Average Weather In December For Boulder, Colorado, USA

Location

This report describes the typical weather at the Boulder Municipal Airport (Boulder, Colorado, United States) weather station over the course of an average December. It is based on the historical records from 2010 to 2013. Earlier records are either unavailable or unreliable.

Boulder, Colorado has a humid continental climate with warm summers and no dry season. The area within 25 mi of this station is covered by grasslands (40%), forests (32%), shrublands (18%), built-up areas (8%), and croplands (3%).

Temperature

The month of December is characterized by falling daily high temperatures, with daily highs ranging from 48°F to 42°F over the course of the month, exceeding 57°F or dropping below 32°F only one day in ten.

Daily High and Low Temperature in December

The daily average low (blue) and high (red) temperature with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).
Daily low temperatures range from 21°F to 27°F, falling below 14°F or exceeding 33°F only one day in ten.

Fraction of Time Spent in Various Temperature Bands in December

The average fraction of time spent in various temperature bands: frigid (below 15°F), freezing (15°F to 32°F), cold (32°F to 50°F), cool (50°F to 65°F), comfortable (65°F to 75°F), warm (75°F to 85°F), hot (85°F to 100°F) and sweltering (above 100°F).

Sun

Over the course of December, the length of the day is essentially constant. The shortest day of the month is December 19 with 9:20 hours of daylight; the longest day is December 1 with 9:32 hours of daylight.

Daily Hours of Daylight and Twilight in December

The number of hours during which the Sun is visible (black line), with various degrees of daylight, twilight, and night, indicated by the color bands. From bottom (most yellow) to top (most gray): full daylight, solar twilight (Sun is visible but less than 6° from the horizon), civil twilight (Sun is not visible but is less than 6° below the horizon), nautical twilight (Sun is between 6° and 12° below the horizon), astronomical twilight (Sun is between 12° and 18° below the horizon), and full night.

The earliest sunrise is at 7:04am on December 1; the latest sunset is at 4:46pm on December 31; the latest sunrise is at 7:23am on December 31; the earliest sunset is at 4:35pm on December 6.

Daylight saving time is observed in 2013 but it neither starts nor ends in December, so the entire month is in standard time.

Daily Sunrise & Sunset with Twilight and Daylight Saving Time in December

The solar day over the course of the year 2013 . From bottom to top, the black lines are the previous solar midnight, sunrise, solar noon, sunset, and the next solar midnight. The day, twilights (solar, civil, nautical, and astronomical), and night are indicated by the color bands from yellow to gray. The transitions to and from daylight saving time are indicated by the "DST" labels.

Clouds

The median cloud cover is 13% (mostly clear) and does not vary substantially over the course of the month.

Median Cloud Cover in December

The median daily cloud cover (black line) with percentile bands (inner band from 40th to 60th percentile, outer band from 25th to 75th percentile).

On December 16, a representative day, the sky is clear or mostly clear 68% of the time, partly cloudy 5% of the time, and mostly cloudy or overcast 15% of the time.

Cloud Cover Types in December

The fraction of time spent in each of the five sky cover categories. From top (most blue) to bottom (most gray), the categories are clear, mostly clear, partly cloudy, mostly cloudy, and overcast. Pink indicates missing data. Outside of the United States clear skies are often reported ambiguously, leading them to be lumped in with the missing data.

Precipitation

There is either very little precipitation at this location in December, or the weather station does not reliably report the conditions.

Snow

Either snow is exceptionally unlikely to fall at this location in December or this station does not reliably report precipitation types.

Humidity

The relative humidity typically ranges from 25% (dry) to 76% (humid) over the course of a typical December, rarely dropping below 16% (dry), or exceeding 88% (very humid).

The air is driest around December 1, at which time the relative humidity drops below 31% (comfortable) three days out of four; it is most humid around December 16, rising above 68% (mildly humid) three days out of four.

Relative Humidity in December

The average daily high (blue) and low (brown) relative humidity with percentile bands (inner bands from 25th to 75th percentile, outer bands from 10th to 90th percentile).

Dew Point

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 typical December, the dew point typically varies from 6°F (dry) to 22°F (dry) and is rarely below -0°F (dry) or above 26°F (dry).

Dew Point in December

The daily average low (blue) and high (red) dew point with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).

Wind

Over the course of December typical wind speeds vary from 0 mph to 12 mph (calm to moderate breeze), rarely exceeding 19 mph (fresh breeze).

The highest average wind speed of 5 mph (light breeze) occurs around December 1, at which time the average daily maximum wind speed is 12 mph (moderate breeze).

The lowest average wind speed of 3 mph (light air) occurs around December 16, at which time the average daily maximum wind speed is 9 mph (gentle breeze).

Wind Speed in December

The average daily minimum (red), maximum (green), and average (black) wind speed with percentile bands (inner band from 25th to 75th percentile, outer band from 10th to 90th percentile).
The wind is most often out of the west (14% of the time), north (12% of the time), and south west (12% of the time).

Wind Directions in December

The fraction of time spent with the wind blowing from the various directions over the entire year. Values do not sum to 100% because the wind direction is undefined when the wind speed is zero.

Fraction of Time Spent with Various Wind Directions in December

The fraction of time spent with the wind blowing from the various directions on a daily basis. Stacked values do not always sum to 100% because the wind direction is undefined when the wind speed is zero.