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December Weather in Ontario, United States

Last updated: June 24, 2025

In December, the average temperature in Ontario, United States hovers around 1°C (35°F), with extremes ranging from a chilling -19°C (-1°F) to a mild 17°C (63°F). Expect around 92 mm (3.6 in) of precipitation spread over 12 days, contributing to an average humidity of 86%.

December Temperature in Ontario

In December in Ontario, the average temperature is 1°C (35°F), with maximums reaching 17°C (63°F) and minimums plummeting to as low as -19°C (-1°F). Travelers should be prepared for a significant range in temperatures and pack accordingly for both chilly and mild conditions.

December Weather in Ontario: Daily Temperature Highs, Lows, and Averages

The chart illustrates December temperature patterns in Ontario, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Ontario, December typically has an average temperature of 1°C (35°F), with highs reaching up to 17°C (63°F) and lows dropping to around -19°C (-1°F).
JanFebMarAprMayJunJulAugSepOctNovDec293240506270747267564135
Data source: Temperature data for Ontario 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 Ontario

In Ontario in December, the precipitation amount is 92 mm (3.6 in) over the course of 12 days.

December Precipitation Trends in Ontario

The chart displays monthly precipitation patterns in Ontario, 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 Ontario, December typically receives around 92 mm (3.6 inches) of precipitation spread over approximately 12 days.
JanFebMarAprMayJunJulAugSepOctNovDec81981031301261411238980989292
Data source: Precipitation data for December generated using information from the Copernicus Climate Change Service.
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December Humidity in Ontario

In Ontario in December, humidity is 86%. With an average temperature of 1°C (35°F), this humidity feels like a biting chill that wraps around you, making outdoor exploration uncomfortable and requiring extra layers to stay warm while navigating the damp air.

December Average Humidity in Ontario

This chart illustrates the average monthly humidity levels in Ontario, 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 Ontario is approximately 86%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec88%87%87%88%81%82%81%78%78%82%89%86%
Data source: Humidity data for December generated using information from the Copernicus Climate Change Service.

December UV Index in Ontario

In Ontario in December, the maximum UV index is 2, which corresponds to a low exposure category. With this level of UV radiation, the time to burn is approximately 45 minutes. To learn more about the hourly UV index in Ontario, you can visit Hourly UV Index in Ontario.

Maximum UV Index Levels in Ontario for December

The chart shows the monthly maximum UV Index (UVI) for Ontario 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 Ontario typically reaches 2, which falls under the low exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec356810101098642
Data source: Ontario 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 Ontario Compares to Other Months

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

This table compares monthly weather conditions in Ontario, showing how December’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather-2°C (29°F)81 mm (3.2 inches)88%moderate
February Weather0°C (32°F)98 mm (3.8 inches)87%moderate
March Weather5°C (40°F)103 mm (4.1 inches)87%high
April Weather10°C (50°F)130 mm (5.1 inches)87%very high
May Weather17°C (62°F)126 mm (5.0 inches)81%very high
June Weather21°C (71°F)141 mm (5.5 inches)82%very high
July Weather24°C (75°F)123 mm (4.8 inches)81%very high
August Weather22°C (72°F)89 mm (3.5 inches)78%very high
September Weather20°C (67°F)80 mm (3.2 inches)78%very high
October Weather14°C (57°F)98 mm (3.9 inches)82%high
November Weather5°C (41°F)92 mm (3.6 inches)89%moderate
December Weather1°C (35°F)92 mm (3.6 inches)86%low

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