Storm Forecast
Valid: Sat 22 Dec 2007 06:00 to Sun 23 Dec 2007 06:00 UTC
Issued: Fri 21 Dec 2007 19:18
Forecaster: TUSCHY

SYNOPSIS

Finally, pressure gradients over Europe start to flatten but for this forecast period, no significant changes are expected.
A broad and gradually weakening upper-level low over the Iberian Peninsula responds to a strong jet on its downstream side. This streak helps to lift the trough constantly towards the NE, before becoming stationary over NE Spain / SW France as geopotential height gradients and therefore the strength of the jet weaken.
This has no effect on the ridge over SE Europe as no WAA can be established to supports this feature and the gradual weakening trend will continue.
A distinctive upper-level trough just north of Scotland will race eastwards while very cold air overspreads parts of NW Russia.

DISCUSSION

... Scotland ...

A sharp thermal trough crosses the area from the west between 12Z and 18Z. Cool down will be temporarily as warm front from another depression approaches from the west. Time - frame for enhanced thunderstorm potential will be a nearly 3h period ( between 12Z and 15Z ) just behind the cold front, as mixing ratio indicates still moderate values and a significant cool down at all levels starts. Shear at lower levels is enhanced, especially along the coastal areas of N-Scotland, but forecast hodographs are quite unidirectional with a strong NW-erly component. Hence, strong wind gusts and marginal hail can be expected but nothing severe.

... Strait of Gibraltar and the western Mediterranean...

Weak shear and low-end instability preclude an organized thunderstorm risk and no severe thunderstorms are forecast.