Refer to figures.
The Mistral is a valley wind that flows down through the Rhône Valley in the French Alps. When high pressure forms in the Bay of Biscay, and low pressure in the Gulf of Genoa, the wind lines up roughly with the valleys of Southern France, which will channel the air, and use the Venturi effect (amongst other effects) to increase the wind speed, and change the direction of the air to flow along the valley, towards the Mediterranean Sea. It is usually a cold wind, and usually occurs in dry weather, giving clear skies and of course, strong winds.