Storm Forecast
Valid: Mon 01 Oct 2007 06:00 to Tue 02 Oct 2007 06:00 UTC
Issued: Sun 30 Sep 2007 20:54
Forecaster: GROENEMEIJER

SYNOPSIS

Monday morning at 06:00 UTC... a broad mid-tropospheric ridge is located over the western Mediterranean while a closed vertically-stacked low about 500 km west of Cape Finesterre is almost stationary. Between these two systems slight warm air advection takes place ahead of a frontal zone stretching form southern Protugal to the Bay of Biscay.

Over northern Europe, a trough over central Sweden progresses slowly eastward reaching western Finland on Tuesday morning. This system is filled with slightly unstable cold air, allowing for scattered thunderstorms to occur.

A band of moisture belonging to an old frontal system stretches from Finland southward over the Baltic States along the Polish eastern border to western Romania. There, some storms are expected to form as well as across parts of Greece.

DISCUSSION

Spain, Portugal, south France, central France...

A weak shortwave trough, initially located over the NW Iberian peninsula should move northeastward reaching northern France by midnight. In the early morning, a number of storms are likely already ongoing over western and central Spain and Portugal along the aforementioned frontal zone.
During the late afternoon and into evening, storms are expected to develop across north-central Spain and gradually into France as well.
Relatively strong, 20-25 m/s, deep-layer shear indicates that some risk of storm organization into multicells, small lines and perhaps a short-lived supercell should be possible, despite the low values of CAPE around 500 J/kg expected. Hence, it is possible that strong wind gusts, and possible hail exceed the severe limits locally and a threat level 1 has been issued.