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%).
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.
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.
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.
The median cloud cover is 13% (mostly clear) and does not vary substantially over the course of the month.
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.
There is either very little precipitation at this location in December, or the weather station does not reliably report the conditions.
Either snow is exceptionally unlikely to fall at this location in December or this station does not reliably report precipitation types.
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.
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).
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).