Climate

South Carolina’s climate is classified as humid subtropical, which is typical of middle-latitude locations situated on eastern margins of large continents. Rainfall is abundant and distributed fairly evenly throughout the year. There is a seasonal variation in temperatures ranging from hot and humid summers to mild winters with some below-freezing temperatures. Within this general framework, however, climate varies considerably across the state.

Most of the state receives between forty-six and fifty inches of rain annually, but Caesars Head in the Blue Ridge region averages seventy-nine inches. Temperatures generally decrease from the coastal plain to the Blue Ridge, as illustrated by the mean and the mean daily minimum temperatures for Charleston, Columbia, and the Greenville/Spartanburg areas (see table). Summers tend to be hot across the state, but Columbia and the Midlands area tend to have higher July temperatures.

Rainfall provides almost all of the precipitation, but snow, sleet, and hail occasionally do occur. Precipitation is recorded in each month, but there is seasonal variation. Frequent and sometimes violent late afternoon and early evening convectional thunderstorms are characteristic of summer. These storms are generally brief, but rainfall can be heavy with high winds, thunder, and lightning. Frontal precipitation is common during the winter and can include snow or sleet but usually is characterized by heavy cloud cover with drizzle or steady rain that can last for hours. These different rainfall types along with temperature variations represent South Carolina’s annual cycle of climatic variation.

Winter normally is typified by the presence of cold, dry continental air masses making December, January, and February the three coldest months. On occasion, two to five times per year, polar air masses can invade the state, bringing very cold temperatures for several days. A typical cold-front scenario begins with warm, moist air; cloudy skies; and southerly winds. As the front approaches, the sky becomes gray with clouds, and precipitation begins first as drizzle and then becomes heavy rain. Temperatures drop as the rain continues. The heavy rain then gives way to drizzle, the sky clears, and northerly winds dominate. Southerly winds often follow, bringing in maritime air from the Caribbean and South Atlantic, and mild temperatures. Coastal temperatures are moderated by the Atlantic Ocean and the warm Gulf Stream, while the higher elevations of the upper Piedmont and Blue Ridge experience colder temperatures. Charleston, for example, has a higher mean daily minimum temperature than either Columbia or the Greenville/Spartanburg area.

Snowfall is rare along the coast–about once every three years– and is more common in the upper Piedmont and Blue Ridge. Except for those in the Blue Ridge region, accumulations usually melt away in a day or two. February is statistically the snow month. The record snowfall occurred in February 1973, with twenty-four inches recorded at Rimini, sixteen inches at Columbia, seven inches at Charleston, and little or no snowfall in the upstate. Even light snowfalls can disrupt traffic, and schools, offices, and businesses often close. Occasional ice storms also create severe road problems and power outages.

Spring is a transition season from low winter temperatures and frontal precipitation to high temperatures and convectional rainfall characteristic of summer. The number of cold fronts diminishes as continental air masses are replaced by warmer maritime tropical air. Similarly, the cloudy and steady rain caused by passing cold fronts is replaced by the puffy cumulus clouds and thunderstorms associated with convectional precipitation during March, April, and May. These changing atmospheric conditions are favorable for the development of tornadoes.

Tornadoes form during all seasons of the year, but about one-third the annual total is recorded in April and May. South Carolina averages about ten tornadoes a year. A series of tornadoes passing through two corridors between Anderson and York Counties and across the Midlands from Aiken to Florence Counties left 77 people dead and 800 injured on April 30, 1924. More recently, 21 people died and 448 were injured when eight or nine separate tornadoes swept through the lower Piedmont from McCormick to Marlboro Counties on March 28, 1984.

Summer’s hot and humid weather prevails from June through August, and the heat is relatively unbroken. Contrasting with winter, temperatures are about the same across much of the state except for cooler temperatures at higher elevations of the Blue Ridge region. The single most important factor influencing South Carolina’s summer weather is the Bermuda high, an extremely large subtropical high-pressure cell centered over the Atlantic. Its clockwise circulation normally causes a southerly flow of warm and humid maritime tropical air over the state, resulting in high temperatures and the necessary moisture for convectional thunderstorms. These thunderstorms account for about one-third of the annual rainfall, making summer the wettest season of the year.

The Bermuda high, however, sometimes stalls or becomes stationary off the coast, and its stable subsiding air can prevent the normal convection process. This stymies cloud and thunderstorm development, causing hot sunny days and stagnant air conditions. Sometimes these dry conditions last for weeks or even months, causing droughts. July is usually Columbia’s wettest month with a mean 5.54 inches of rainfall. But only 0.57 of an inch was recorded in July 1973.

Fall, like spring, is a transitional season. Temperatures slowly become cooler, and the high humidity of summer wanes between September and November. Dry continental air masses become more frequent. Because there is less water vapor in the atmosphere, the state receives only about twenty percent of its annual precipitation in the fall. October and November are statistically the two driest months of the year. Nearly one-half of all fall days are warm and sunny with bright blue skies. Since there is little cloud cover, nights are cool to cold. The rapid cooling of the earth’s surface often results in fog during the night and early morning hours.

Hurricanes are most common in early fall and late summer, and September poses the greatest threat. Damage along the coast is caused by the winds, but most death and destruction results from flooding. The deadliest hurricane to date struck Beaufort in August 1893, and an estimated two thousand people died. Hurricane Hazel hit the Myrtle Beach area in October 1954 with a storm surge estimated at seventeen feet, which washed away oceanfront dunes, destroyed fishing piers, and damaged houses. Hurricane Hugo struck Charleston at high tide with a fifteen-to twenty-foot storm surge and raced inland in September 1989. Winds, clocked at 138 mph with gusts of more than 160 mph, and flooding caused twenty-six deaths and left fifty thousand to seventy thousand homeless. Damage was estimated at more than $6 billion.

Kovacik, Charles F., and John J. Winberry. South Carolina: The Making of a Landscape. 1987. Reprint, Columbia: University of South Carolina Press, 1989.

Purvis, John C., Wes Tyler, and Scott F. Sidlow. General Characteristics of South Carolina’s Climate. Columbia: South Carolina State Climatology Office, [1990].