Schweizer Sturmforum

Southern France, northern Italy, Alpine region, and Germany

Rich boundary-layer moisture has developed over north-east Mediterranean as indicated by latest Barcelona sounding and surface observations over southern France. Although wind will be from the west in the morning hours, strong moisture return is expected on WED in the range of a developing southerly low-level jet ahead of extending short-wave trough over Spain and approaching cold front over central/western France. In the range of the frontal boundary and over northern Italy, rather cool mid-level air mass will likely allow for instability. To the south, warm air mass above the boundary-layer will be a limiting factor for sufficient instability. Current thinking is that convection will develop in the morning hours in the range of the first DCVA maximum spreading from southern France to northern Italy. Later in the period, instability is expected to increase south of the frontal boundary, and given strong quasi-geostrophic forcing ahead of another approaching jet streak over Spain, convection will also initiate from central France to western Alps, spreading eastwards during the evening hours. With strong vertical wind shear due to southerly low-level winds and strong mid-level jet (up to 25 m/s 0-6 km and 15 m/s 0-3 km vertical wind shear) multicell clusters and embedded mesocyclones are forecast. Large hail may occur initially with more isolated mesocyclones, while severe wind gusts are forecast with bowing segments in the range of multicell clusters. Given strong low-level vertical wind shear in the range of the low-level jet, tornadoes are also forecast near the frontal boundary over France and western Alps. Although low-level vertical wind shear decreases to the east isolated tornadoes are not ruled out over Germany along the frontal boundary. Convection will likely merge into a more elevated MCS over Germany given strong QG forcing. Potential for severe storms is greatest over France, where an upgrade to level 2 may be warranted when low-level instability will be strong, indicated that strong tornadoes may become more likely.

Starkniederschläge vom 16. bis 18. September 2006

Feuchtwarme Mittelmeerluft sorgte für ergiebige Regenfälle

Original von Stefan Wichtrach
Letzte Nacht zog hier eine Windfront mit starken Böen durch (stärker als an der SMA in Bern). Ein starker Temperaturanstieg war damit verbunden. Heute Morgen war wieder alles normal. Was war das?