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O'Fallon Weather in September
O'Fallon in September averages 27°C (81°F) during the day and 14°C (57°F) at night. Keep in mind that quite a bit of rainfall is expected this month.
Rainfall in O'Fallon in September
Records from the past 30 years suggest around 9 days of rain, with 105 mm (4.1 in) average for the month. Rainfall intensity is on the higher side this month. Expect more substantial showers rather than light, passing rain.
Temperature in O'Fallon in September
Temperatures in O'Fallon in September top out at 27°C (81°F) and drop to 14°C (57°F) overnight. Overall, the month follows a fairly predictable daily temperature pattern. Nights drop to around 14°C (57°F), which is noticeably cooler than the daytime. A light jacket for the evening is a sensible addition, and the cool nights tend to make sleeping comfortable.
Sunshine in O'Fallon in September
The city usually sees around 235 hours of sunlight, indicating many sunny days , a great month for sightseeing.If you prefer dry days with pleasant temperatures, October typically offers the best circumstances. If you're seeking pleasant, dry and sunny weather somewhere else in the world, our weather planner can help you explore other options.
O'Fallon Temperature in September
Min Temperature
14°C (57°F)
Max Temperature
27°C (81°F)
Chance of Rain
29%
Precipitation
105 mm (4.1 in)
Rainy days
9 days
Humidity
71% *
Sunshine
235 hours *
Percentage Sunshine
63% *
* Data from: St. Louis, the United States of America (48 KM, 29 Miles).
O'Fallon Weather by Month
Pick a month to see the average temperature, rainfall and sunshine in O'Fallon - and find the best time to visit.
Best Places in the United States of America in September
Find out more about the weather in the United States of America and which places have the best travel conditions in this month. See all of the United States of America in September →
perfect weather
pleasant
tolerable
unpleasant
poor
Perfect weather is subjective. On this map perfect weather has been defined with temperatures between 20°C (68°F) and 29°C (84°F) and not too much precipitation (less than 90 mm (3.5 in) a month).
What to Wear in O'Fallon in September
Warm but pleasant conditions in O'Fallon in September. Focus on lightweight, maybe with natural fabrics, cotton blend shirts, comfortable shorts, and breathable footwear. A light cover-up for sun protection is smart too. Expect heavy rainfall, so bring good rain protection and waterproof bags. Don't forget sun protection, sunglasses, sunscreen, and a hat. These are all good ideas with this much sunshine.
What To Do in O'Fallon in September
We rated the following activities from 1 (least suitable) to 10 (best) to do.
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Swimming9/10 -
Cycling7/10 -
Walking7/10 -
Camping6/10 -
Outdoor sports7/10
O'Fallon 3-Day Forecast
More climate data for O'Fallon
Temperature Rainfall Sunshine Humidity
See the full O'Fallon climate overview or explore weather in the United States of America.
Popular in September
Where to go in September - average daytime high across popular destinations.
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