Climate of New York - Precipitation

Precipitation

Average precipitation across the region show maxima within the mountains of the Appalachians. Between 28 inches (710 mm) and 62 inches (1,600 mm) of precipitation falls annually across the Northeastern United States, and New York's averages are similar, with maxima of over 60 inches (1,500 mm) falling across southwestern Lewis county, northern Oneida county, central and southern Hamilton county, as well as northwestern Ulster county. The lowest amounts occur near the northern borders with Vermont and Ontario, as well as much of southwestern sections of the state. Temporally, a maximum in precipitation is seen around three peak times: 3 a.m., 10 a.m., and 6 p.m. During the summer, the 6 p.m. peak is most pronounced.

Coastal extratropical cyclones, known as nor'easters, bring a bulk of the wintry precipitation to the region during the cold season as they track parallel to the coastline, forming along the natural temperature gradient of the Gulf stream before moving up the coastline. The Appalachian Mountains largely shield New York City from picking up any lake-effect snow, which develops in the wake of extratropical cyclones downwind of the Great Lakes. The Finger Lakes of New York are long enough for lake-effect precipitation. Lake-effect snow from the Finger Lakes (like elsewhere) occurs in upstate New York until those lakes freeze over. Annual average lake-effect snows exceed 150 inches (380 cm) downwind of Lake Erie and 200 inches (510 cm) downwind of Lake Ontario.

During the summer and early fall, mesoscale convective systems can move into the area from Canada and the Great Lakes. Tropical cyclones and their remains occasionally move into the region from the south and southwest. The region has experienced a couple heavy rainfall events that exceeded the 50-year return period, during October 1996 and October 1998, which suggest an increase in heavy rainfall along the coast.