Mississippi’s climate is controlled by the North American land mass to the north, the state’s subtropical latitude, and the Gulf of Mexico to the south. These controls produce the humid subtropical climate type, typified by mostly mild winters without extended periods of below-freezing temperatures; long, hot summers; and no routine wet or dry seasons.
Throughout much of the year prevailing southerly winds result in semitropical conditions. High humidity, combined with hot days and nights, generally produces discomfort during the warm season, with dew point temperatures routinely in the upper 70s. In the colder season the state’s weather is dominated by the positions of the polar and subtropical jet streams, which control warm and cold fronts that alternately subject the state to warm tropical air and cold continental air. Cold spells seldom last more than three or four days, and the ground rarely freezes. Continental polar and Arctic air masses occasionally cause extreme cold spells, including a record low temperature of −19 F. Conversely, warm fronts regularly raise temperatures into the 80s during January and February.
Daily maximum and minimum temperatures in January average about 50 F and 30 F in the north and about 61 F and 43 F along the coast. July daily average highs are about 93 F and 90 F in the north and on the coast, respectively. July daily minimum temperatures average about 70 F (north) and 75 F (south). Temperatures of 90 F or higher occur an average of just fifty-five days per year on the coast, where the Gulf waters have a cooling effect. However, the number of days 90 F or higher rapidly increases inland, topping one hundred about fifty miles from the water. Temperatures of 32 F or lower occur on average about thirteen days a year on the immediate Gulf Coast and about seventy-three days per year on the Tennessee border.
Temperatures exceed 100 F each summer, with a record high for the state of 115 F. Temperatures below zero occur an average of once every five years, though below-freezing temperatures occur every winter throughout the state. Last freeze dates are quite variable, averaging from 3 April in the north to 20 February along the coast.
Mean annual precipitation ranges from about fifty inches along the northern border to about sixty-five inches along the coast and averages about fifty-six inches statewide. Irrigation is becoming increasingly common because rainfall, though abundant, does not always come when it is most needed. Mississippi commonly experiences general agricultural droughts, especially during the summer season. Stream flow and precipitation records indicate at least nine significant periods of extended drought since 1930.
Snow and other forms of winter precipitation are not as rare in Mississippi as is generally believed. Measurable snow or sleet falls on some part of the state in about 95 percent of all years. Many individual snow events of as much as twelve inches have been recorded in the northern part of the state. Ice storms occur about once every four years in the northern half of the state and about once every thirteen years in the southeastern part of the state.
Thunderstorms occur on an average of fifty to sixty days a year in the northern section of the state and seventy to eighty days a year near the coast. Tropical storms and hurricanes pose a hazard to life and property and generally come from the south. These systems weaken quickly when they pass over land, so damage in Mississippi is confined mainly to the coastal areas, while losses further inland generally result from rain damage to crops and from floods.
Mississippi also commonly experiences tornadoes. The state ranks twelfth nationally in number of reported tornadoes and eighth in number of tornadoes per ten thousand square miles. Unfortunately, the state ranks first nationally in tornado deaths per one million population. About two-thirds of the state’s tornadoes occur between February and May, but they can come throughout the year.
- John L. Baldwin, Climates of the United States (1973)
- James R. Fleming, Meteorology in America, 1800–1870 (1990)
- Cary J. Mock, in Hurricanes and Typhoons: Past, Present, and Future, ed. Richard J. Murnane and Kam-biu Liu (2004)
- Edgar T. Thompson, Agricultural History (January 1941)