Average Weather in December in Boulder Colorado, United States
In Boulder, the month of December is characterized by gradually falling daily high temperatures, with daily highs decreasing by 4°F, from 47°F to 42°F over the course of the month, and rarely exceeding 63°F or dropping below 26°F. The lowest daily average high temperature is 42°F on December 30.
Daily low temperatures decrease by 4°F, from 26°F to 22°F, rarely falling below 6°F or exceeding 38°F. The lowest daily average low temperature is 22°F on December 30.
For reference, on July 10, the hottest day of the year, temperatures in Boulder typically range from 60°F to 87°F, while on December 30, the coldest day of the year, they range from 22°F to 42°F.
Average High and Low Temperature in December
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
The month of December in Boulder experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 41% throughout the month.
The clearest day of the month is December 26, with clear, mostly clear, or partly cloudy conditions 60% of the time.
For reference, on May 5, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 48%, while on September 13, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 74%.
Cloud Cover in December
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In Boulder, the chance of a wet day over the course of December is essentially constant, remaining around 9% throughout.
For reference, the year's highest daily chance of a wet day is 29% on July 22, and its lowest chance is 8% on January 11.
Over the course of December in Boulder, the chance of a day with only rain remains an essentially constant 3% throughout, the chance of a day with mixed snow and rain remains an essentially constant 2% throughout, and the chance of a day with only snow remains an essentially constant 4% throughout.
Probability of Precipitation in December
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 Boulder is essentially constant, remaining about 0.2 inches throughout, and rarely exceeding 0.5 inches.
The lowest average 31-day accumulation is 0.1 inches on December 27.
Average Monthly Rainfall in December
We report snowfall in liquid-equivalent terms. The actual depth of new snowfall is typically between 5 and 10 times the liquid-equivalent amount, assuming the ground is frozen. As with rainfall, we consider the liquid-equivalent snowfall accumulated over a sliding 31-day period centered around each day.
The average sliding 31-day liquid-equivalent snowfall during December in Boulder is essentially constant, remaining about 0.3 inches throughout, and rarely exceeding 0.7 inches or falling to 0.0 inches.
The highest average 31-day liquid-equivalent accumulation is 0.3 inches on December 21.
Average Monthly Liquid-Equivalent Snowfall in December
Over the course of December in Boulder, the length of the day is essentially constant. The shortest day of the month is December 21, with 9 hours, 20 minutes of daylight and the longest day is December 1, with 9 hours, 32 minutes of daylight.
Hours of Daylight and Twilight in December
The earliest sunrise of the month in Boulder is 7:04 AM on December 1 and the latest sunrise is 19 minutes later at 7:22 AM on December 31.
The earliest sunset is 4:35 PM on December 7 and the latest sunset is 10 minutes later at 4:45 PM on December 31.
Daylight saving time is observed in Boulder during 2017, 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 5:32 AM and sets 15 hours, 1 minute later, at 8:33 PM, while on December 21, the shortest day of the year, it rises at 7:19 AM and sets 9 hours, 20 minutes later, at 4:39 PM.
Sunrise & Sunset with Twilight and Daylight Saving Time in December
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 Boulder is essentially constant during December, remaining around 0% throughout.
For reference, on July 21, the muggiest day of the year, there are muggy conditions 0% of the time, while on January 1, the leasy muggy day of the year, there are muggy conditions 0% of the time.
Humidity Comfort Levels in December
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 Boulder is essentially constant during December, remaining within 0.2 miles per hour of 5.0 miles per hour throughout.
For reference, on January 16, the windiest day of the year, the daily average wind speed is 5.5 miles per hour, while on August 19, the calmest day of the year, the daily average wind speed is 3.1 miles per hour.
Average Wind Speed in December
Wind Direction in December
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 Boulder is essentially constant during December, remaining within 0.1 kWh of 2.5 kWh throughout.
The lowest average daily incident shortwave solar energy during December is 2.4 kWh on December 22.
Average Daily Incident Shortwave Solar Energy in December
For the purposes of this report, the geographical coordinates of Boulder are 40.015 deg latitude, -105.271 deg longitude, and 5,430 ft elevation.
The topography within 2 miles of Boulder contains very significant variations in elevation, with a maximum elevation change of 1,627 feet and an average elevation above sea level of 5,464 feet. Within 10 miles contains very significant variations in elevation (4,131 feet). Within 50 miles also contains extreme variations in elevation (9,718 feet).
The area within 2 miles of Boulder is covered by artificial surfaces (70%) and shrubs (25%), within 10 miles by trees (33%) and shrubs (25%), and within 50 miles by trees (39%) and grassland (19%).
This report illustrates the typical weather in Boulder year round, 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 Boulder.
For each station, the records are corrected for the elevation difference between that station and Boulder 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 Boulder is computed as the weighted average of the individual contributions from each station, with weights proportional to the inverse of the distance between Boulder and a given station.
The stations contributing to this reconstruction are: Boulder Municipal Airport (98%, 5.0 kilometers, northeast), Kremmling, Mc Elroy Airfield (1.4%, 94 kilometers, west), and Copper Mountain, Red Cliff Pass (0.5%, 97 kilometers, southwest).
All data relating to the Sun's position (e.g., sunrise and sunset) are computed using astronomical formulas from the book, Astronomical Tables of the Sun, Moon and Planets , 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 aiports and weather stations are provided by AskGeo.com .
Maps are © Esri, with data from National Geographic, Esri, DeLorme, NAVTEQ, UNEP-WCMC, USGS, NASA, ESA, METI, NRCAN, GEBCO, NOAA, and iPC.