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January Weather in San Marcos, United States

Last updated: June 24, 2025

In January, the average temperature in San Marcos, United States hovers around 13°C (56°F), with a potential range from a chilly 4°C (40°F) to a warm 30°C (87°F). Expect about 70 mm (2.8 in) of precipitation over approximately 5 days, contributing to an overall average humidity of 72%. Whether you're basking in the sun or seeking shelter from the rain, be prepared for the dynamic climate!

January Temperature in San Marcos

In January in San Marcos, the average temperature is 13°C (56°F). Maximums can reach 30°C (87°F) and minimums can be as low as 4°C (40°F). This climate makes it essential to pack layers for your travels, ensuring comfort throughout varying weather conditions.

January Weather in San Marcos: Daily Temperature Highs, Lows, and Averages

The chart illustrates January temperature patterns in San Marcos, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In San Marcos, January typically has an average temperature of 13°C (56°F), with highs reaching up to 30°C (87°F) and lows dropping to around 4°C (40°F).
JanFebMarAprMayJunJulAugSepOctNovDec565657616368737573686356
Data source: Temperature data for San Marcos generated using information from the Copernicus Climate Change Service.
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The average of daily temperatures (24 hours) calculated across all days in the month.

January Precipitation in San Marcos

In San Marcos in January, the precipitation amount is 70 mm (2.8 in) over the course of 5 days.

January Precipitation Trends in San Marcos

The chart displays monthly precipitation patterns in San Marcos, with values for each month alongside January’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how January’s conditions compare to those of other months. In San Marcos, January typically receives around 70 mm (2.8 inches) of precipitation spread over approximately 5 days.
JanFebMarAprMayJunJulAugSepOctNovDec70786832243415123570
Data source: Precipitation data for January generated using information from the Copernicus Climate Change Service.
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January Humidity in San Marcos

In San Marcos in January, humidity is 72%. With an average temperature of 13°C (56°F), this humidity feels like a damp blanket enveloping you, making outdoor activities somewhat uncomfortable and reminding travelers to stay hydrated and seek shade whenever possible.

January Average Humidity in San Marcos

This chart illustrates the average monthly humidity levels in San Marcos, with January’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In January, average humidity in San Marcos is approximately 72%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec72%77%67%56%46%48%46%42%52%58%66%74%
Data source: Humidity data for January generated using information from the Copernicus Climate Change Service.

January UV Index in San Marcos

In San Marcos in January, the maximum UV index reaches 4, which corresponds to a moderate Exposure Category. With a time to burn of 30 minutes, it’s important to take precautions to protect your skin. You can find more details in the Hourly UV Index in San Marcos for better planning.

Maximum UV Index Levels in San Marcos for January

The chart shows the monthly maximum UV Index (UVI) for San Marcos in January, representing the highest UV radiation level. The UVI measures the intensity of ultraviolet radiation from the sun, indicating the potential risk of sunburn and UV-related health issues. In January, the maximum UV index in San Marcos typically reaches 4, which falls under the moderate exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec469101112111010754
Data source: San Marcos January UVI data generated using information from the Copernicus Climate Change Service.

UV Risk Categories

  •  Extreme (11+): Avoid the sun, stay in shade.
  •  Very High (8-10): Limit sun exposure.
  •  High (6-7): Use SPF 30+ and protective clothing.
  •  Moderate (3-5): Midday shade recommended.
  •  Low (0-2): No protection needed.

How January Weather in San Marcos Compares to Other Months

Weather in San Marcos varies notably across the year, with each month offering distinct climate conditions. This page compares January’s weather to other months in San Marcos, focusing on differences in temperature, rainfall, humidity, and UV levels.

This table compares monthly weather conditions in San Marcos, showing how January’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather13°C (56°F)70 mm (2.8 inches)72%moderate
February Weather13°C (56°F)78 mm (3.1 inches)77%high
March Weather14°C (58°F)68 mm (2.7 inches)67%very high
April Weather16°C (62°F)32 mm (1.3 inches)56%very high
May Weather17°C (63°F)24 mm (0.9 inches)46%extreme
June Weather20°C (68°F)3 mm (0.1 inches)48%extreme
July Weather23°C (73°F)4 mm (0.2 inches)46%extreme
August Weather24°C (75°F)1 mm (0.1 inches)42%very high
September Weather23°C (73°F)5 mm (0.2 inches)52%very high
October Weather20°C (69°F)12 mm (0.5 inches)58%high
November Weather17°C (63°F)34 mm (1.4 inches)66%moderate
December Weather14°C (57°F)70 mm (2.7 inches)74%moderate

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