Storm Forecast
Valid: Fri 19 Dec 2008 06:00 to Sat 20 Dec 2008 06:00 UTC
Issued: Thu 18 Dec 2008 17:41
Forecaster: TUSCHY

SYNOPSIS

Quiescent weather conditions go on for the majority of Europe with two intense high pressure areas, one over SW Europe and the other one over NE/E-Europe. In-between both, a flat upper trough remains more or less stationary for the forecast period and attendant colder mid tropospheric air supports some thunder over parts of the central/eastern Mediterranean and the western Black Sea.
An intense surface depression evolves westnorthwest of Ireland and emerges into the N-North Sea during the night hours.

DISCUSSION

... Scotland and highlighted areas ...

Modest humid air feeds into the rapidly developing depression WNW of Ireland during the morning hours, but a gradual weakening trend of the theta-e tongue is forecast as system occludes just north of Sotland. So the main missing ingredient is instability with only traces forecast by GFS. However, an intense coupling in vorticity advection maps is present, crossing Scotland during the afternoon and evening hours just as the occlusion/cold front passes by. Mid-levels over Scotland have a hard time to cool down, so even elevated instability is questionable although not impossible, refered to the past few model runs. We think that the best environment for enhanced convection along the passing front exist over N-Scotland and north of that area. This part of the front remains the focus as it passes the N-North Sea.
Shear along this front is in the extreme range with winds at 850hPa in excess of 40-45m/s, not weaker at mid-levels, so widespread gusts above hurricane force are likely even without enhanced deep convection. We decided not to issue any level/highlighted areas as attendance of convection looks quite limited, but this area has to be monitored.

As the depression occludes, the lower troposphere becomes more humid while upper-levels remain cold, so the depression's core should be quite active regarding convection. Confidence in widespread lightning activity is too low to go with a broad thunderstorm area and hence we stuck with the climatology. To the south of the depression's center, the environment is conducive for widespread damaging wind gusts over the N-North Sea during the night hours, as 45m/s at 850hPa in a cool/moist and mixed airmass spread eastwards.