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Definition:
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Name given to cold northerly, northeasterly, or easterly, postfrontal winds in the Swiss Middleland (the region between the Jura and the Alps) and in various regions of eastern France. The bise is typically driven by an anticyclone building to the northwest or north of the Alps. According to Wanner and Furger (1990), "the cold air flow from the north and northeast is channeled between the Jura and the Alps and leads to the formation of the bise over the Swiss Middleland and the upper Rhône Valley. Thus, the bise is normally a postfrontal phenomenon and is closely connected with the advection of cold and dry continental air. Typically the classic bise endures about one to three days." The bise is most frequent in spring, when it usually brings fine, bright weather. In winter a special case of the bise occurs when the pressure gradient is produced by a Mediterranean cyclone system to the south of the Alps, bringing moist air in from the Balkans. Accompanied by heavy clouds, snow whirlwinds in the mountains, and rain, snow, or hail, this wind is called a "black bise" (bise noire in Switzerland and Saône in east central France; bise nègre in Aveyron in south central France). In spring the bise can last for several days and bring damaging frosts. In the Morvan in east central France the very dry bise in March is termed hale de mars (drying wind of March). In the Drôme Valley southeast of Valence (southeast France) the name bise brume is given to a moist, mild, and sometimes foggy wind from the northwest. (Also spelled bize.)
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