This report describes the typical weather at the Phoenix Deer Valley Airport (Phoenix, Arizona, United States) weather station over the course of an average December. It is based on the historical records from 1997 to 2012. Earlier records are either unavailable or unreliable.
Phoenix, Arizona has a hot desert climate. The area within 25 mi of this station is covered by shrublands (86%), grasslands (8%), built-up areas (3%), and croplands (2%).
The month of December is characterized by gradually falling daily high temperatures, with daily highs ranging from 66°F to 63°F over the course of the month, exceeding 74°F or dropping below 55°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 22 with 9:55 hours of daylight; the longest day is December 1 with 10:05 hours of daylight.
The earliest sunrise is at 7:15am on December 1; the latest sunset is at 5:31pm on December 31; the latest sunrise is at 7:33am on December 30; the earliest sunset is at 5:19pm on December 6.
Daylight savings time (DST) is not observed in 2012.
The median cloud cover is 0% (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 81% of the time, partly cloudy 3% of the time, and mostly cloudy or overcast 13% of the time.
The average probability that some form of precipitation will be observed in a given day is 14%, with little variation over the course of the month.
Throughout December, the most common forms of precipitation are light rain, moderate rain, and thunderstorms.
Light rain is the most severe precipitation observed during 57% of those days with precipitation. It is most likely around December 27, when it is observed during 9% of all days.
Moderate rain is the most severe precipitation observed during 21% of those days with precipitation. It is most likely around December 26, when it is observed during 3% of all days.
Thunderstorms are the most severe precipitation observed during 11% of those days with precipitation. They are most likely around December 5, when it is observed during 2% of all days.
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 24% (dry) to 63% (mildly humid) over the course of a typical December, rarely dropping below 11% (very dry), or exceeding 91% (very humid).
The air is driest around December 1, at which time the relative humidity drops below 29% (dry) three days out of four; it is most humid around December 21, rising above 48% (comfortable) 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 23°F (dry) to 34°F (dry) and is rarely below 7°F (dry) or above 47°F (dry).
Over the course of December typical wind speeds vary from 0 mph to 11 mph (calm to gentle breeze), rarely exceeding 18 mph (fresh breeze).
The highest average wind speed of 5 mph (light breeze) occurs around December 7, at which time the average daily maximum wind speed is 11 mph (gentle breeze).
The lowest average wind speed of 5 mph (light breeze) occurs around December 31, at which time the average daily maximum wind speed is 10 mph (gentle breeze).