Storm Forecast
Valid: Mon 26 May 2008 06:00 to Tue 27 May 2008 06:00 UTC
Issued: Sun 25 May 2008 18:41
Forecaster: GROENEMEIJER

SYNOPSIS

Embedded within a southerly mid and upper-level flow, an intense jet streak at 300 hPa from eastern Spain to Brittany is slowly moving further northward. In the lower troposphere a 25 m/s low-level jet over eastern France is present on the cold side of a meridionally-oriented baroclinic zone. During the late evening and in the night, a mid-level shortwave trough will move northward out of Algeria.

DISCUSSION

France, NE Spain, western Mediterranean Sea...

During the afternoon hours, an extensive area of precipitation and cloudiness is expected over central and south-central France. To the west and east of this zone, the sun has better chances. On the warm side of the frontal zone, little instability is expected to form during the day as upper-level forcing will be lacking. Scattered storms are however, possible in the cool and moist air-mass over the lower Loire Valley, parts of Brittany and Normandy. Moderate shear and weak CAPE limit the severe threat of storms there. Some small hail will however be possible.

Ahead of the trough approaching northward Algeria, the increasing forcing for upward vertical motion over the western Mediterranean, should lead to widespread initiation of elevated thunderstorms. These will likely reach SErn France and NE Spain after midnight. Simultaneously, a SEly low-level jet into France should strengthen, to over 25 m/s. Substantial amounts of elevated CAPE and the strong low-level winds suggest that a few severe events may occur, for which the level 1 area has been issued. The severe weather would include some large hail and severe wind gusts.

NW Spain, N Portugal...

Scattered storms are expected to develop over the mountains near a mid-level thermal trough. As the air will be cool and moist, small hail and perhaps an isolated funnel cloud or landspout are possible.

Lapland, northern Karelia...

Convection here will develop in an environment with weak shear and CAPE, and will therefore likely not become severe.

E Bulgaria, NW Turkey, E Ukraine...

Ahead of a weak cold front, some storms are expected over these areas. Shear and CAPE should be low enough to minimize the chance of severe weather.

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