Climate averages 1991–2020
Longmont weather
in December.
A cold, fairly dry month: the coolest and the driest of the year.
Long-term climate patterns, not a forecast for a particular trip.
December is a cold month in Longmont: daytime highs average 4.2°C and nights cool to about -8.1°C. By daytime temperature it is the coolest month of the year.
Expect about 18 mm of rain on roughly 5 days, which makes December a fairly dry month (the driest month of the year). Daylight, from sunrise to sunset, lasts about 9 h 22 min on an average December day.
The nearest other city in this atlas is Boulder (22 km away). In December its highs average 4.0°C, about as warm as Longmont, with 23 mm of rain.
Among the 498 cities listed in the United States, Longmont ranks joint 387th of 498 for the warmest December highs and joint 10th of 498 for the driest December (rainfall, lowest first). The mean December high of those 498 cities is 10.5°C; Longmont is 6.3°C cooler than that mean.
From December to January, average highs rise by 0.3°C to 4.5°C, and monthly rainfall rises from 18 mm to 19 mm.
The annual picture
December in context
Monthly rainfall
Average total · mmAverages from hourly ERA5 reanalysis data. Actual weather varies from year to year. How these numbers are calculated
Every month, side by side
Longmont climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 4.5°C-8.4°C | -8.4°C | 19 | 4.7 | 9.710 h |
| February | 5.9°C-7.6°C | -7.6°C | 20 | 5.3 | 10.611 h |
| March | 11.0°C-3.9°C | -3.9°C | 42 | 7.3 | 11.912 h |
| April | 14.8°C0.4°C | 0.4°C | 67 | 9.5 | 13.213 h |
| May | 19.9°C5.9°C | 5.9°C | 87 | 11.7 | 14.414 h |
| June | 26.0°C11.4°C | 11.4°C | 53 | 8.4 | 15.015 h |
| July | 29.5°C15.0°C | 15.0°C | 42 | 7.3 | 14.715 h |
| August | 28.3°C14.3°C | 14.3°C | 39 | 6.7 | 13.814 h |
| September | 24.2°C9.9°C | 9.9°C | 39 | 5.9 | 12.512 h |
| October | 16.8°C3.2°C | 3.2°C | 41 | 6.5 | 11.211 h |
| November | 9.4°C-3.6°C | -3.6°C | 28 | 5.8 | 10.010 h |
| December, selected | 4.2°C-8.1°C | -8.1°C | 18 | 4.5 | 9.49 h |
Rainfall is the average of the 30 separate monthly totals. A rain day is a local calendar day with at least 1 mm of precipitation. Daylight is the calculated sunrise-to-sunset length, not measured sunshine.
Compare places
December in nearby cities
- Boulder in DecemberUnited States · 22 kmHigh 4.0°C · Low -8.8°C · 23 mm rain
- Loveland in DecemberUnited States · 26 kmHigh 4.2°C · Low -8.4°C · 16 mm rain
- Thornton in DecemberUnited States · 35 kmHigh 4.0°C · Low -9.7°C · 21 mm rain
- Westminster (Colorado), United States in DecemberUnited States · 37 kmHigh 4.2°C · Low -9.8°C · 21 mm rain
- Arvada in DecemberUnited States · 41 kmHigh 4.4°C · Low -9.7°C · 21 mm rain
- Greeley in DecemberUnited States · 44 kmHigh 4.9°C · Low -6.8°C · 11 mm rain
- Fort Collins in DecemberUnited States · 47 kmHigh 4.2°C · Low -7.8°C · 16 mm rain
- Denver in DecemberUnited States · 49 kmHigh 4.4°C · Low -9.6°C · 21 mm rain
Read the numbers correctly
Climate, not a promise.
These patterns help compare months. They cannot tell you the weather on a specific day of your trip.
Sources, method and limitsHow these numbers are made (what the highs, lows and rain days mean, the sources and the model cell used for Longmont) is explained once on the Longmont year overview and on the Sources, method and limits page.