The forecasted pressure gradient (unit hectopascal, hPa) between Lugano and Zurich shows the flow over the Alps. If we have a positive pressure gradient, that means the surface pressure in Zurich is lower than in Lugano, south foehn comes up in Liechtenstein (wind from south). The intensity of foehn winds increases with larger pressure gradients.
Empirically we need at least a pressure gradient of 4 hPa for the breakthrough of foehn winds in the alpine valleys and at least 8 hPa for the breakthrough in the adjacent lowland.
The forecast is based on model output statistics (MOS) by MeteoGroup and is updated every hour.