December Weather in Boise Idaho, United States
Daily high temperatures decrease by 6°F, from 42°F to 36°F, rarely falling below 24°F or exceeding 53°F.
Daily low temperatures decrease by 5°F, from 29°F to 24°F, rarely falling below 10°F or exceeding 41°F.
For reference, on July 26, the hottest day of the year, temperatures in Boise typically range from 63°F to 93°F, while on January 1, the coldest day of the year, they range from 24°F to 36°F.
Average High and Low Temperature in December in Boise
The figure below shows you a compact characterization of the hourly average temperatures for the quarter of the year centered on December. The horizontal axis is the day, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.
Average Hourly Temperature in December in Boise
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
The month of December in Boise experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 57% throughout the month.
The clearest day of the month is December 12, with clear, mostly clear, or partly cloudy conditions 44% of the time.
For reference, on January 10, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 59%, while on July 28, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 83%.
Cloud Cover Categories in December in Boise
0% clear 20% mostly clear 40% partly cloudy 60% mostly cloudy 80% overcast 100%
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Boise, the chance of a wet day over the course of December is gradually decreasing, starting the month at 28% and ending it at 25%.
For reference, the year's highest daily chance of a wet day is 28% on December 1, and its lowest chance is 3% on July 28.
Over the course of December in Boise, the chance of a day with only rain decreases from 22% to 16%, the chance of a day with mixed snow and rain remains an essentially constant 4% throughout, and the chance of a day with only snow increases from 2% to 5%.
Probability of Precipitation in December in Boise
To show variation within the month and not just the monthly total, we show the rainfall accumulated over a sliding 31-day period centered around each day.
The average sliding 31-day rainfall during December in Boise is essentially constant, remaining about 1.5 inches throughout, and rarely exceeding 3.0 inches or falling below 0.2 inches.
The highest average 31-day accumulation is 1.5 inches on December 7.
Average Monthly Rainfall in December in Boise
As with rainfall, we consider the snowfall accumulated over a sliding 31-day period centered around each day.
The average sliding 31-day snowfall during December in Boise is increasing, starting the month at 2.0 inches, when it rarely exceeds 6.3 inches or falls below -0.0 inches, and ending the month at 3.3 inches, when it rarely exceeds 8.9 inches or falls below 0.1 inches.
The highest average 31-day accumulation is 3.4 inches on December 28.
Average Monthly Snowfall in December in Boise
Over the course of December in Boise, the length of the day is essentially constant. The shortest day of the month is December 21, with 8 hours, 56 minutes of daylight and the longest day is December 1, with 9 hours, 11 minutes of daylight.
Hours of Daylight and Twilight in December in Boise
The earliest sunrise of the month in Boise is 7:58 AM on December 1 and the latest sunrise is 20 minutes later at 8:18 AM on December 31.
The earliest sunset is 5:07 PM on December 9 and the latest sunset is 10 minutes later at 5:17 PM on December 31.
Daylight saving time is observed in Boise during 2023, but it neither starts nor ends during December, so the entire month is in standard time.
For reference, on June 21, the longest day of the year, the Sun rises at 6:03 AM and sets 15 hours, 26 minutes later, at 9:29 PM, while on December 22, the shortest day of the year, it rises at 8:15 AM and sets 8 hours, 56 minutes later, at 5:11 PM.
Sunrise & Sunset with Twilight and Daylight Saving Time in December in Boise
The figure below presents a compact representation of the sun's elevation (the angle of the sun above the horizon) and azimuth (its compass bearing) for every hour of every day in the reporting period. The horizontal axis is the day of the year and the vertical axis is the hour of the day. For a given day and hour of that day, the background color indicates the azimuth of the sun at that moment. The black isolines are contours of constant solar elevation.
Solar Elevation and Azimuth in December in Boise
The figure below presents a compact representation of key lunar data for December 2023. The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases. The label associated with each bar indicates the date and time that the phase is obtained, and the companion time labels indicate the rise and set times of the Moon for the nearest time interval in which the moon is above the horizon.
Moon Rise, Set & Phases in December in Boise
We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.
The chance that a given day will be muggy in Boise is essentially constant during December, remaining around 0% throughout.
For reference, on August 24, the muggiest day of the year, there are muggy conditions 0% of the time, while on January 1, the least muggy day of the year, there are muggy conditions 0% of the time.
