This report describes the typical weather at the Boise Air Terminal (Gowen Field) (Boise, Idaho, 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.
Boise, Idaho has a cold semi-arid steppe climate. The area within 25 mi of this station is covered by shrublands (36%), grasslands (35%), croplands (15%), and forests (11%).
Over the course of a year, the temperature typically varies from 22°F to 92°F and is rarely below 7°F or above 100°F.
The warm season lasts from June 16 to September 9 with an average daily high temperature above 81°F. The hottest day of the year is July 27, with an average high of 92°F and low of 62°F.
The cold season lasts from November 18 to February 20 with an average daily high temperature below 46°F. The coldest day of the year is December 28, 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 8:57 hours of daylight; the longest day is June 20 with 15:25 hours of daylight.
The earliest sunrise is at 6:03am on June 14 and the latest sunset is at 9:31pm on June 27. The latest sunrise is at 8:24am on November 3 and the earliest sunset is at 5:08pm 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 0% (clear) to 84% (mostly cloudy). The sky is cloudiest on January 2 and clearest on August 7. The clearer part of the year begins around April 26. The cloudier part of the year begins around November 5.
On August 7, the clearest day of the year, the sky is clear, mostly clear, or partly cloudy 88% of the time, and overcast or mostly cloudy 12% of the time.
On January 2, the cloudiest day of the year, the sky is overcast, mostly cloudy, or partly cloudy 67% of the time, and clear or mostly clear 32% of the time.
The probability that precipitation will be observed at this location varies throughout the year. Precipitation is most likely around December 27, occurring in 53% of days. Precipitation is least likely around August 4, occurring in 17% of days.
Over the entire year, the most common forms of precipitation are light rain, light snow, moderate rain, and thunderstorms.
Light rain is the most severe precipitation observed during 40% of those days with precipitation. It is most likely around April 7, when it is observed during 20% of all days.
Light snow is the most severe precipitation observed during 24% of those days with precipitation. It is most likely around January 5, when it is observed during 28% of all days.
Moderate rain is the most severe precipitation observed during 16% of those days with precipitation. It is most likely around May 5, when it is observed during 9% of all days.
Thunderstorms are the most severe precipitation observed during 11% of those days with precipitation. They are most likely around July 12, when it is observed during 8% of all days.
During the warm season, which lasts from June 16 to September 9, there is a 19% 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 (43% of days with precipitation have at worst light rain), thunderstorms (40%), and moderate rain (15%).
During the cold season, which lasts from November 18 to February 20, there is a 50% 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 (46% of days with precipitation have at worst light snow), light rain (26%), moderate snow (12%), and moderate rain (11%).
The likelihood of snow falling is highest around January 5, occurring in 36% of days. The season in which it is relatively likely for snow to fall spans from November 7 to March 25.
Either snow rarely accumulates at this location or snow depth measurements are unavailable or unreliable.
The relative humidity typically ranges from 17% (dry) to 90% (very humid) over the course of the year, rarely dropping below 11% (very dry) and reaching as high as 99% (very humid).
The air is driest around July 26, at which time the relative humidity drops below 20% (dry) three days out of four; it is most humid around January 13, exceeding 85% (very 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 16°F (dry) to 50°F (dry) and is rarely below 2°F (dry) or above 57°F (comfortable).
Over the course of the year typical wind speeds vary from 0 mph to 17 mph (calm to moderate breeze), rarely exceeding 24 mph (strong breeze).
The highest average wind speed of 9 mph (gentle breeze) occurs around March 25, at which time the average daily maximum wind speed is 17 mph (moderate breeze).
The lowest average wind speed of 7 mph (light breeze) occurs around January 13, at which time the average daily maximum wind speed is 12 mph (moderate breeze).