Extended Forecast

Extended Forecast
Valid: Tue 28 Feb 2017 06:00 to Wed 01 Mar 2017 06:00 UTC
Issued: Mon 27 Feb 2017 00:56
Forecaster: VAN DER VELDE

A level 1 was issued for parts of central France, NW Switzerland and S Germany mainly for tornadoes and severe convective wind gusts.


For Tuesday, the large upper trough shifts eastward into central Europe. Models transform a shortwave Atlantic trough swinging around this system into a baroclinic, rapidly developing low with well-defined frontal system, tracking from W France to the region between Luxembourg and Switzerland, onwards to Czech Republic or Austria. The exact position of the occlusion and the amount of CAPE still varies between models and runs, but the scenario of a warm sector with a few hundred J/kg MLCAPE, strong lifting dynamics and a high-end kinematic environment seems quite likely. The 12Z and 18Z Sunday GFS runs placed the area with highest convective threat during the afternoon in the France-Germany border region. There was a solid overlap of CAPE with 1-3 km mean wind speeds over 25-30 m/s with strong potential for severe convective wind gusts, as well as tornadogenesis in the highly sheared conditions (SREH 0-3 km over 350 m2/s2, 0-1 km shear over 17 m/s, 0-6 km shear over 35 m/s). It seems that the low level flow around the west side of the Alps creates a local enhancement of shear and warm air advection into the warm sector. The frontal system is predicted to move very fast. Depending on the amount of expected instability in model runs later on Monday, with less forecast uncertainty the corridor of the warm sector may require a level 2 for the threat of organized convective wind gusts threat and tornadoes.

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