Humidity Comfort Levels in December in Boise
dry 55°F comfortable 60°F humid 65°F muggy 70°F oppressive 75°F miserable
This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.
The average hourly wind speed in Boise is essentially constant during December, remaining within 0.2 miles per hour of 6.8 miles per hour throughout.
For reference, on April 1, the windiest day of the year, the daily average wind speed is 7.5 miles per hour, while on September 15, the calmest day of the year, the daily average wind speed is 6.3 miles per hour.
Average Wind Speed in December in Boise
The hourly average wind direction in Boise throughout December is predominantly from the east, with a peak proportion of 37% on December 30.
Wind Direction in December in Boise
Definitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere).
The growing season in Boise typically lasts for 5.9 months (179 days), from around April 23 to around October 19, rarely starting before March 31 or after May 16, and rarely ending before September 26 or after November 10.
The month of December in Boise is reliably fully outside of the growing season.
Time Spent in Various Temperature Bands and the Growing Season in December in Boise
frigid 15°F freezing 32°F very cold 45°F cold 55°F cool 65°F comfortable 75°F warm 85°F hot 95°F sweltering
Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F.
The average accumulated growing degree days in Boise are essentially constant during December, remaining within 1°F of 3,214°F throughout.
Growing Degree Days in December in Boise
This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.
The average daily incident shortwave solar energy in Boise is essentially constant during December, remaining within 0.1 kWh of 1.7 kWh throughout.
The lowest average daily incident shortwave solar energy during December is 1.6 kWh on December 22.
Average Daily Incident Shortwave Solar Energy in December in Boise
For the purposes of this report, the geographical coordinates of Boise are 43.613 deg latitude, -116.203 deg longitude, and 2,697 ft elevation.
The topography within 2 miles of Boise contains significant variations in elevation, with a maximum elevation change of 505 feet and an average elevation above sea level of 2,746 feet. Within 10 miles contains significant variations in elevation (3,980 feet). Within 50 miles also contains extreme variations in elevation (7,556 feet).
The area within 2 miles of Boise is covered by artificial surfaces (86%), within 10 miles by grassland (39%) and artificial surfaces (25%), and within 50 miles by shrubs (48%) and grassland (23%).
This report illustrates the typical weather in Boise, based on a statistical analysis of historical hourly weather reports and model reconstructions from January 1, 1980 to December 31, 2016.
Temperature and Dew Point
There are 3 weather stations near enough to contribute to our estimation of the temperature and dew point in Boise.
For each station, the records are corrected for the elevation difference between that station and Boise according to the International Standard Atmosphere , and by the relative change present in the MERRA-2 satellite-era reanalysis between the two locations.
The estimated value at Boise is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Boise and a given station.
The stations contributing to this reconstruction are:
To get a sense of how much these sources agree with each other, you can view a comparison of Boise and the stations that contribute to our estimates of its temperature history and climate. Please note that each source's contribution is adjusted for elevation and the relative change present in the MERRA-2 data.
All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Algorithms 2nd Edition , by Jean Meeus.
All other weather data, including cloud cover, precipitation, wind speed and direction, and solar flux, come from NASA's MERRA-2 Modern-Era Retrospective Analysis . This reanalysis combines a variety of wide-area measurements in a state-of-the-art global meteorological model to reconstruct the hourly history of weather throughout the world on a 50-kilometer grid.
Land Use data comes from the Global Land Cover SHARE database , published by the Food and Agriculture Organization of the United Nations.
Elevation data comes from the Shuttle Radar Topography Mission (SRTM) , published by NASA's Jet Propulsion Laboratory.
Names, locations, and time zones of places and some airports come from the GeoNames Geographical Database .
Time zones for airports and weather stations are provided by AskGeo.com .
Maps are © OpenStreetMap contributors.
The information on this site is provided as is, without any assurances as to its accuracy or suitability for any purpose. Weather data is prone to errors, outages, and other defects. We assume no responsibility for any decisions made on the basis of the content presented on this site.
We draw particular cautious attention to our reliance on the MERRA-2 model-based reconstructions for a number of important data series. While having the tremendous advantages of temporal and spatial completeness, these reconstructions: (1) are based on computer models that may have model-based errors, (2) are coarsely sampled on a 50 km grid and are therefore unable to reconstruct the local variations of many microclimates, and (3) have particular difficulty with the weather in some coastal areas, especially small islands.
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