Storm Forecast
Valid: Mon 21 Dec 2009 06:00 to Tue 22 Dec 2009 06:00 UTC
Issued: Sun 20 Dec 2009 23:58
Forecaster: DAHL

A level 1 was issued across SW Iberia mainly for excessive rainfall.

SYNOPSIS

A deep-layer frontal zone is stretching from the western Atlantic into SW Europe. Cyclogenesis is underway off the Iberian W coast, which will boost the warm advection over SW Europe and the central Mediterranean on Monday. By Tuesday morning, subtropical air will have reached central Europe per latest model guidance. Continental polar/arctic air masses prevail over northern and eastern parts of Europe.

DISCUSSION

... western Iberian peninsula ...

It seems that deep convection will accompany the WAA regime over western Iberia throughout the period. This convection will likely be elevated, with the most notable effect being an augmentation of the precipitation. Especially the low-level shear will be rather strong, suggesting that storm organization, including mesocyclones, may occur. The primary threats with this activity would be severe wind gusts and possibly a tornado or two. However, confidence in SFC-based convection remains rather low at the moment. Highest severe rainfall probabilities will likely exist over SW Iberia.

... eastern Mediterranean ... western Turkey ...

Rather shallow convection may occur in the wake of the cold front extending across western Turkey at the beginning of the period. 0-6 km shear is simulated to exceed 25 m/s, so that some of the cells may briefly develop into linear segments and/or mesocyclones. These may pose some marginal severe wind-gust threat. However, given minimal CAPE, the shallow nature of the storms, as well as their anticipated low coverage, the allover severe risk will be rather small.

... North Sea ... British Isles ...

Comparatively shallow polar-air convection will exist over the North Sea, the eastern Atlantic, and the British Isles. Though most of the clouds will likely not be electrified, the strongest cells may produce a lightning flash or two.