Winnipeg lies in the middle of the North American continent on a low-lying, flat plain. Due to its location in the Canadian Prairies, and its distance from both mountains and oceans, it has an extreme humid continental climate (Köppen "Dfb", Plant Hardiness Zone 3b-4a), in that there are great differences between summer and winter temperatures. The openness of the prairies leaves Winnipeg exposed to numerous weather systems including blizzards and cold Arctic high pressure systems, known as the polar high. Winnipeg has four distinct seasons, with short transitional periods between winter and summer.