Chicago's climate is classified as hot-summer humid continental (Köppen Dfa), though lakefront areas like Northerly Island edge into a humid subtropical zone, with all four seasons distinctly represented and heavily influenced by nearby Lake Michigan. Winters are cold and snowy, with January averages around 31°F (-0.6°C) for highs and 16.5°F (-8.6°C) for lows, while seasonal snowfall averages 36 inches but has ranged from just 9.8 inches (1920–21) to 89.7 inches (1978–79). Summers are warm and humid, and precipitation is moderate and fairly even, with the driest months being January and February and the wettest being July and August. The official weather record dates back to 1870, though observations from that year and 1871 were lost in the Great Chicago Fire; Midway Airport began taking readings in 1928 and O'Hare Airport in 1958, with O'Hare now serving as the official station. Extreme winter temperatures have ranged from a record low of -27°F to a high of 75°F (set on February 27, 1976), and subzero readings occur on average 5.5 nights at Midway and 8.2 nights at O'Hare, though conditions can swing dramatically within a single week.