Outflow Winds Can Make Winters More Miserable
Where do these strong cold winds come from, and how do they form?
Outflow winds are a second group of local winds, of similarsignificance to the Foehn Winds
and Pre-frontal Winds
described elsewhere. For some background information, visit Introduction To Winds
Outflow winds are characteristically cold winds which sweep down from elevated mountainous or plateau areas to make lifemiserable (or invigorating) for those living in the warmer,often coastal lowlands.
The most famous of them are the Mistral and Bora of eastern and western Europe respectively, but similar winds such as the Tramontana of Italy, the Vardar of Macedonia, and the Burda or Purga of Central Asia, Siberia and Alaska are similar.
The Mediterranean examples are well known because of the rapid cooling that defines them, and the frequently associated sleet and rain. They are related to polar outbursts, but aredistinguished by their origin in somewhat lower latitudes.
Many of these winds are also Gap Winds - strong windsaccentuated by their passage through low points in mountainranges. Here the wind is concentrated through the pass andspeeds up considerably. Its greatest effects are feltfor some distance down the valley.
Winds like this can also create havoc over small areas of the sea downwind from the gaps, a common feature of several parts of the Mediterranean.
Although Outflow Winds share some features of the Foehns, particularly in their downslope or katabatic flow, theyoriginate in colder areas and move to warmer ones. They also tend to blow from less elevated areas to the high ranges which foehn winds have to cross, so their general effect is falling rather than rising temperatures.
Perhaps the best developed of all outflow winds is unnamed.
It occurs in Antarctica and begins as a cold high pressure
air mass over the South Pole - a plateau at around
10,000 feet (3,000m). This super cold air blows at
great speeds down the glacial valleys leading to the
coast, and was one of the major challenges faced by early
There are two interesting variants of these winds. One occurs
when cold air accumulates in a mountain or plateau basin. Being
heavy, it occupies the lower altitudes, but when there is enough of it to fill the basin it overflows and moves down available
passes as a strong cold gap wind.
Another relative is the Williwaw - a Canadian or Alaskan wind
whose name has been transplanted to other parts of the world.
It is characterised by very strong downbursts of wind on the
lee side of a coastal mountain. It has some characteristics of
a foehn, in that the wind itself develops on the other side of the range, but little of the warmth. It may also be a rotor
type wind, resulting from eddies caused by the wind being disrupted by the intervening mountains.
Other major types of local winds, described elsewhere, are the
Foehn Winds and
Pre-frontal Winds, while more general characteristics of winds can be found in the
Introduction To Winds pages.
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Last update 05/28/2011