Storm Forecast
Valid: Mon 15 May 2006 06:00 to Tue 16 May 2006 06:00 UTC
Issued: Sun 14 May 2006 21:14
Forecaster: GROENEMEIJER

SYNOPSIS

A prolonged severe weather episode mainly affecting western Europe appears to be in store for the upcoming days.

The easterly progression of a broad area of southwesterly flow downstream of a trough over the Atlantic should create strong wind shear.

Southerly low-level flow ahead of several disturbances should bring high-theta-e air northward in several impulses over western continental Europe over the next few days.
The first impulse is expected during this forecast period.

DISCUSSION

NE France, NW Switzerland, extreme SE Benelux, and extreme SW Germany...

Low-level southerly flow over France is expected to increase during the day bringing a tongue of warm, moist air northeastward into the level 1 area. GFS is probably on the aggresive side advertising 0-1 km average mixing ratios to increase more than 2 g/kg within the moist tongue. Nevertheless, enough moistening should occur to allow for he development of MLCAPE in the range of 500-1000 J/kg.

Scattered storms are expected to develop over northern, central and perhaps southwestern France starting in the mid-to late afternoon. As deep-layer shear is expected to increase during that time ...15-20 m/s 0-6 km bulk shear is forecast... storms should be able to organise into well-organised multicells and perhaps a couple of supercells. These should be capable of producing large hail and strong to marginally severe gusts. As storms gradually cluster, some linear organisation is likely and wind threat will likely develop.

As the convection becomes elevated in nature during the evening hours, they willlikely move eastward overnight into southern and central Germany while the severe threat diminishes.

Spain, Portugal

Rather strong 15-20 m/s 0-6 km bulk shear is expected to develop over much of the peninsula during the day. Strong capping of marginal instability is expected to prevent widespread thunderstorm development for much of the day. A few isolated storms over Galicia and the Pyrenees appear to be possible. These may develop brief low-end severe weather, but given the only few 100's of J/kg CAPE available, the threat should be rather low.

During the late evening an impulse of QG forcing for upward motion is forecast to overspread the peninsula leading to destabilisation and possibly widespread initiation of elevated storms. Although the shear in the storm-bearing layer should only be about 15 m/s, a few rotating storms cannot be ruled out....and a small risk of large hail will be present. The overall threat of severe weather appears to be slightly too low to warrant a threat level 1.