The Foehn Gap

Figure 2: Foehn gap over the northern parts of Switzerland (red arrow). MSG HRV from 21 January, 2005 at 12:15 UTC.

The Foehn gap on the lee side of the mountain barrier is located at the wave trough (figure 2). The width of the Foehn gap is given by the wave length of the lee waves; wave amplitude (and not length) usually decreases rapidly downstream of the mountains.