Under the Köppen climate classification, Philadelphia falls in the northern periphery of the humid subtropical climate zone (Köppen Cfa). Summers are typically hot and muggy, fall and spring are generally mild, and winter is cold. Snowfall is highly variable, with some winters bringing only light snow and others bringing several major snowstorms, with the normal seasonal snowfall standing at 22.4 in (57 cm); snow in November or April is rare, and a sustained snow cover is rare. Precipitation is generally spread throughout the year, with eight to twelve wet days per month, at an average annual rate of 41.5 inches (1,050 mm), but historically ranging from 29.31 in (744 mm) in 1922 to 64.33 in (1,634 mm) in 2011. The most rain recorded in one day occurred on July 28, 2013, when 8.02 in (204 mm) fell at Philadelphia International Airport.