This report describes the typical weather at the San Antonio International Airport (San Antonio, Texas, United States) weather station over the course of an average December. It is based on the historical records from 1974 to 2012. Earlier records are either unavailable or unreliable.
San Antonio, Texas has a warm humid temperate climate with hot summers and no dry season. The area within 25 mi of this station is covered by grasslands (56%), forests (20%), croplands (14%), and built-up areas (9%).
The month of December is characterized by falling daily high temperatures, with daily highs decreasing from 67°F to 61°F over the course of the month, exceeding 78°F or dropping below 46°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 21 with 10:15 hours of daylight; the longest day is December 1 with 10:23 hours of daylight.
The earliest sunrise is at 7:12am on December 1; the latest sunset is at 5:46pm on December 31; the latest sunrise is at 7:29am on December 30; the earliest sunset is at 5:34pm on December 2.
Daylight savings time is observed in 2012 but it neither starts nor ends in December, so the entire month is in standard time.
The median cloud cover ranges from 73% (partly cloudy) to 78% (partly cloudy). The trend is for the sky to be becoming cloudier with the median cloud cover increasing by 6% from the start to the end of the month.
On December 16, a representative day, the sky is clear or mostly clear 37% of the time, partly cloudy 11% of the time, and mostly cloudy or overcast 51% of the time.
The average probability that some form of precipitation will be observed in a given day is 38%, with little variation over the course of the month.
Throughout December, the most common forms of precipitation are light rain, moderate rain, and drizzle.
Light rain is the most severe precipitation observed during 39% of those days with precipitation. It is most likely around December 29, when it is observed during 16% of all days.
Moderate rain is the most severe precipitation observed during 25% of those days with precipitation. It is most likely around December 31, when it is observed during 10% of all days.
Drizzle is the most severe precipitation observed during 22% of those days with precipitation. It is most likely around December 23, when it is observed during 9% 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 44% (comfortable) to 89% (very humid) over the course of a typical December, rarely dropping below 20% (dry) and reaching as high as 100% (very humid).
The air is driest around December 7, at which time the relative humidity drops below 58% (mildly humid) three days out of four; it is most humid around December 3, rising above 85% (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 31°F (dry) to 50°F (very comfortable) and is rarely below 16°F (dry) or above 67°F (muggy).
Over the course of December typical wind speeds vary from 0 mph to 14 mph (calm to moderate breeze), rarely exceeding 21 mph (fresh breeze).
The highest average wind speed of 8 mph (gentle breeze) occurs around December 1, at which time the average daily maximum wind speed is 14 mph (moderate breeze).
The lowest average wind speed of 8 mph (gentle breeze) occurs around December 9, at which time the average daily maximum wind speed is 14 mph (moderate breeze).