Storm Forecast
Valid: Fri 15 Dec 2006 06:00 to Sat 16 Dec 2006 06:00 UTC
Issued: Thu 14 Dec 2006 21:33
Forecaster: GATZEN

SYNOPSIS

A sharp ridge axis connects eastern Atlantic ridge with a high over central Europe and Balkans. At its northern flank, a very strong jet streak travels eastward over southern Scandinavia during the forecast period. To the south, a cut-off low over northern Algeria remains. Instable air masses north of the jet streak as well as in the range of the cut off will lead to some convection on Friday.

DISCUSSION

Western Mediterranean

Situation over western Mediterranean is comparable to Thursday: An easterly surface flow advects rather moist low-level maritime air mass in a region with rather steep lapse rates in the range of the upper trough. Latest models indicate that instability will spread to the north and west as low-level dry continental air mass from Algeria advects northward. Given weak CIN, showers and thunderstorms will likely go on further north during the period. Organized thunderstorms seem to be not very likely as deep layer vertical wind shear will only be around 10 m/s. However, a southerly jet curving around the cut off is expected alond the Tunisian coast late in the period, and deep layer wind shear will increase. A few organized thunderstorms are forecast to develop, but chance for severe weather is expected to be weak, though. Strong wind gusts and small hail are forecast. Best potential for some tornadoes exists near the coasts of Tunisia and Corsica, where low-level vertical wind shear is expected to reach more than 10 m/s in the range of south-easterly low-level jet. Current decision is not to issue a level 1 due to rather weak deep layer wind shear and weakeining thermodynamic profiles compared to Thursday.

South-western Norway

While strong upper jet crosses the Norwegian coast, huge vertical wind shear is forecast. Relatively moist and unstable air mass is lifted at the western side of the Scandinavian mountains. Thunderstorms are forecast again, and given strong low-level vertical wind shear and also high 0-1 km SRH values, high winds and a few tornadoes are expected to occur. Further west, low-level helicity is forecast to be weaker, and chance for embedded mesocyclones is weaker. Convection is also expected to weaken in the wake of the jet streak, and high winds are expected to be related to strong synoptic winds mostly.