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December Weather in Alton, United States

Last updated: June 24, 2025

In Alton, United States, the average temperature in December hovers around 3°C (38°F). Conditions can vary significantly, with minimums plummeting to -19°C (-1°F) and maximums peaking at 21°C (69°F). Expect some moisture, as the area sees 54 mm (2.1 in) of precipitation over an average of 7 days, and prepare for high humidity, averaging around 86%.

December Temperature in Alton

In December in Alton, the average temperature is 3°C (38°F), with maximums reaching 21°C (69°F) and minimums dropping as low as -19°C (-1°F). This range makes Alton a destination for travelers seeking a unique blend of crisp winter air and occasional milder days.

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

The chart illustrates December temperature patterns in Alton, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Alton, December typically has an average temperature of 3°C (38°F), with highs reaching up to 21°C (69°F) and lows dropping to around -19°C (-1°F).
JanFebMarAprMayJunJulAugSepOctNovDec313446546776797672584338
Data source: Temperature data for Alton 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 Alton

In Alton in December, the precipitation amount is 54 mm (2.1 in) over a duration of 7 days.

December Precipitation Trends in Alton

The chart displays monthly precipitation patterns in Alton, 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 Alton, December typically receives around 54 mm (2.1 inches) of precipitation spread over approximately 7 days.
JanFebMarAprMayJunJulAugSepOctNovDec737813212315010196119671007054
Data source: Precipitation data for December generated using information from the Copernicus Climate Change Service.
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December Humidity in Alton

In Alton in December humidity is 86%. With an average temperature of 3°C (38°F), this humidity feels like a damp chill that seeps through your layers, making traveling uncomfortable as breath clouds visibly in the crisp air.

December Average Humidity in Alton

This chart illustrates the average monthly humidity levels in Alton, 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 Alton 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 Alton

In Alton 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 Alton, you can check the information here.

Maximum UV Index Levels in Alton for December

The chart shows the monthly maximum UV Index (UVI) for Alton 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 Alton typically reaches 3, which falls under the moderate exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec356910111199643
Data source: Alton 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 Alton Compares to Other Months

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

This table compares monthly weather conditions in Alton, showing how December’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather0°C (32°F)73 mm (2.9 inches)82%moderate
February Weather1°C (35°F)78 mm (3.1 inches)80%moderate
March Weather8°C (46°F)132 mm (5.2 inches)80%high
April Weather12°C (55°F)123 mm (4.9 inches)80%very high
May Weather19°C (67°F)150 mm (5.9 inches)82%very high
June Weather25°C (77°F)101 mm (4.0 inches)83%extreme
July Weather26°C (79°F)96 mm (3.8 inches)81%extreme
August Weather24°C (76°F)119 mm (4.7 inches)80%very high
September Weather22°C (72°F)67 mm (2.6 inches)76%very high
October Weather15°C (59°F)100 mm (3.9 inches)76%high
November Weather6°C (44°F)70 mm (2.8 inches)85%moderate
December Weather3°C (38°F)54 mm (2.1 inches)86%moderate

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