Climate averages 1991–2020
O'Fallon weather
in December.
A cold, moderately wet month: the 11th warmest and the 2nd driest of the year.
Long-term climate patterns, not a forecast for a particular trip.
December is a cold month in O'Fallon: daytime highs average 6.1°C and nights cool to about -1.7°C. By daytime temperature it is the 11th warmest of the 12 months.
Expect about 62 mm of rain on roughly 8 days, which makes December a moderately wet month (the 2nd driest of the 12 months). Daylight, from sunrise to sunset, lasts about 9 h 30 min on an average December day.
The nearest other city in this atlas is St. Louis (48 km away). In December its highs average 6.3°C, about as warm as O'Fallon, with 65 mm of rain.
Among the 498 cities listed in the United States, O'Fallon ranks joint 326th of 498 for the warmest December highs and joint 226th of 498 for the driest December (rainfall, lowest first). The mean December high of those 498 cities is 10.5°C; O'Fallon is 4.5°C cooler than that mean.
From December to January, average highs fall by 2.1°C to 4.0°C, and monthly rainfall rises from 62 mm to 65 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
O'Fallon climate table
| Month | Average highHigh / low | Average low | Rainfall mm/month | Rain days ≥1 mm/day | Daylight hours/dayDaylight h/day |
|---|---|---|---|---|---|
| January | 4.0°C-4.4°C | -4.4°C | 65 | 7.7 | 9.810 h |
| February | 6.8°C-2.6°C | -2.6°C | 61 | 7.7 | 10.711 h |
| March | 12.6°C2.6°C | 2.6°C | 92 | 10.6 | 11.912 h |
| April | 18.7°C8.5°C | 8.5°C | 114 | 11.3 | 13.213 h |
| May | 23.8°C14.3°C | 14.3°C | 123 | 13.3 | 14.314 h |
| June | 28.6°C19.3°C | 19.3°C | 101 | 11.0 | 14.815 h |
| July | 30.8°C21.6°C | 21.6°C | 82 | 9.9 | 14.615 h |
| August | 30.1°C20.9°C | 20.9°C | 76 | 9.1 | 13.714 h |
| September | 26.0°C16.7°C | 16.7°C | 81 | 7.6 | 12.512 h |
| October | 19.5°C10.4°C | 10.4°C | 84 | 8.4 | 11.211 h |
| November | 12.0°C3.7°C | 3.7°C | 89 | 8.3 | 10.110 h |
| December, selected | 6.1°C-1.7°C | -1.7°C | 62 | 7.8 | 9.510 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
- St. Louis in DecemberUnited States · 48 kmHigh 6.3°C · Low -1.7°C · 65 mm rain
- Columbia (Missouri), United States in DecemberUnited States · 142 kmHigh 5.8°C · Low -2.0°C · 59 mm rain
- Springfield (Illinois), United States in DecemberUnited States · 143 kmHigh 4.4°C · Low -3.1°C · 59 mm rain
- Decatur in DecemberUnited States · 189 kmHigh 4.3°C · Low -3.1°C · 63 mm rain
- Peoria (Illinois), United States in DecemberUnited States · 230 kmHigh 3.3°C · Low -4.0°C · 57 mm rain
- Bloomington (Illinois), United States in DecemberUnited States · 237 kmHigh 3.3°C · Low -4.1°C · 59 mm rain
- Champaign in DecemberUnited States · 256 kmHigh 3.9°C · Low -3.5°C · 65 mm rain
- Springfield (Missouri), United States in DecemberUnited States · 289 kmHigh 7.2°C · Low -1.1°C · 68 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 O'Fallon) is explained once on the O'Fallon year overview and on the Sources, method and limits page.