Storm Forecast
Valid: Tue 29 Jul 2008 06:00 to Wed 30 Jul 2008 06:00 UTC
Issued: Tue 29 Jul 2008 01:54
Forecaster: VAN DER VELDE

SYNOPSIS

A cold front associated with an Atlantic low pushes farther into Europe, with a band of warm humid BL air at its front side stretching from NE-Spain to the Alps curving to the Benelux and Scotland. Over the continent, MLCAPE values 1000-1500 J/kg are forecast in this zone. Weaker and partially elevated instability occurs near the upper low over the British Isles.

DISCUSSION

...northeastern Spain and southern France...

Deep layer shear is enhanced to over 15 m/s over this region, and SREH 0-3 km up to 250 m2/s2 in combination with about 1000 J/kg CAPE allow strong multicell and supercell thunderstorms with a chance of large hail and severe gusts, especially in the western half of the level 1 region. Downdraft LI and delta-theta-e both of around 15 degrees are supporting the severe gusts threat. Initiation should remain isolated.

...Germany...

WIth ICAPE (column integrated CAPE) values of 2-3 MJ/m2, a strong convergence line and 10 m/s deep layer shear, many storms are expected to cluster in this region and some of those may grow hail of 2-4 cm size, or produce strong to severe gusts due to high LCLs >2000m and downdraft LI>14 degrees at the eastern edge of the high dewpoint band. An MCS may form in the evening, but remains mostly stationary over northern Germany, where increasing low level shear may help sustanance of convection at night. Movement of cells should be slow, perhaps training over the same region for a while, and large amounts of accumulated precipitation in can cause flash flooding in several locations.