Schweizer Sturmforum

Wednesday 15 August
The picture has not changed much compared to yesterday’s. The cold front should cross the Rhine Valley around 00 UTC. Ahead of this front, some CAPE is expected to develop, albeit not very much owing to weak mid-level lapse rates. However, it should be sufficient to maintain deep convection. Model consensus develops convection around 18 UTC or even a bit later. Current thinking is that thunderstorms will initiate around 18 UTC in the western COPS region and spread eastwards. Shear profiles remain favorable for rapid severe evolution, including a few supercells, main severe threats being damaging wind gusts along with some large hail. Strong low-level shear and ample low-level moisture should support low-level rotation of any supercell that forms, resulting in some threat for a brief tornado or two. However, given somewhat weak CAPE it is currently not expected that storms will grow into large MCSs.
Along the main convergence line associated with the cold-frontal boundary, additional storms should form, which may be organized more linearly, given strong linear low-level forcing. Uncertainty exists about how well the storms will survive along the front through the night. However, the above-mentioned strong largeand mesoscale forcing for upward motion could sustain the convective system through the night. This system would pose mainly a threat for strong/severe wind gusts.