Storm Forecast
Valid: Sun 26 Apr 2009 06:00 to Mon 27 Apr 2009 06:00 UTC
Issued: Sun 26 Apr 2009 03:26
Forecaster: VAN DER VELDE

SYNOPSIS

A large upper trough with its axis over Spain, France and UK shifts eastward. Scattered patches of marginal CAPE are distributed over/around Spain, S and W France, NW Italy, and Netherlands/NW Germany.
Given the low amount of instability, thunderstorm areas are drawn where most-unstable EL heights appear sufficiently cold (-20°), and where LFC-LCL differences are small and convergence near the surface relatively strong.

DISCUSSION

...southern France, northern Italy...

The most active weather feature is the cold front slowly dragging over the Provence region and northwestern Italy, with moist air being lifted upslope, producing tens of mm of rain, sometimes from convection. Where capping is low and convergence strong, isolated storms may develop, most likely close to the coastlines with some backbuilding. While low level and deep layer vertical wind shear are moderate and slightly in support of a tornado chance, the degree of instability appears too limited, hence no level 1.

...southern Spain, Balearic islands...

Another active region is southern Spain, where the narrow tip of the upper trough creates strong lift by DCVA in slightly unstable airmass. This is predicted by the models to activate over the western Mediterranean during the night with a chance of thunder in the Balearic region.