Last updated: June 24, 2025
In Helena, United States, the average temperature in December hovers around -6°C (21°F), with extremes ranging from a chilly -25°C (-13°F) to a rare high of 16°C (61°F). Expect 33 mm (1.3 in) of precipitation over approximately 8 days throughout the month, coupled with a high average humidity of 90%. Prepare for a wintery blend of cold and moisture!
In December in Helena, the average temperature is -6°C (21°F). The maximum can reach 16°C (61°F) and the minimum can dip as low as -25°C (-13°F). Travelers should prepare for a wide range of temperatures and dress accordingly to enjoy their visit.
In Helena in December, the precipitation amount is 33 mm (1.3 in) during a span of 8 days.
In Helena in December humidity is 90%. With an average temperature of -6°C (21°F), this humidity feels like a heavy, icy mist that clings to your skin, making every breath feel sharp and cold, which can be quite challenging for traveling.
In Helena 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 Helena, you can visit Hourly UV Index in Helena.
UV Risk Categories
Weather in Helena varies notably across the year, with each month offering distinct climate conditions. This page compares December’s weather to other months in Helena, focusing on differences in temperature, rainfall, humidity, and UV levels.
| Temperature | Precipitation | Humidity | UV | |
|---|---|---|---|---|
| January Weather | -7°C (20°F) | 23 mm (0.9 inches) | 87% | moderate |
| February Weather | -9°C (16°F) | 51 mm (2.0 inches) | 88% | moderate |
| March Weather | -2°C (29°F) | 38 mm (1.5 inches) | 83% | high |
| April Weather | 2°C (36°F) | 67 mm (2.7 inches) | 78% | very high |
| May Weather | 9°C (48°F) | 88 mm (3.5 inches) | 76% | very high |
| June Weather | 14°C (58°F) | 107 mm (4.2 inches) | 78% | extreme |
| July Weather | 19°C (67°F) | 31 mm (1.2 inches) | 77% | very high |
| August Weather | 18°C (65°F) | 34 mm (1.3 inches) | 71% | very high |
| September Weather | 13°C (55°F) | 44 mm (1.7 inches) | 68% | very high |
| October Weather | 4°C (40°F) | 41 mm (1.6 inches) | 72% | moderate |
| November Weather | -1°C (30°F) | 33 mm (1.3 inches) | 84% | moderate |
| December Weather | -6°C (21°F) | 33 mm (1.3 inches) | 90% | low |