From AMS Glossary
A characteristic deformation of isobars on a surface synoptic weather chart during a well-developed foehn.
The flow produces a pressure ridge over and just windward of the mountain range and a lee trough on the downwind side. The isobars bulge correspondingly, giving a noselike profile in the pressure ridge over the mountains. This configuration is prominent and characteristic of the foehn over the Alps, but over the Rocky Mountains the ridge pattern is less pronounced (perhaps because of the more complicated upstream orography or the presence of cold-air layers, which obscure the surface-pressure pattern, in the valleys of the western United States).