Outflow Winds

Outflow Winds Can Make Winters More Miserable

Where do these strong cold winds come from, and how do they form?

Outflow Winds

Outflow winds are a second group of local winds, of similar significance 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 life miserable (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 are distinguished by their origin in somewhat lower latitudes.

Many of these winds are also Gap Winds - strong winds accentuated by their passage through low points in mountain ranges. Here the wind is concentrated through the pass and speeds up considerably. Its greatest effects are felt for 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, they originate 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 polar explorers.

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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