Charleston has a humid subtropical climate , with mild winters, hot humid summers, and significant rainfall all year long. Summer is the wettest season; almost half of the annual rainfall occurs from June to September in the form of thundershowers. Fall remains relatively warm through the middle of November. Winter is short and mild, and is characterized by occasional rain. Measurable snow (≥0.1 in or 0.25 cm) occurs only several times per decade at the most, however freezing rain is more common; a snowfall/freezing rain event on January 3, 2018, was the first such event in Charleston since December 26, 2010. However, 6.0 in (15 cm) fell at the airport on December 23, 1989 during the December 1989 United States cold wave, the largest single-day fall on record, contributing to a single-storm and seasonal record of 8.0 in (20 cm) snowfall.
The highest temperature recorded within city limits was 104 °F (40 °C) on June 2, 1985, and June 24, 1944; the lowest was 7 °F (−14 °C) on February 14, 1899. At the airport, where official records are kept, the historical range is 105 °F (41 °C) on August 1, 1999, down to 6 °F (−14 °C) on January 21, 1985. Hurricanes are a major threat to the area during the summer and early fall, with several severe hurricanes hitting the area—most notably Hurricane Hugo on September 21, 1989 (a category 4 storm). The dewpoint from June to August ranges from 67.8 to 71.4 °F (19.9 to 21.9 °C).