Charleston has a humid subtropical climate (Köppen climate classification Cfa), 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 November. Winter is short and mild, and is characterized by occasional rain. Measurable snow (≥0.1 in or 0.25 cm) only occurs several times per decade at the most, with the last such event occurring December 26, 2010. However, 6.0 in (15 cm) fell at the airport on December 23, 1989, the largest single-day fall on record, contributing to a single-storm and seasonal record of 8.0 in (20 cm) snowfall.