December Weather in San Antonio United States

Daily high temperatures decrease by 5°F, from 68°F to 63°F, rarely falling below 48°F or exceeding 79°F.

Daily low temperatures decrease by 5°F, from 49°F to 43°F, rarely falling below 31°F or exceeding 64°F.

For reference, on August 5, the hottest day of the year, temperatures in San Antonio typically range from 76°F to 96°F, while on January 6, the coldest day of the year, they range from 43°F to 63°F.

The figure below shows you a compact characterization of the hourly average temperatures for the quarter of the year centered on December. The horizontal axis is the day, the vertical axis is the hour of the day, and the color is the average temperature for that hour and day.

Ben Gardane, Tunisia (6,136 miles away); Ismailia, Egypt (7,183 miles); and Riāsi, India (8,105 miles) are the far-away foreign places with temperatures most similar to San Antonio (view comparison).

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The month of December in San Antonio experiences gradually increasing cloud cover, with the percentage of time that the sky is overcast or mostly cloudy increasing from 38% to 46%.

The clearest day of the month is December 2, with clear, mostly clear, or partly cloudy conditions 62% of the time.

For reference, on January 3, the cloudiest day of the year, the chance of overcast or mostly cloudy conditions is 46%, while on June 10, the clearest day of the year, the chance of clear, mostly clear, or partly cloudy skies is 73%.

A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In San Antonio, the chance of a wet day over the course of December is essentially constant, remaining around 14% throughout.

For reference, the year's highest daily chance of a wet day is 31% on May 26, and its lowest chance is 13% on December 15.

Rainfall

To show variation within the month and not just the monthly total, we show the rainfall accumulated over a sliding 31-day period centered around each day.

The average sliding 31-day rainfall during December in San Antonio is essentially constant, remaining about 1.6 inches throughout, and rarely exceeding 4.1 inches or falling below 0.1 inches.

Over the course of December in San Antonio, the length of the day is essentially constant. The shortest day of the month is December 20, with 10 hours, 16 minutes of daylight and the longest day is December 1, with 10 hours, 23 minutes of daylight.

The earliest sunrise of the month in San Antonio is 7:11 AM on December 1 and the latest sunrise is 17 minutes later at 7:28 AM on December 31.

The earliest sunset is 5:34 PM on December 1 and the latest sunset is 11 minutes later at 5:46 PM on December 31.

Daylight saving time is observed in San Antonio during 2024, but it neither starts nor ends during December, so the entire month is in daylight saving time.

For reference, on June 20, the longest day of the year, the Sun rises at 6:34 AM and sets 14 hours, 2 minutes later, at 8:36 PM, while on December 21, the shortest day of the year, it rises at 7:24 AM and sets 10 hours, 16 minutes later, at 5:40 PM.

The figure below presents a compact representation of the sun's elevation (the angle of the sun above the horizon) and azimuth (its compass bearing) for every hour of every day in the reporting period. The horizontal axis is the day of the year and the vertical axis is the hour of the day. For a given day and hour of that day, the background color indicates the azimuth of the sun at that moment. The black isolines are contours of constant solar elevation.

The figure below presents a compact representation of key lunar data for December 2024. The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases. The label associated with each bar indicates the date and time that the phase is obtained, and the companion time labels indicate the rise and set times of the Moon for the nearest time interval in which the moon is above the horizon.

We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid. Unlike temperature, which typically varies significantly between night and day, dew point tends to change more slowly, so while the temperature may drop at night, a muggy day is typically followed by a muggy night.

The chance that a given day will be muggy in San Antonio is decreasing during December, falling from 8% to 3% over the course of the month.

For reference, on June 30, the muggiest day of the year, there are muggy conditions 89% of the time, while on January 23, the least muggy day of the year, there are muggy conditions 2% of the time.

This section discusses the wide-area hourly average wind vector (speed and direction) at 10 meters above the ground. The wind experienced at any given location is highly dependent on local topography and other factors, and instantaneous wind speed and direction vary more widely than hourly averages.

The average hourly wind speed in San Antonio is essentially constant during December, remaining within 0.1 miles per hour of 9.2 miles per hour throughout.

For reference, on April 1, the windiest day of the year, the daily average wind speed is 10.4 miles per hour, while on September 4, the calmest day of the year, the daily average wind speed is 7.9 miles per hour.

The wind direction in San Antonio during December is predominantly out of the south from December 1 to December 8 and the north from December 8 to December 31.

Definitions of the growing season vary throughout the world, but for the purposes of this report, we define it as the longest continuous period of non-freezing temperatures (≥ 32°F) in the year (the calendar year in the Northern Hemisphere, or from July 1 until June 30 in the Southern Hemisphere).

The growing season in San Antonio typically lasts for 9.8 months (299 days), from around February 15 to around December 9, rarely starting after March 11, or ending before November 17.

During December in San Antonio, the chance that a given day is within the growing season is very rapidly decreasing falling from 69% to 14% over the course of the month.

Growing degree days are a measure of yearly heat accumulation used to predict plant and animal development, and defined as the integral of warmth above a base temperature, discarding any excess above a maximum temperature. In this report, we use a base of 50°F and a cap of 86°F.

The average accumulated growing degree days in San Antonio are increasing during December, increasing by 216°F, from 7,045°F to 7,261°F, over the course of the month.

This section discusses the total daily incident shortwave solar energy reaching the surface of the ground over a wide area, taking full account of seasonal variations in the length of the day, the elevation of the Sun above the horizon, and absorption by clouds and other atmospheric constituents. Shortwave radiation includes visible light and ultraviolet radiation.

The average daily incident shortwave solar energy in San Antonio is essentially constant during December, remaining within 0.1 kWh of 3.3 kWh throughout.

The lowest average daily incident shortwave solar energy during December is 3.2 kWh on December 18.

For the purposes of this report, the geographical coordinates of San Antonio are 29.424 deg latitude, -98.494 deg longitude, and 636 ft elevation.

The topography within 2 miles of San Antonio contains only modest variations in elevation, with a maximum elevation change of 151 feet and an average elevation above sea level of 657 feet. Within 10 miles contains only modest variations in elevation (577 feet). Within 50 miles contains significant variations in elevation (1,831 feet).

The area within 2 miles of San Antonio is covered by artificial surfaces (100%), within 10 miles by artificial surfaces (65%) and shrubs (23%), and within 50 miles by shrubs (38%) and cropland (25%).