Climate in Boston

The hottest month is July, with a mean temperature of 73.4 °F (23.0 °C). The coldest month is January, with a mean of 29.0 °F (−1.7 °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 13 days per year seeing the former extreme, and the most recent subzero reading occurring on January 24, 2011. The city averages roughly 95 nights per year with low temperatures at or below freezing. Extremes have ranged from −18 °F (−28 °C) on February 9, 1934, up to 104 °F (40 °C) on July 4, 1911.

Boston's coastal location on the North Atlantic moderates its temperature, but makes the city very prone to Nor'easter weather systems that can produce much snow and rain. The city averages 43.7 inches (1,110 mm) of precipitation a year, with 45.1 inches (115 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 moderating 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 fairly common, 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 breezes, 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