Because January averages 29.5 °F (-1.4 °C), New York has a humid continental climate according to the Köppen climate classification; the northernmost city on the Eastern Seaboard without this classification is Philadelphia. New York City has cold winters but the city's coastal position keeps temperatures slightly warmer than inland regions, helping to moderate the amount of snow which averages 25 to 35 inches (63.5 to 88.9 cm) each year. New York City has a frost-free period lasting an average of 199 days between seasonal freezes. Spring and autumn in New York City are erratic, and can range from cold and snowy to hot and humid, although they can also be cold or cool and rainy. Summer in New York City is hot and humid, with temperatures of 90 °F (32 °C) or higher recorded on average 18 to 25 days each summer. Though not usually associated with hurricanes, New York City is susceptible to them, notably the 1821 Norfolk and Long Island hurricane which flooded southern Manhattan, and the New England Hurricane of 1938, which brushed the eastern end of the city. The city's long-term climate patterns have been affected by the Atlantic Multidecadal Oscillation, a 70-year-long warming and cooling cycle in the Atlantic that influences the frequency and severity of coastal storms in the region.
