ESTOFEX: "Conditions become typical for (water)spouts"

Storm Forecast
Valid: Tue 01 Aug 2006 06:00 to Wed 02 Aug 2006 06:00 UTC
Issued: Tue 01 Aug 2006 00:27
Forecaster: VAN DER VELDE

SYNOPSIS

A large depression and upper trough over the North Sea brings an end to hot conditions over France, Benelux, Germany and the British Isles, and with slightly unstable profiles will cause showers and thunderstorms. As cool air pushes into central Europe, scattered thunderstorms are expected to develop along the front in the level 1 area.

DISCUSSION

...Northern Italy to Poland....

With 0-6 km shear reaching >15 m/s and a few hundred to more than 1000 J/kg MLCAPE (GFS... may underestimate for Nrn Italy in this flow), organised multicellular storms and a few supercells are expected to develop, bearing a chance of primarily large hail and severe gusts, the latter especially in the southern part of the area where the environment is drier. The front is forecast to become almost stationary.
Western Hungary has a spot of enhanced SREH and low-level shear in GFS that may also marginally support a tornado besides large hail.

...eastern Spain...

With moderate shear/helicity conditions, but marginal instability (GFS), expect very isolated storms that may become severe with large hail. GFS shows strong convergence signals but does actually not produce convective precipitation.

...UK, Netherlands, Belgium, Germany, Denmark...

Conditions become typical for (water)spouts, especially after today when the flow eases down. Strong low level lapse rates and buoyancy and zones of convergence are likely to produce convection with spout type tornadoes, most of which won't do any damage. Today, the still strong flow could cause an isolated marginally severe gust in the area, and deep layer shear is moderate and could organise a storm well enough to produce very isolated marginally large hail, severe events below level 1 criteria.