Storm Forecast
Valid: Thu 18 Jun 2009 06:00 to Fri 19 Jun 2009 06:00 UTC
Issued: Wed 17 Jun 2009 22:12
Forecaster: GATZEN

SYNOPSIS

To the south of an intense trough over eastern Europe and another polar trough over the north-western European portions, a mid-level westerly jet is present from the Channel to the Ukraine. While the north-western trough starts to amplify over western Europe, the jet moves northward over central and eastern Europe. At lower levels, cool air masses have spread across eastern Europe in the range of the trough axis. Polar air masses do also enter north-western Europe. Ahead of the cold front, a rather weak thermal wave moves across central Europe and leads to some warm air advection. A tongue of moist low-level air mass advects into France and southern Germany in the evening hours, while rather dry air masses are present over eastern and northern Europe. Rich low-level moisture is present from the Iberian Peninsula to the Mediterranean and the southern Balkans.

DISCUSSION

Iberian Peninsula, southern France, southern Italy, and southern Balkans

Rich low-level moisture and moderately steep lapse rates are expected on Thursday, and diurnal heating will likely create CAPE in the order of 1000 J/kg. Forcing is weak and initiation is expected along of outflow-boundaries, sea-breeze fronts, and mountains. While vertical wind shear is rather weak, single cells seem to be the main convective mode. Chance for organized convection is highest over southern France and from southern Italy to the southern Balkans, where vertical wind shear will be slightly higher.

Given rich moisture and slow-moving storms, local flash flooding may occur. Additionally, stronger storms may produce large hail. Storms are expected to weaken after sunset.

Central France to Alps

A tongue of moist air mass spreads eastward into the Alps ahead of the cold front, and rather steep lapse rates are forecast to be sufficient for some elevated CAPE during the night hours. As the mid-level jet spreads southward, vertical wind shear increases, but current thinking is that instability will be weak and storms will not manage to become well-organized. However, storms that root to the moist boundary-layer may encounter moderately strong low-level vertical wind shear, and a tornado cannot be ruled out completely.