Climate averages 1991–2020
O'Fallon weather
in January.
A cold, moderately wet month: the coolest and the 3rd driest of the year.
Long-term climate patterns, not a forecast for a particular trip.
January is a cold month in O'Fallon: daytime highs average 4.0°C and nights cool to about -4.4°C. By daytime temperature it is the coolest month of the year.
Expect about 65 mm of rain on roughly 8 days, which makes January a moderately wet month (the 3rd driest of the 12 months). Daylight, from sunrise to sunset, lasts about 9 h 47 min on an average January day.
The nearest other city in this atlas is St. Louis (48 km away). In January its highs average 4.3°C, about as warm as O'Fallon, with 70 mm of rain.
Among the 498 cities listed in the United States, O'Fallon ranks 344th of 498 for the warmest January highs and joint 194th of 498 for the driest January (rainfall, lowest first). The mean January high of those 498 cities is 9.5°C; O'Fallon is 5.4°C cooler than that mean.
From January to February, average highs rise by 2.8°C to 6.8°C, and monthly rainfall falls from 65 mm to 61 mm.
The annual picture
January 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, selected | 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 | 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
January in nearby cities
- St. Louis in JanuaryUnited States · 48 kmHigh 4.3°C · Low -4.3°C · 70 mm rain
- Columbia (Missouri), United States in JanuaryUnited States · 142 kmHigh 3.6°C · Low -5.0°C · 55 mm rain
- Springfield (Illinois), United States in JanuaryUnited States · 143 kmHigh 1.9°C · Low -6.2°C · 61 mm precipitation
- Decatur in JanuaryUnited States · 189 kmHigh 1.8°C · Low -6.3°C · 69 mm precipitation
- Peoria (Illinois), United States in JanuaryUnited States · 230 kmHigh 0.6°C · Low -7.4°C · 53 mm precipitation
- Bloomington (Illinois), United States in JanuaryUnited States · 237 kmHigh 0.7°C · Low -7.3°C · 58 mm precipitation
- Champaign in JanuaryUnited States · 256 kmHigh 1.5°C · Low -6.7°C · 70 mm precipitation
- Springfield (Missouri), United States in JanuaryUnited States · 289 kmHigh 5.9°C · Low -3.1°C · 65 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.