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Low stratus top

Foehn chart

In the cold season, between the beginning of October and the 10th of March, fog or low stratus often occur in the Midland (Swiss Plateau) due to the shorter and weaker radation period. The upper limit of low stratus depends on the pressure gradient towards the north of Switzerland.

The study of Courvoisier shows the relationship between the pressure difference Payerne/CH-Strasbourg/F and the upper limit of low stratus. The forecast is based on the statistical method MOS developed by Meteomedia with hourly updates.

The relationship shows an uncertainty of +/- 100m and works best for longer lasting low stratus periods due to persistent high pressure. The relationship does not work for residual humidity or for the cases without any low stratus due to dry air. A bigger spread between observed and forecasted upper limit may indicate a dissolving process. Local dissipation effects like the Möhlin-Jet in the Basle-region are not considered.