This report describes the typical weather at the Logan International Airport (Boston, Massachusetts, United States) weather station over the course of an average year. It is based on the historical records from 1974 to 2012. Earlier records are either unavailable or unreliable.
Boston, Massachusetts has a humid continental climate with hot summers and no dry season. The area within 25 mi of this station is covered by forests (51%), oceans and seas (26%), and built-up areas (21%).
Over the course of a year, the temperature typically varies from 22°F to 82°F and is rarely below 8°F or above 92°F.
The warm season lasts from June 5 to September 14 with an average daily high temperature above 73°F. The hottest day of the year is July 14, with an average high of 82°F and low of 67°F.
The cold season lasts from December 5 to March 14 with an average daily high temperature below 45°F. The coldest day of the year is January 19, with an average low of 22°F and high of 35°F.
The length of the day varies significantly over the course of the year. The shortest day is December 21 with 9:04 hours of daylight; the longest day is June 20 with 15:17 hours of daylight.
The earliest sunrise is at 5:06am on June 14 and the latest sunset is at 8:26pm on June 26. The latest sunrise is at 7:21am on November 3 and the earliest sunset is at 4:11pm on December 9.
Daylight savings time (DST) is observed in this location during 2012, starting in the spring on March 11 and ending in the fall on November 4.
The median cloud cover ranges from 58% (partly cloudy) to 80% (partly cloudy). The sky is cloudiest on April 27 and clearest on September 13. The clearer part of the year begins around July 3. The cloudier part of the year begins around November 14.
On September 13, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 58% of the time, and overcast or mostly cloudy 42% of the time.
On April 27, the cloudiest day of the year, the sky is overcast, mostly cloudy, or partly cloudy 70% of the time, and clear or mostly clear 30% of the time.
The probability that precipitation will be observed at this location varies throughout the year. Precipitation is most likely around January 4, occurring in 51% of days. Precipitation is least likely around September 13, occurring in 38% of days.
Over the entire year, the most common forms of precipitation are light rain, moderate rain, and light snow.
Light rain is the most severe precipitation observed during 34% of those days with precipitation. It is most likely around May 15, when it is observed during 23% of all days.
Moderate rain is the most severe precipitation observed during 19% of those days with precipitation. It is most likely around May 13, when it is observed during 13% of all days.
Light snow is the most severe precipitation observed during 15% of those days with precipitation. It is most likely around January 12, when it is observed during 21% of all days.
During the warm season, which lasts from June 5 to September 14, there is a 41% average chance that precipitation will be observed at some point during a given day. When precipitation does occur it is most often in the form of light rain (40% of days with precipitation have at worst light rain), moderate rain (23%), thunderstorms (22%), and heavy rain (10%).
During the cold season, which lasts from December 5 to March 14, there is a 49% average chance that precipitation will be observed at some point during a given day. When precipitation does occur it is most often in the form of light snow (36% of days with precipitation have at worst light snow), light rain (20%), moderate snow (13%), and moderate rain (11%).
The likelihood of snow falling is highest around January 13, occurring in 34% of days. The season in which it is relatively likely for snow to fall spans from November 16 to April 9.
During peak snow season, accumulation at this location on a given day is just less likely than not. The chances of there being snow on the ground are highest around January 30, occurring 39% of the time. The season in which snow is relatively likely to be on the ground spans from December 10 to March 21.
The snow is typically at its deepest on May 9, with a median depth of 11.6"; the depth exceeds 16.7" only one year out of ten.
The relative humidity typically ranges from 43% (comfortable) to 89% (very humid) over the course of the year, rarely dropping below 21% (dry) and reaching as high as 100% (very humid).
The air is driest around April 15, at which time the relative humidity drops below 56% (mildly humid) three days out of four; it is most humid around September 23, exceeding 83% (humid) three days out of four.
Dew point is often a better measure of how comfortable a person will find the weather than relative humidity because it more directly relates to whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid.
Over the course of a year, the dew point typically varies from 9°F (dry) to 67°F (muggy) and is rarely below -9°F (dry) or above 73°F (very muggy).
There are two periods in the year that are most comfortable: The first is between May 13 and July 11 and the second is between August 16 and October 13. The air feels neither too dry nor too muggy during these periods.
Over the course of the year typical wind speeds vary from 4 mph to 20 mph (light breeze to fresh breeze), rarely exceeding 28 mph (strong breeze).
The highest average wind speed of 13 mph (moderate breeze) occurs around March 5, at which time the average daily maximum wind speed is 20 mph (fresh breeze).
The lowest average wind speed of 10 mph (gentle breeze) occurs around August 5, at which time the average daily maximum wind speed is 16 mph (moderate breeze).