Metropolitan City of Cagliari the warmest month with an average temperature of that of about . African anticyclone activity can cause heat waves starting in June. From mid-June to mid-September rain is rare and appears in afternoon storms. The rainy season starts in September, but the first cold days come in December, usually the wettest month. Winds are frequent, especially the mistral and sirocco; in Summer days a marine sirocco breeze ("s'imbattu") lowers the temperature and the humidity. On the surrounding mountains, the climate is very different with plentiful average rainfall, cold winters, and mild warm summers (Csb in the Köppen climate classification). As
Mistral (wind) reputation for making the sky especially clear. There is also, however, the mistral noir, which brings clouds and rain. The mistral noir occurs when the Azores High is extended and draws in unusually moist air from the northwest. The long and enclosed shape of the Rhône Valley, and the Venturi effect of funnelling the air through a narrowing space, is frequently cited as the reason for the speed and force of the mistral, but the reasons are apparently more complex. The mistral reaches its maximum speed not at the narrowest part of the Rhône Valley, south of Valence, but much