Mesoscale Discussion
Valid: Mon 28 Jun 2021 14:00 to Mon 28 Jun 2021 18:00 UTC
Issued: Mon 28 Jun 2021 14:31
Forecaster: TUSCHY

MESOSCALE DISCUSSION:

Environmental conditions are prime for organized convection with 12Z soundings/AMDARs over Switzerland/SW Germany revealing improved veering of the mid-level flow. Sampled H800-600 hPa EML broadens the mid-level CAPE profile with strong SR flow for deviating storms.

Already ongoing supercell over the Jura Mountains seems to be a long-lived feature as it enters an increasingly unstable air mass to its E/NE. Merging with cells to its south is expected and a gradually maturing conglomerate of supercells/bow structures should affect N Switzerland during the following hours before entering NE-Switzerland/far SW Germany as a well developed/severe bow echo.
DLS in the 20-25 m/s range with 15 m/s 0-3km shear and widening hodographs with a deepening well mixed BL indicate a risk of all hazards including very large hail, damaging wind gusts and excessive rain (especially during cell merging).
Of conern is the partially extreme looping of the hodograph with LCLs around 800 m over N-Switzerland into far S Germany during the evening. Even with some potential model issues (blow up of DMC), similar (although weaker) signals are present in coarser models like the IFS. Hence N-Switzerland into far SW Germany should be monitored for an augmented tornado threat during the following hours beside the regionally very severe gust threat.

Further north (Black Forest, Swabian Alb), shear at all levels weakens somewhat but still supports multicells/a few supercells during CI. All hazards are possible including large hail, excessive rain and severe downbursts.
During the evening hours, mid-level flow contiues to weaken in response to the splitting jet configuration, so with dominant 0-3 km inflow into these thunderstorms, training is possible with extreme rainfall amounts and flash flooding.
The tornado risk is a bit lower with less 0-1/3 km shear, but LCLs of 500-800 m and good streamwise vorticity inflow for deviating storms keeps this threat alive until the evening/early night hours.
Rapidly intensifying upper divergence beneath splitting upper jets, deep low-/mid tropospheric moisture convergence and increasing QG forcing should induce an upscale growth into a large cluster of storms which shifts N/NE during the night. Excessive rain becomes the main hazard beside local hail/severe wind gusts.

Note: The duration of this MD does not reflect the duration of the severe event, which continues well into the night. This MD is just a nowcast update.