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December Weather in O'Fallon, United States

Last updated: June 24, 2025

In December, the average temperature in O'Fallon, United States hovers around 4°C (39°F). During this time, temperatures can dip as low as -17°C (2°F) and soar to a maximum of 22°C (72°F). Expect about 52 mm (2.1 in) of precipitation spread over 7 days, with an average humidity of 86%. Stay prepared for a chilly yet interesting month ahead!

December Temperature in O'Fallon

In December in O'Fallon, the average temperature is 4°C (39°F). Maximum temperatures can reach up to 22°C (72°F), while minimum temperatures can drop as low as -17°C (2°F). Be prepared for a wide range of temperatures to ensure a comfortable and enjoyable travel experience.

December Weather in O'Fallon: Daily Temperature Highs, Lows, and Averages

The chart illustrates December temperature patterns in O'Fallon, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In O'Fallon, December typically has an average temperature of 4°C (39°F), with highs reaching up to 22°C (72°F) and lows dropping to around -17°C (2°F).
JanFebMarAprMayJunJulAugSepOctNovDec323546556776797672594439
Data source: Temperature data for O'Fallon 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 O'Fallon

In O'Fallon in December, the precipitation amount is 52 mm (2.1 in) over the course of 7 days.

December Precipitation Trends in O'Fallon

The chart displays monthly precipitation patterns in O'Fallon, 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 O'Fallon, December typically receives around 52 mm (2.1 inches) of precipitation spread over approximately 7 days.
JanFebMarAprMayJunJulAugSepOctNovDec72781281211458497139561106852
Data source: Precipitation data for December generated using information from the Copernicus Climate Change Service.
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December Humidity in O'Fallon

In O'Fallon in December humidity is 86%. With an average temperature of 4°C (39°F), this humidity feels like a chilly mist enveloping you, making it essential to bundle up while exploring, as each breath comes with a damp chill that can be quite refreshing yet starkly invigorating for travelers.

December Average Humidity in O'Fallon

This chart illustrates the average monthly humidity levels in O'Fallon, 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 O'Fallon is approximately 86%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec82%80%80%80%82%83%81%80%76%76%85%86%
Data source: Humidity data for December generated using information from the Copernicus Climate Change Service.

December UV Index in O'Fallon

In O'Fallon in December, the maximum UV index is 3, which corresponds to a moderate Exposure Category. The time to burn is approximately 30 minutes. For more details on the hourly UV index in O'Fallon, you can check the information here.

Maximum UV Index Levels in O'Fallon for December

The chart shows the monthly maximum UV Index (UVI) for O'Fallon 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 O'Fallon typically reaches 3, which falls under the moderate exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec3569101111109653
Data source: O'Fallon 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 O'Fallon Compares to Other Months

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

This table compares monthly weather conditions in O'Fallon, showing how December’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather0°C (32°F)72 mm (2.9 inches)82%moderate
February Weather2°C (35°F)78 mm (3.1 inches)80%moderate
March Weather8°C (47°F)128 mm (5.0 inches)80%high
April Weather13°C (55°F)121 mm (4.8 inches)80%very high
May Weather19°C (67°F)145 mm (5.7 inches)82%very high
June Weather25°C (76°F)84 mm (3.3 inches)83%extreme
July Weather26°C (80°F)97 mm (3.8 inches)81%extreme
August Weather24°C (76°F)139 mm (5.5 inches)80%very high
September Weather22°C (72°F)56 mm (2.2 inches)76%very high
October Weather15°C (59°F)110 mm (4.3 inches)76%high
November Weather7°C (44°F)68 mm (2.7 inches)85%moderate
December Weather4°C (39°F)52 mm (2.1 inches)86%moderate

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