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Mistral (wind)

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The Mistral in France is a cold, strong, and usually dry wind, usually occurring in the winter and spring, blowing from the northwest or north of Europe through the valley of the Rhône River to the Mediterranean., It also affects the whole of Sardinia in Italy.

The name comes from the Languedoc dialect of the provençal language. and means "masterly." The same wind is called "mistrau" in the occitan language, "mestral" in Catalan and "maestrale" in Italian and Corsican.

The mistral is usually accompanied by clear and sunny weather, and it plays an important role in creating the climate of Provence. It can reach speeds of ninety kilometers an hour, particularly in the Rhone Valley.

The Cause of the mistral

The mistral is an example of a katabatic wind, which is created by the difference in pressure between the cold air of a high pressure system over the Atlantic or northwest Europe and a low pressure system over the Gulf of Lion or the Gulf of Genoa in the Mediterranean. The high-pressure air flows south through the Rhone Valley, gathering speed as it is funneled between the Alps and the Massif Central.

In France, the mistral particularly affects Provence, Languedoc east of Montpellier, and the Var Deparment to the west of Frejus, as well as all of the Rhone Valley from Lyon to Marseille. The mistral usually blows from northwest or north, but in certain pre-alpine valleys and along the Cote d'Azur, the wind is channelled by the mountains so that it blows from east to west. Sometimes it also blows from the north-north-east toward the east of Languedoc as far as Cap Béar. Frequently the mistral will affect only one part of the region, particularly when it is not caused by a flow of air from the northwest.

The mistral from the northwest

The mistral and the other similar north wind in France, the tramontane, usually originate with a flow of air from the northwest. A cold front associated with a low pressure area over northern Europe moves toward the east. The flow shifts to the northwest, carrying cold ocean air. The cool wind from the northeast dries the air and rapidly disperses the clouds. The acceleration of the wind is caused by the creation of a depression, or low-pressure area, in the Gulf of Genoa under the wind from the Alps. In this case the mistral affects the entire Rhone Valley, the inland territory of Provence and the Cote d'Azur, where the wind comes from the east.

In the Languedoc area, where the tramontane is the strongest wind, the mistral and the tramontane blow together onto the Gulf of Lion and the northwest of the western Mediterranean, and can be felt to the east of the Balearic Islands, in Sardinia, and sometimes as far as the coast of Africa.

The mistral from the northeast

When the flow of air comes from the northeast due to a widespread low pressure area over the Atlantic and atmospheric disturbances over France, the air is even colder at both high altitudes and ground level, and the mistral is even stronger, and the weather worse, with the creation of cumulus clouds bringing weak storms. This kind of mistral is weaker in the east of of Provence and the Cote d'Azur.

The mistral from the west

When the mistral originates from the west, the mass of air is not so cold and the wind only affects the plain of the Rhone delta and the Cote d'Azur. The good weather is confined to the coast of the Mediterranean, while it can rain in the interior. The Cote d'Azur generally has a clear sky and warmer temperatures, the classic effect of this type of Foehn Wind. This type of mistral usually blows for no more than one to three days.

The mistral from the northeast

The mistral originating from the northeast has a very different character; it is felt only in the west of Provence and as Montpellier, with the wind coming from either the north or north-northeast. In the winter this is by far the coldest form of the mistral, when it carries chill air from Central Europe and from Russia. It is caused by the presence of a high pressure area over northern Europe. The wind can blow for more than a week, until the high pressure area has moved east and the wind changes direction. This kind of mistral is often connected with a low pressure area in the Gulf of Genoa, and it can bring unstable weather to the Cote d'Azur and the east of Provence, sometimes bringing heavy snow to low altitudes in winter.

