O'Fallon, Missouri Climate by Month
O'Fallon, Missouri, United States
Hot summers and cold winters, with rain spread through the year.
Hot summers and cold winters, with rain spread through the year: that's O'Fallon's climate in short. Afternoon highs range from 40°F (5°C) in January to 90°F (32°C) in July, and January nights average 22°F (-6°C). It gets 39 in (998 mm) of rain a year, spread across the months.
- Warmest month
- 90°F(32°C)
- Average high, July
- Coldest nights
- 22°F(-6°C)
- Average low, January
- Rain per year
- 39 in(998 mm)
- No clear rainy season
- Humidity
- 67%
- Sunniest: July
Best and worst months in O'Fallon
Best for weatherMay, September and October are the best time for weather in O'Fallon: highs near 77°F (25°C) and about 3.8 in (96 mm) of rain a month.
Least pleasantJanuary is the least pleasant month: it's the coldest, with highs of only 40°F (5°C).
Comfort combines how close the afternoon high is to 75°F (24°C) with how much rain falls and how humid it is. See where the weather is best in October.
Temperature and rain through the year
Highs and lows (°F)
Average highAverage low
Rain (in per month)
O'Fallon weather by month
| Month | High | Low | Rain | Humidity | Sun |
|---|---|---|---|---|---|
| JanJanuary | 40°F(5°C) | 22°F(-6°C) | 2.0 in(50 mm) | 68% | 1.8 |
| FebFebruary | 46°F(8°C) | 25°F(-4°C) | 2.0 in(52 mm) | 71% | 2.7 |
| MarMarch | 57°F(14°C) | 34°F(1°C) | 3.2 in(81 mm) | 67% | 3.8 |
| AprApril | 69°F(20°C) | 44°F(7°C) | 3.9 in(98 mm) | 58% | 4.8 |
| MayMayBest | 78°F(26°C) | 55°F(13°C) | 4.8 in(121 mm) | 67% | 5.4 |
| JunJune | 86°F(30°C) | 64°F(18°C) | 3.7 in(95 mm) | 67% | 6.1 |
| JulJuly | 90°F(32°C) | 68°F(20°C) | 4.3 in(108 mm) | 69% | 6.1 |
| AugAugust | 89°F(32°C) | 66°F(19°C) | 3.3 in(84 mm) | 69% | 5.5 |
| SepSeptemberBest | 82°F(28°C) | 57°F(14°C) | 3.5 in(88 mm) | 65% | 4.7 |
| OctOctoberBest | 70°F(21°C) | 45°F(7°C) | 3.1 in(80 mm) | 61% | 3.3 |
| NovNovember | 56°F(13°C) | 35°F(2°C) | 3.1 in(79 mm) | 68% | 2.1 |
| DecDecember | 44°F(7°C) | 26°F(-3°C) | 2.4 in(62 mm) | 72% | 1.6 |
1991–2020 averages. Sun is solar radiation in kWh/m² per day. Highlighted: the most comfortable months.
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