Climate of Boston

Boston has a climate that is continental in nature but with maritime influences owing to its coastal location, a phenomenon common to coastal southern New England. The climate is classified as a humid continental climate (Koppen Dfb with areas of Dfa). Summers are typically warm, rainy, and humid, while winters are cold, windy, and snowy. Spring and fall are usually mild, but conditions are widely varied, depending on wind direction and jet stream positioning. Prevailing wind patterns that blow offshore affect Boston, minimizing the influence of the Atlantic Ocean.

The hottest month is July, with a mean temperature of 73.9 °F (23.3 °C). The coldest month is January, with a mean of 29.3 °F (−1.5 °C). Periods exceeding 90 °F (32 °C) in summer and below 10 °F (−12 °C) in winter are not uncommon but rarely extended, with about 14 days per year seeing the former extreme, and the most recent subzero reading occurring on January 24, 2011. Extremes have ranged from −18 to 104 °F (-28 to 40 °C), recorded on February 9, 1934 and July 4, 1911, respectively.

Sunset at Charles River in December 2010

Boston's coastal location on the North Atlantic, although it moderates temperatures, also makes the city very prone to Nor'easter weather systems that can produce much snow and rain. The city averages 42.5 inches (1,080 mm) of precipitation a year, with 41.8 inches (106 cm) of snowfall a year. Snowfall increases dramatically as one goes inland away from the city (especially north and west of the city)—away from the warming influence of the ocean. Most snowfall occurs from December through March. There is usually little or no snow in April and November, and snow is rare in May and October.
Fog is prevalent, particularly in spring and early summer, and the occasional tropical storm or hurricane can threaten the region, especially in early autumn. Due to its situation along the North Atlantic, the city is often subjected to sea breeze, especially in the late spring, when water temperatures are still quite cold and temperatures at the coast can be more than 20 °F (11 °C) colder than a few miles inland, sometimes dropping by that amount near midday. From May to September, the city experiences thunderstorms that are occasionally severe; large hail, damaging winds and heavy downpours accompany such severe events. Although downtown Boston has never been struck by a violent tornado, the city itself has seen its fair share of tornado warnings, but damaging storms are more common to areas north, west, and northwest of the city.



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