Storm Forecast
Valid: Wed 03 Oct 2007 06:00 to Thu 04 Oct 2007 06:00 UTC
Issued: Tue 02 Oct 2007 21:09
Forecaster: GATZEN

SYNOPSIS

The polar jet stream splits W of Europe. The southern branch forms an omega over central Mediterranean with two flanking cut-off lows over Iberian Peninsula and southern Turkey. The subtropic high over Tunisia ridges into Alpine region and western Scandinavia. Small cut-off lows over the British Isles and the Baltic States are also flanking the Scandinavia ridge. A vort-max/jet streak now over Iberian Peninsula is expected to travel eastward across France/central Germany during the period. At low levels ... WAA will remain from western Mediterranean to France, Benelux, Alps, and south-western Germany. Boundary-layer moisture has started to increase especially over the Mediterranean Sea as well as from northern France to Benelux, and south-western Germany.

DISCUSSION

Eastern Spain and Balearic Islands, southern France

An EML originating from the Atlas spreads northward over west Mediterranean. The boundary-layer is quite strongly capped although there is rich low-level moisture. Latest models indicate that the capping inversion will temporarily weaken near the Spanish coasts, due to a few jet streaks providing QG forcing and mid-level cooling. CAPE up to 1000 J/kg is expected. Thunderstorms are forecast to go on throughout the period, moving northward and gradually weakening over France. With strong vertical wind shear about 25 m/s DLS and favorable veering profiles indicated by 200 J/kg 0-3 km SRH, thunderstorms will likely organize. Best chances for a back-building MCSs exist over eastern Spain in the range of a jet streak and low-level convergence, while more isolated convection including supercells are more likely to the east. Locally large hail and severe wind gusts ate forecast. Best chances for tornadoes exist at the eastern flank of the MCS over eastern Spain due to expected strong southerly low-level winds. Even a strong tornado is not ruled out. Convection is forecast to weaken in the evening/night hours.

Northern France into Benelux, and Germany

Latest Trappes sounding indicates a moist and nearly uncapped boundary-layer that is expected over northern France, Benelux, and south-western Germany during the period. This moist boundary-layer has developed in the range of a frontal boundary that forms a wave moving eastward. Low-level convergence as well as some daytime heating will help for destabilization and initiation in the afternoon/evening hours over northern France, Benelux, and southwestern Germany. In the range of a short-wave trough/jet streak, moderate vertical wind shear is forecast, and strong thunderstorms may develop, with slight chance for severe hail and wind gusts. Tornadoes are not completely ruled out given locally strong low-level buoyancy. Convection will likely go on during the night as QG forcing and low-level convergence will remain.

Baltic States

In the range of the cut-off low, rich low-level moisture and weak vertical wind shear are present, and a few waterspouts may develop along the coasts.