Forecast Update
Valid: Mon 26 May 2008 13:00 to Tue 27 May 2008 06:00 UTC
Issued: Mon 26 May 2008 13:04
Forecaster: GROENEMEIJER

SYNOPSIS

Refer to convective forecast....

DISCUSSION

Belgium, Netherlands, NW Germany, N-central France

The extent of cloudiness associated with a partly stratifrom/partly convective rain zone associated with a diffuse cold front extending in N/S direction across France has been much less than anticpated. Widespread clearings have formed to the north of this area across Belgium, N France and NE France south of a west-east oriented warm front across Belgium.

Visible satellite imagery shows towering cumulus developing across Belgium and the French région Nord. There and later elsewhere, isolated storms are expected to form. Up to 1000 J/kg of CAPE would be available to those storms, that develop in an environment of rather strong deep-layer wind shear of 20-30 m/s and high storm-relative helicity. As a result, they may develop into supercells capable of producing some large hail, and strong winds. Tornadoes are not ruled out either. A preferred location may be the warm front across Belgium that extends into the German Rhineland.

NE, central, E-central France, W Switzerland...

Large breaks have lead to significant clear areas across much of eastern France as well, between several convective clusters. In contrast to the original forecast, it is currently thought that some storms may become surface-based here as well, leading to higher storm intensity and increases the chance of tornadoes. Overall large values of storm-relatively helicity suggest that some supercells may develop here as well. They could produce large hail, damaging winds and perhaps even an isolated tornado.

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