Storm Forecast
Valid: Fri 27 Apr 2007 06:00 to Sat 28 Apr 2007 06:00 UTC
Issued: Thu 26 Apr 2007 19:36
Forecaster: TUSCHY

SYNOPSIS

Weak pressure differences prevail over Europe with high pressure still strengthening over north-central Europe. In-between this feature and an ill-defined upper-level depression over SW Europe, a warm and humid airmass will be present supporting widespread shower / thunderstorm activity.
The western and central Mediterranean will see diurnal driven, weak thunderstorms, while eastern Europe should stay dry .

A cold front over Sweden and Finland procures the influx of a pretty cold airmass, which slides slowly towards the east.

DISCUSSION

...France, SW - UK...

No big changes compared to yesterday.
Strengthening high pressure configuration ( upper-level center somewhere over N-Germany with attendant low-level center just NNE of Scotland ) and a weak upper-level low over SW Europe will continue to feed a warm and humid airmass over France towards the NW.
Yesterday's synop reports indicated a pronounced moisture boundary over north - central France, which should be again the main focus for thunderstorm development during the next 24 hours.
Expect widespread 100-300 J/kg instability release with isolated higher amounts in areas where boundary layer dewpoints will top 15°C.

DLS of 10-15m/s will be present over extreme eastern France / western Switzerland and western / northwestern France. Isolated stronger pulsating cells would pose a hail threat although hail size should stay subsevere.
Another limiting factor for large hail will be constantly weakening lapse rates.

The same for SW-UK, where mostly subsevere hail can be expected with stronger cells.

...Spain and parts of Portugal...

A slowly eastward shifting upper-level low will continue to affect Spain and parts of Portugal.
Mainly diurnal driven thunderstorm activity will affect N / NE and E Spain, where somewhat steeper lapse rates and locally enhanced SRH values indicate an isolated large hail threat.
Risk should be too isolated for issuing higher probabilities.

... Finland - Estonia eastwards...

The focus for an isolated and short-lived thunderstorm will be along an eastward moving cold front. There are no indications that the environment will support more than a localized thunderstorm risk and hence no area will be highlighted.