Schweizer Sturmforum

nordspot hat geschrieben:Jemand im Forum wollte den heutigen Tag in die Tonne treten wg Hochdruck über Süddeutschland und Nordschweiz

DISCUSSION

...Southeastern France, Northwestern Italy through Switzerland, Southeastern Germany, Czech Republic and Poland/Western Ukraine...

A complicated forecast for this region does not allow to pinpoint very precisely the locations with the greatest threats. Nevertheless, slightly to moderately unstable airmass (MLCAPE values around 1000 J/kg) will likely be in place, as agreed by most of NWP and soundings from the previous forecast period. Weak to moderate vertical wind shear with bulk values of 10-15 m/s in the 0-6 km layer might be enhanced by the backing flow nearby the surface low centers, yielding over 15 m/s of DLS and enhanced SREH. Stronger mid-level flow might also be observed in the vicinity of the subtle short-wave trough towards the evening hours.

Location of the low centers and of the boundary will likely play the most important role in the evolution of the tomorrow´s scenario, along with the timing of the short-wave trough. As of 5 UTC, there is already a large multicell cluster along the warm front. Initiation of DMC today will be tied to the:

A/ frontal boundaries - e.g. lifting warm front over Poland or close to the wavy cold front over Switzerland and Germany

B/ orography - Alpine range and northern part of Carpathians.

C/ short-wave trough in the late afternoon and evening hours.

Widespread coverage of thunderstorms is most likely around and to the north of the Alpine Range especially when the forward flank of the short-wave approaches and also along the advancing warm front over Poland. Another MCS is very likely by the evening hours and a bulls-eye in QPF is discernible in several NWP consecutive runs over Bavaria. Moderate instability and shear might at first result in a well organised, strong multicells with isolated large hail or marginally severe wind gusts. Brief supercells are not ruled out especially in the spots with backed surface flow. Towards the late afternoon or evening, clustering will yield one or more MCS travelling towards NE along wavy cold front, with the most significant threat of excessive precipitation, especially along or on the cool side of the boundary, where very moist airmass and low LCLs might foster high precip. efficiency in DMC. Excessive precipitation might also very well occur with the morning MCS lifting along the warm front over Poland. Severe wind gusts might occur in MCS in the late afternoon, in case that it is rooted in the boundary layer, but the threat will likely not be very high.