The summer mistral

The summer mistral, unlike the others, is created by purely local conditions. It usually happens in July, and only in the valley of the Rhone and on the coast of Provence. It is caused by a thermal depression over the interior of Provence (The Var and Alpes de Haute-Provence), created when the land is overheated. This creates a flow of air from the north toward the east of Provence. This wind is frequently cancelled out close to the coast by the breezes from the sea. It does not blow for more than a single day, but it is feared in Provence, because it dries the vegetation and it can spread forest fires

The mistral from the east

The mistral does not always bring good weather. When a low pressure front over the Mediterranan approaches the coast from the southeast, the weather can change quickly for the worse, and the mistral and its clear sky changes rapidly to an east wind bringing rain and threatening clouds. The position of the low-pressure front creates a flow of air from the northwest or the northeast. pouring through the Rhone Valley. If this low-pressure area moves back toward the southeast, the mistral will quickly clear the air and the good weather will return; but if the cold-weather front continues to approach the land, bad weather will continue for several days in the entire Mediterranean basin, sometimes transforming into what French meteorologists call an épisode cévenol, a period of torrential rains and floods, particularly in the areas west of the Rhone Valley: the Ardeche, the Gard, Herault and Lozere.

The Effects of the Mistral

Sunshine, clarity, and a dry climate

The mistral is a dry wind, and its arrival almost always clears the skies and dries the air. The Mistral helps explain the unusually sunny climate of Provence (2700 to 2900 hours of sunshine a year). When other parts of France have clouds and storms, Provence is rarely affected for long, since the mistral quickly clears the sky. In less than two hours, the sky can change from completely covered to completely clear. The mistral also blows away the dust, and makes the air particularly clear, so that during the mistral it is possible to see mountains 150 kilometers and farther away.

The mistral and health

The mistral has the reputation of bringing good health, since the dry air dries stagnant water and the mud, giving the mistral the local name 'mange-fange' (eng. "mud-eater.") It also blows away pollution from the skies over the large cities and industrial areas.

The mistral and forest fires

The sunshine and dryness brought by the mistral have an important effect on the local vegetation. The vegetation in Provence, which is already dry because of the small amount of rainfall, is made even drier by the wind, which makes it particularly susceptible to fires, which the wind spreads very rapidly, sometimes devasting large areas before anyone can stop them. During the summer, thousand of hectares normally burn when the mistral is blowing.

The mistral and the growth of vegetation

In the Rhone Valley and on the plain of la Crau, the regularity and force of the mistral causes the trees to lean toward the south. When the forest disappears. the strong wind makes it difficult for new trees to grow. The farmers of the Rhone Valley have long planted rows of cypress trees to shelter their crops from the dry force of the mistral. The mistral can also have beneficial effects- the moving air can save crops from the spring frost, which can last until the end of April.

The chilling of the sea

As summer visitors to the beach in Provence learn, the summer mistral can quickly lower the temperature of the sea, as the wind pushes the warm water near the surface out to sea and it is replaced by colder water from greater depths.

The effects of the mistral beyond France

The mistral can effect the weather in North Africa, Sicily and Malta or throughout the Mediterranean, particularly when low pressure areas form in the Gulf of Genoa.

The same name is used for the cool North/North-West wind in the Adriatic Sea. This is also a katabatic wind and has similar causes as its French namesake - air cooled over the Dinaric Alps flows down into the Adriatic sea, where it is known as Maestro or Maestral.

In south-western Crete it is known as Maestro and it is considered the most beneficial wind, which is said to blow only during the daytime.

The Mistral in Provencal Culture

The Mistral plays an important part in the life and culture of Provence, in the south of France. The Mas (Provencal Farmhouse) traditionally faces south, with its back to the Mistral. The bell towers of villages in Provence are often open iron frameworks, which allow the wind to pass through. The traditional Provençal Christmas creche often has a figure of a shepherd holding his hat, with his cloak blowing in the Mistral.

Sources and Citations

This article is largely an edited version of the articles from the French-language Wikipedia: Mistral (vent) and Vents de France.

Jean Vialar, Les vents régionaux et locaux, 1948, réédité par Météo-France en 2003

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