The climate of Salt Lake City, Utah features cold and snowy winters, hot and dry summers, and modest to light seasonal rainfall. Lying in the Salt Lake Valley, the city is surrounded by mountains and the Great Salt Lake. Under the Köppen climate classification, Salt Lake City has either a Mediterranean climate (Csa) or dry-summer continental climate (Dsa) depending on which variant of the system is used, though it borders on a cold semi-arid climate (BSk) due to the city's relatively low precipitation. The city has four distinct seasons: a cold, snowy winter; a hot, dry summer; and two relatively wet transition periods. The Pacific Ocean is the primary influence on the weather, contributing storms from about October to May, with spring being the wettest season. Snow falls frequently during the winter, contributed largely by the lake-effect from the Great Salt Lake. The only source of precipitation in the summer is monsoon moisture moving north from the Gulf of California. Summers are hot, frequently reaching above , while winters are cold and snowy. The Rocky Mountains to the east and north usually block powerful polar highs from affecting the state during the winter. Temperatures rarely fall below , but frequently stay below freezing. Temperature inversions during winter can lead to thick overnight fog and daytime haze in the valley as cool air, moisture, and pollutants are trapped in the valley by surrounding mountains. Overview Temperatures Winter temperatures are not as extreme as might be expected, given the elevation and latitude (40°45'N) of the city. The Rocky Mountains to the east and northeast of the state block most cold waves from polar highs positioned in the Great Plains from reaching the city. The frigidly cold air that does affect the city must come directly from the north or north-northwest from western Canada through fewer and lower intervening mountains. Temperatures seldom fall below ; Salt Lake City has experienced sub-zero temperatures during only 4 storm cycles in the last 10 years. However, the average sub-zero days in a year is 2. Salt Lake City averages 26 days with high temperatures at or below freezing. In winter, warm air from the surrounding Desert Southwest is usually only drawn up to the city in advance of a cold front arriving from the northwest. January is the coldest month with an average temperature of . Salt Lake City's record low maximum temperature is , set