Storm Forecast
Valid: Mon 15 Dec 2008 06:00 to Tue 16 Dec 2008 06:00 UTC
Issued: Sun 14 Dec 2008 16:50
Forecaster: TUSCHY

SYNOPSIS

Warm air advection downstream of the strong Canadian polar vortex results in rising pressure over NW Europe and an evolving cut-off low over SW-Europe. The cool and stable weather pattern over E-Europe persists for the upcoming forecast period.

DISCUSSION

... Western/central Mediterranean ...

Models agree well in a gradual spin-up of a surface depression over the western Mediterranean during the period. Frigid air upstream of the depression overspreads Spain and areas included over NW Africa. The boundary layer is dry and only sporadic lightning is forecast over the coastal areas of Morocco/NW-Algeria.

Further east, numerous convergence zones and higher mixing ratios ahead of the eastward propagating cold front and beneath cold-mid level airmass support scattered to widespread thunderstorm activity. The highest coverage of storms due to best environmental conditions exist west and north of Corsica, over the E/SE Tyrrhenian Sea, just off the coast of NE-Algeria and later-on also over the N-central Adriatic Sea. A low wet-bulb zero level and some low-end instability release foster the risk of a few marginal hail events. Buoyancy at lowest 3km is on the increase and an isolated waterspout could occur but coverage should be too low for a broad level area.

A small level-1 was issued for a time frame 00Z-06Z as a potent 50m/s mid-level streak approaches from the SW and attendant left exit region overspreads the area with good upper-level divergence. As cold front slides eastwards, scattered thunderstorms are forecast and as directional shear along the front remains strong, an isolated tornado event is possible next to strong wind gusts and marginal hail.