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December Weather in Longmont, United States

Last updated: June 24, 2025

In December, the average temperature in Longmont, United States hovers around 0°C (33°F), with minimums dipping as low as -16°C (3°F) and maximums reaching up to 22°C (72°F). Expect about 15 mm (0.6 in) of precipitation spread over 3 days, and prepare for a relatively damp environment with an average humidity of 85%.

December Temperature in Longmont

In December in Longmont, the average temperature is 0°C (33°F). Maximums can reach 22°C (72°F) and minimums can be as low as -16°C (3°F). Be prepared for varied weather conditions if you plan to travel during this time, as temperatures can fluctuate significantly.

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

The chart illustrates December temperature patterns in Longmont, showcasing daily minimum, maximum, and average temperatures. It highlights the typical range of temperatures throughout the month, providing insights into weather trends. In Longmont, December typically has an average temperature of 0°C (33°F), with highs reaching up to 22°C (72°F) and lows dropping to around -16°C (3°F).
JanFebMarAprMayJunJulAugSepOctNovDec303040485668747266494033
Data source: Temperature data for Longmont 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 Longmont

In Longmont in December, the precipitation amount is 15 mm (0.6 in) over the course of 3 days.

December Precipitation Trends in Longmont

The chart displays monthly precipitation patterns in Longmont, 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 Longmont, December typically receives around 15 mm (0.6 inches) of precipitation spread over approximately 3 days.
JanFebMarAprMayJunJulAugSepOctNovDec1926565511942314327382315
Data source: Precipitation data for December generated using information from the Copernicus Climate Change Service.
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December Humidity in Longmont

In Longmont in December, humidity is 85%. With an average temperature of 0°C (33°F), this humidity feels like a heavy blanket, making the air feel colder and more biting, while creating an uncomfortable clamminess that can dampen the thrill of traveling.

December Average Humidity in Longmont

This chart illustrates the average monthly humidity levels in Longmont, 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 Longmont is approximately 85%, offering insight into how humid the weather typically is during this month.
JanFebMarAprMayJunJulAugSepOctNovDec84%86%75%67%67%68%62%63%63%72%80%85%
Data source: Humidity data for December generated using information from the Copernicus Climate Change Service.

December UV Index in Longmont

In Longmont 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 Longmont, you can check the information here.

Maximum UV Index Levels in Longmont for December

The chart shows the monthly maximum UV Index (UVI) for Longmont 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 Longmont typically reaches 3, which falls under the moderate exposure category.
JanFebMarAprMayJunJulAugSepOctNovDec46811111212119643
Data source: Longmont 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 Longmont Compares to Other Months

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

This table compares monthly weather conditions in Longmont, showing how December’s temperature, precipitation, humidity, and UV index levels differ from those of other months.
 TemperaturePrecipitationHumidityUV
January Weather-1°C (30°F)19 mm (0.8 inches)84%moderate
February Weather-1°C (30°F)26 mm (1.0 inches)85%high
March Weather5°C (40°F)56 mm (2.2 inches)75%very high
April Weather9°C (48°F)55 mm (2.2 inches)67%extreme
May Weather13°C (56°F)119 mm (4.7 inches)67%extreme
June Weather20°C (69°F)42 mm (1.6 inches)68%extreme
July Weather23°C (75°F)31 mm (1.2 inches)62%extreme
August Weather22°C (73°F)43 mm (1.7 inches)63%extreme
September Weather19°C (66°F)27 mm (1.1 inches)63%very high
October Weather9°C (49°F)38 mm (1.5 inches)72%high
November Weather4°C (40°F)23 mm (0.9 inches)79%moderate
December Weather0°C (33°F)15 mm (0.6 inches)85%moderate

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