Climate averages 1991–2020
O'Fallon weather
in July.
A hot, moderately wet month: the warmest and the 6th driest of the year.
Long-term climate patterns, not a forecast for a particular trip.
July is a hot month in O'Fallon: daytime highs average 30.8°C and nights cool to about 21.6°C. By daytime temperature it is the warmest month of the year.
Expect about 82 mm of rain on roughly 10 days, which makes July a moderately wet month (the 6th driest of the 12 months). Daylight, from sunrise to sunset, lasts about 14 h 36 min on an average July day.
The nearest other city in this atlas is St. Louis (48 km away). In July its highs average 31.0°C, about as warm as O'Fallon, with 86 mm of rain.
Among the 498 cities listed in the United States, O'Fallon ranks joint 211th of 498 for the warmest July highs and joint 261st of 498 for the driest July (rainfall, lowest first). The mean July high of those 498 cities is 30.3°C; O'Fallon is 0.5°C warmer than that mean.
From July to August, average highs fall by 0.7°C to 30.1°C, and monthly rainfall falls from 82 mm to 76 mm.
The annual picture
July 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, selected | 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
July in nearby cities
- St. Louis in JulyUnited States · 48 kmHigh 31.0°C · Low 21.6°C · 86 mm rain
- Columbia (Missouri), United States in JulyUnited States · 142 kmHigh 31.1°C · Low 21.6°C · 93 mm rain
- Springfield (Illinois), United States in JulyUnited States · 143 kmHigh 29.1°C · Low 20.2°C · 91 mm rain
- Decatur in JulyUnited States · 189 kmHigh 28.8°C · Low 19.9°C · 91 mm rain
- Peoria (Illinois), United States in JulyUnited States · 230 kmHigh 28.8°C · Low 20.1°C · 96 mm rain
- Bloomington (Illinois), United States in JulyUnited States · 237 kmHigh 28.2°C · Low 19.3°C · 98 mm rain
- Champaign in JulyUnited States · 256 kmHigh 28.3°C · Low 19.3°C · 92 mm rain
- Springfield (Missouri), United States in JulyUnited States · 289 kmHigh 31.2°C · Low 21.3°C · 89 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.