Louisiana’s climate is subtropical, a natural result of its location on the Gulf of Mexico. As it also lies at the mouth of the vast Mississippi-Missouri river valley, roughly halfway between the Atlantic and the Pacific oceans, the state is also affected by continental weather patterns. Hot, humid summers, tempered by frequent afternoon thunder showers, alternate with mild winters. Louisiana is subject to tropical storms, and the hurricane season extends for six months, from June through November. Average annual temperatures range from 64 °F (18 °C) in the extreme north of the state to 71 °F (21 °C) at the mouth of the Mississippi River. The highest monthly average is 82 °F (28 °C) in July, and the lowest is 50 °F (10 °C) in January. In summer it is the humidity, rather than the heat, that is one of the more marked characteristics of the state’s subtropical climate. The frost season falls roughly between November 1 in northern Louisiana and December 14 in the extreme southeast. The average growing season ranges from 220 to 320 days and the average precipitation ranges from almost 45 inches (1,140 mm) at Shreveport to more than 56 inches (1,420 mm) at New Orleans.