Storm Forecast
Valid: Thu 02 Aug 2007 06:00 to Fri 03 Aug 2007 06:00 UTC
Issued: Wed 01 Aug 2007 21:13
Forecaster: GATZEN

SYNOPSIS

Strong upper trough has moved into the North Sea. Its axis will propagate eastward over France reaching Germany in the night hours. Ahead of the trough axis, quite intense short-wave trough now over France will rapidly move across Germany and southern Baltic Sea during the period. A narrow tongue of warm air mass will spread into southeast Germany/eastern Alps ahead of this feature. Cold air mass spreads into northwest Europe in the range of the trough. The surface cold front is expected to reach the south coast of France, where convective activity is likely.

DISCUSSION

Southeastern Germany, northern Austria, Czech Rep

Strong WAA is expected during the period, and an elevated mixed layer will likely be in place during the day. Southerly winds and Föhn will likely inhibit convective activity initially, and temp will likely reach 29..33°C during the day. With easterly winds north of the Alps, low-level air mass will be dry, although weak moisture increase can be expected underneath the inversion. Current thinking is that surface-based instability will be relatively weak and strongly capped. However, models do show strong QG forcing at the anticyclonic entrance of a jet streak over Germany as well as in the range of the eastward moving trough axis. Thunderstorms will likely develop during the afternoon/evening hours. Given dry low levels, strong cold pools may be possible, and due to strong vertical wind shear, a convective line with embedded bows may be possible. Most significant severe threat will be severe wind gusts. Isolated large hail is not excluded with the stronger cells. Thunderstorms are forecast to move across Austria and Czech Rep. during the evening hours. An upgrade may be warranted when low-level moisture will significantly increase north of the Alps that make surface-based convection more likely.

Southern France, northern Italy, western Alps

Along the cold front, moist and warm air mass is expected to remain from eastern Spain to southern France, and northern Italy. Diurnal heating will likely be sufficient for initiation in the range of outflow-boundaries and upslope flow regimes. Thunderstorms are forecast. Given moderate vertical wind shear in the range of strong mid-level jet streak, thunderstorms may be well-organized, and supercells are not ruled out. Limiting factor will be rather dry air mass. Additionally, best lapse rates are forecast to be replaced by colder air mass. Nevertheless, strong QG forcing in the range of propagating trough axis will likely be sufficient for strong thunderstorms that may merge into an MCS over western Alpine region, where intense precipitation is possible. Isolated large hail is also forecast with the stronger storms.