Storm Forecast
Valid: Sun 18 Jan 2009 06:00 to Mon 19 Jan 2009 06:00 UTC
Issued: Sat 17 Jan 2009 22:14
Forecaster: SCHLENCZEK

SYNOPSIS

A strong zonal upper flow pattern has established over the North Atlantic with an impressive 100 m/s westerly jet streak southwest of the British Isles. In the vicinity of the jet's left exit region over the North Sea, an intense 940hPa surface low will shift northeastward while occluding. The next intense cyclone will develop further upstream on sunday afternoon / evening. Its cold front will cross western UK and northwestern France during the night hours and rather shallow but organized convection may develop along the cold front.

High over low blocking will persist for some more days over Russia and an upper level cut-off low over the N Maghreb States moves southward during the period. Over the Mediterranean area, stable conditions will continue.

DISCUSSION

...Ireland, W UK, NW France...

On Sunday morning, showers and thunderstorms are expected in the unstable post-frontal airmass over the British Isles where low-level winds in order of 20 - 25 m/s will be in place. Weak directional shear should minimize the tornado threat but isolated severe gusts may occur. In the afternoon, the approaching warm front of the next cyclone and upper WAA will lead to stable conditions. This will change again around 00 UTC on Monday when the upper vort-max of the next shortwave trough arrives. In an environment with marginal CAPE but very strong (35 m/s) LL shear and locally more than 600 J/kg SRH1 / 1000 J/kg SRH3, shallow convective lines may develop, capable of producing severe convectively-enhanced gusts, in some places even more than 32 m/s, and maybe a few tornadoes. Uncertainties with respect to instability and forcing exist and an update may follow in the evening.

...Other regions...

Showers and thunderstorms with sporadic lightning and gusty winds may also develop over the North Sea, N France, Belgium, the Netherlands and NW Germany. Another area with possible thunderstorms is southern Norway.