Mountain Climate - Mountain Geography: Physical and Human Dimensions - page 122

FOEHN WIND
Of all the transitory climatic phenomena of mountains, the foehn wind (pronounced
“fern” and sometimes spelled föhn) is the most intriguing. Legends, folklore, and mis-
conceptions have often arisen about this warm, dry wind that descends with great sud-
denness from mountains. The foehn, known in the Alps for centuries, is common to all
major mountain regions, formed as synoptic winds blow over a mountain crest and down
the lee side (Barry 2008). In North America, it is called the “Chinook” in the Yakima
Valley of eastern Washington, the “winawaay” in the Argentine Andes, the “zonda” in
southern California, the “Santa Ana” in New Zealand, the “Canterbury northwester” in
New Guinea, the “warm braw” in Japan, the “yamo oroshi” in the Barison Mountains of
Sumatra, the “bohorok” in Poland, the “halny wigtr” and in Romania, the “autru.” Other
mountain regions have their own local names for it as well (Brinkman 1971; Forrester
1982).
The foehn produces distinctive weather: gusts of wind, high temperatures, low hu-
midity, and very transparent and limpid air (Brinkman 1971; McGowan 2004). When
viewed through the foehn, mountains frequently take on a deep blue or violet tinge and
seem unnaturally close and high, because light rays are refracted upward through lay-
ers of cold and warm air. The bank of clouds that typically forms along the crest line is
associated with the precipitation failing on the windward side. This bank of clouds re-
mains stationary in spite of strong winds and is known as the foehn wall (when viewed
from the lee side).
FIGURE 3.27 Idealized cross section of wind movement in a valley with a glacier near its head. Glacier
wind is shown moving downslope in a thin zone immediately next to the ice. Valley wind blows
upslope and rides over the glacier wind. At elevations above the mountains the regional gradient
wind may be blowing in still another direction. (After Geiger 1965: 414.)
The primary characteristics of the foehn are a rapid rise in temperature, gustiness,
and an extreme dryness that puts stress on plants and animals and creates a fire hazard
(Brinkman 1971; Gaffin 2007). Forests, houses, and entire towns have been destroyed
during foehn winds clocked at up to 195 km/h (109 mi/h) (Reid and Turner 1997). For