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.

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For a detailed overview over the year and the best time to visit the United States of America, check out our O'Fallon's climate page.

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).

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.

Swimming

9/10

Cycling

7/10

Walking

7/10

Camping

6/10

Outdoor sports

7/10

Select a Month

Check the conditions for any month of the year.

• January
• February
• March
• April

• May
• June
• July
• August

• September
• October
• November
• December

For a detailed overview over the year and the best time to visit the United States of America, check out our O'Fallon's climate page.

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.