pretty dry boundary layer airmass due to offshore winds from France.
Did not include a fetch area south of France due to the favorable environment and a slowly veering LL wind field during the latter part of the forecast period which should support another round of enhanced thunderstorm potential around the Balearic Islands.
Scattered thunderstorms can be expected but DLS will be marginal high enough for a low-end severe wind gust threat.
There is also a marginal risk of waterspouts especially during the daytime hours around and NW of the Balearic Islands due to steep LL and mid-level lapse rates but aforementioned dry boundary layer will keep LCLs pretty high during this time frame.

Otherwise an area from the Strait of Gibraltar to Sardinia and Sicily will have conditions, which are favorable for scattered TSTM development. Shear should be too weak for storms to organize.

Another area of enhanced TSTM development can be expected east of Sicily but models indicate that best shear and thermodynamic environment will be separated. Hence, no higher probabilities were issued.

...Parts of N-Norway, Sweden, Finland and extreme NW Russia...

An outbreak of extremely cold air from Greenland occured yesterday and this airmass will reach the area of interest during the early morning hours. The boundary layer airmass will be already be modified due to the passage over the open water but mid-level air will be very cold ( 500 hPa < -40°C ). This airmass will overspread the aforementioned areas from the WNW and should support an environment with very steep mid-level lapse rates. A region was highlighted, where topography and track of coldest airmass should support isolated thunderstorm development.
A broad sector with enhanced 0-1km SRH and low LCLs will be present and an isolated tornado / severe wind gust threat can't be ruled out but storm coverage will be too low for warranting a level - 1.