Last updated: June 24, 2025
In Boulder, United States, the average temperature in December hovers around -8°C (19°F). However, temperatures can plummet to a minimum of -28°C (-17°F) or rise to a surprising maximum of 15°C (59°F). Expect about 32 mm (1.3 in) of precipitation spread across 8 days, contributing to an average humidity of 90%. Prepare for a truly chilly experience!
In December in Boulder, the average temperature is -8°C (19°F). The maximum can reach 15°C (59°F), while the minimum can drop as low as -28°C (-17°F). Travelers should be prepared for a wide range of temperatures and dress accordingly for both cold and milder conditions.
In Boulder in December, the precipitation amount is 32 mm (1.3 in) over the course of 8 days.
In Boulder in December humidity is 90%. With an average temperature of -8°C (19°F), this humidity feels like an icy mist enveloping you, making every breath feel crisp yet heavy, creating an uncomfortable chill that penetrates your clothes and slows your movement as you travel.
In Boulder 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 Boulder, you can visit Hourly UV Index in Boulder.
UV Risk Categories
Weather in Boulder varies notably across the year, with each month offering distinct climate conditions. This page compares December’s weather to other months in Boulder, focusing on differences in temperature, rainfall, humidity, and UV levels.
| Temperature | Precipitation | Humidity | UV | |
|---|---|---|---|---|
| January Weather | -8°C (18°F) | 23 mm (0.9 inches) | 87% | moderate |
| February Weather | -9°C (16°F) | 55 mm (2.2 inches) | 88% | moderate |
| March Weather | -2°C (28°F) | 40 mm (1.6 inches) | 83% | high |
| April Weather | 1°C (34°F) | 68 mm (2.7 inches) | 78% | very high |
| May Weather | 8°C (46°F) | 92 mm (3.6 inches) | 76% | very high |
| June Weather | 14°C (57°F) | 112 mm (4.4 inches) | 78% | extreme |
| July Weather | 18°C (65°F) | 44 mm (1.7 inches) | 77% | very high |
| August Weather | 17°C (64°F) | 39 mm (1.5 inches) | 71% | very high |
| September Weather | 12°C (54°F) | 43 mm (1.7 inches) | 68% | very high |
| October Weather | 3°C (38°F) | 44 mm (1.7 inches) | 72% | moderate |
| November Weather | -3°C (28°F) | 34 mm (1.3 inches) | 84% | moderate |
| December Weather | -8°C (19°F) | 32 mm (1.3 inches) | 90% | low |