Storm Forecast
Valid: Sun 21 Dec 2008 06:00 to Mon 22 Dec 2008 06:00 UTC
Issued: Sat 20 Dec 2008 23:38
Forecaster: SCHLENCZEK

SYNOPSIS

A zonal upper flow pattern has established over the NW Atlantic with an intense cyclone near Iceland. Further upstream, a very cold arctic airmass over eastern Canada is advected southward and rapid cyclogenesis is expected near Newfoundland. Remnants of an occluding surface low move across southern Scandinavia. In the wake of an upper longwave trough over southeastern Europe, thunderstorms should be most likely. A large upper high will persist over western Europe during the period.

DISCUSSION

...W Scandinavia...

Ahead of the upper trough, a strong southwesterly flow will establish over southern Norway at lower levels while the left exit of a 80 m/s jet streak approaches. Very strong QG forcing will be in place in a region with low-end instability and about 30 m/s wind speeds at 850 hPa. Although deep layer shear is only in order of 25 m/s at most places, shallow convective lines may develop and pose a threat of severe convectively-enhanced gusts. Lightning activity will be rather sporadic but a LVL1 should be warranted.

...E Mediterranean, Aegean Sea...

In the wake of the trough, a few hundred J/kg of CAPE will be in place in a region with weak forcing and 15 m/s deep layer shear. Most of the thunderstorms should not produce severe weather but isolated marginally severe hail / strong gusts are not ruled out.