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December Weather in San Ysidro, United States

Last updated: June 24, 2025

In December, the average temperature in San Ysidro, United States hovers around 8°C (47°F). Expect a range from a chilly -6°C (22°F) to a warm 23°C (73°F) during this month. With an average humidity of 82%, the air can feel quite damp, complemented by 12 mm (0.5 in) of precipitation spread over just 2 days.

December Temperature in San Ysidro

In December in San Ysidro, the average temperature is 8°C (47°F). Maximums can reach 23°C (73°F) and minimums can be as low as -6°C (22°F). Be prepared for a wide range of temperatures while traveling, so layer your clothing accordingly.

December Weather in San Ysidro: Daily Temperature Highs, Lows, and Averages

The chart illustrates December temperature patterns in San Ysidro, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In San Ysidro, December typically has an average temperature of 8°C (47°F), with highs reaching up to 23°C (73°F) and lows dropping to around -6°C (22°F).
JanFebMarAprMayJunJulAugSepOctNovDec455058677583838277665546
Data source: Temperature data for San Ysidro 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.

December Precipitation in San Ysidro

In San Ysidro in December, the precipitation amount is 12 mm (0.5 in) over the course of 2 days.

December Precipitation Trends in San Ysidro

The chart displays monthly precipitation patterns in San Ysidro, with values for each month alongside December’s data, which is highlighted for easy comparison. It shows the amount of precipitation, providing insights into how December’s conditions compare to those of other months. In San Ysidro, December typically receives around 12 mm (0.5 inches) of precipitation spread over approximately 2 days.
JanFebMarAprMayJunJulAugSepOctNovDec1315163422313324211313
Data source: Precipitation data for December generated using information from the Copernicus Climate Change Service.
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December Humidity in San Ysidro

In San Ysidro in December humidity is 82%. With an average temperature of 8°C (47°F), this humidity feels like a damp chill that seeps into your bones, making outdoor exploration less enjoyable and requiring extra layers to stay warm and comfortable.

December Average Humidity in San Ysidro

This chart illustrates the average monthly humidity levels in San Ysidro, with December’s data highlighted for easy comparison. It shows the fluctuation in humidity throughout the year, helping you understand how conditions vary by season. In December, average humidity in San Ysidro is approximately 82%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec79%79%65%55%54%53%55%58%70%75%83%82%
Data source: Humidity data for December generated using information from the Copernicus Climate Change Service.

December UV Index in San Ysidro

In San Ysidro in December, the maximum UV index reaches 5, which corresponds to a moderate Exposure Category. Under these conditions, the estimated time to burn is approximately 30 minutes. For more details, you can check the Hourly UV Index in San Ysidro.

Maximum UV Index Levels in San Ysidro for December

The chart shows the monthly maximum UV Index (UVI) for San Ysidro in December, 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 December, the maximum UV index in San Ysidro typically reaches 5, which falls under the moderate exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec5710121213121211865
Data source: San Ysidro December 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 December Weather in San Ysidro Compares to Other Months

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

This table compares monthly weather conditions in San Ysidro, showing how December’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather7°C (45°F)13 mm (0.5 inches)79%moderate
February Weather10°C (50°F)14 mm (0.6 inches)79%high
March Weather14°C (58°F)16 mm (0.6 inches)65%very high
April Weather20°C (67°F)3 mm (0.1 inches)55%extreme
May Weather24°C (75°F)4 mm (0.2 inches)54%extreme
June Weather28°C (84°F)22 mm (0.9 inches)53%extreme
July Weather29°C (84°F)31 mm (1.2 inches)55%extreme
August Weather28°C (83°F)33 mm (1.3 inches)57%extreme
September Weather25°C (77°F)24 mm (0.9 inches)70%extreme
October Weather19°C (66°F)21 mm (0.8 inches)75%very high
November Weather13°C (56°F)13 mm (0.5 inches)83%high
December Weather8°C (47°F)12 mm (0.5 inches)82%moderate

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