Storm Forecast
Valid: Wed 23 May 2012 06:00 to Thu 24 May 2012 06:00 UTC
Issued: Wed 23 May 2012 06:32
Forecaster: PUCIK

A level 1 was issued for BENELUX, Western Germany and Eastern France mainly for marginally large hail, brief downburst and to the lesser degree for excessive precipitation.

A level 1 was issued for Northern Italy mainly for marginally large hail or brief downbursts.

SYNOPSIS

A blocking pattern is currently in progression over Europe, with a significant amplifying ridge stretching from Iberia towards Northern Scandinavia and a weakening mid-level low over Southeastern Europe. Closer to the surface, a large high presssure system builds over Northern Europe, while a widespread, but shallow low dominates southeastern part of the continent. Between these two features, a relatively warm airmass in the weak easterly flow is observed over most of Central and Western Europe. As cooler mid-level temperatures spread towards southwest thanks tot he mid-level ridge, high lapse rates result in a widespread built up of a latent instability during the day. Mostly disorganised convection, forming in the environment of weak to moderate instability and weak vertical wind shear can be expected in the large extents of Europe.

DISCUSSION

... Western Germany, Eastern France, BENELUX ...

Models are in relatively good agreement on the moderate latent instability release during the day, with MLCAPE values likely in the range of 1000-2000 J/kg. This is supported by the 00 UTC sounding measurements from the region, which already show 500-1000 J/kg of MUCAPE. Convection will likely be driven diurnally, thanks to the local initiating factors without any significant synoptic scale support. Only a slight advection of higher PV values is simulated by GFS towards the afternoon. In the environment of a weak wind shear, mostly disorganised convection is anticipated. Nevertheless, especially if CAPE values will approach 2000 J/kg, strong pulse updrafts might produce marginally large hail and brief downbursts. Due to the slow movement of DMC, locally excessive precipitation is not ruled out either.

... Northern Italy ...

Moderate CAPE along with slightly enhanced wind shear in this region might pose a risk of a few strong multicells developing especially by evening hours with a threat of marginally large hail or a brief downburst. Activity will likely depend on the local lifting factors, e.g. orography and will be strongly diurnally driven, with rapid cessation of severe threat after the sunset.