This report describes the typical weather at the Mathis Field (San Angelo, 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 Angelo, Texas has a hot semi-arid steppe climate. The area within 25 mi of this station is covered by grasslands (98%).
The month of December is characterized by falling daily high temperatures, with daily highs decreasing from 63°F to 57°F over the course of the month, exceeding 76°F or dropping below 41°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 23 with 10:06 hours of daylight; the longest day is December 1 with 10:15 hours of daylight.
The earliest sunrise is at 7:23am on December 1; the latest sunset is at 5:50pm on December 31; the latest sunrise is at 7:41am on December 30; the earliest sunset is at 5:38pm 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 is 17% (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 58% of the time, partly cloudy 9% of the time, and mostly cloudy or overcast 33% of the time.
The average probability that some form of precipitation will be observed in a given day is 21%, with little variation over the course of the month.
Throughout December, the most common forms of precipitation are light rain, moderate rain, drizzle, and thunderstorms.
Light rain is the most severe precipitation observed during 40% of those days with precipitation. It is most likely around December 1, when it is observed during 9% of all days.
Moderate rain is the most severe precipitation observed during 18% of those days with precipitation. It is most likely around December 2, when it is observed during 4% of all days.
Drizzle is the most severe precipitation observed during 11% of those days with precipitation. It is most likely around December 31, 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 1, when it is observed during 3% of all days.
The likelihood of snow falling is highest around December 25, occurring in 5% of days.
Either snow rarely accumulates at this location in December or snow depth measurements are unavailable or unreliable.
The relative humidity typically ranges from 37% (comfortable) to 86% (very humid) over the course of a typical December, rarely dropping below 17% (dry) and reaching as high as 100% (very humid).
The air is driest around December 6, at which time the relative humidity drops below 49% (comfortable) three days out of four; it is most humid around December 13, rising above 78% (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 23°F (dry) to 41°F (dry) and is rarely below 11°F (dry) or above 57°F (comfortable).
Over the course of December typical wind speeds vary from 1 mph to 18 mph (light air to moderate breeze), rarely exceeding 24 mph (strong breeze).
The highest average wind speed of 10 mph (gentle breeze) occurs around December 3, at which time the average daily maximum wind speed is 18 mph (moderate breeze).
The lowest average wind speed of 10 mph (gentle breeze) occurs around December 24, at which time the average daily maximum wind speed is 17 mph (moderate breeze).