O'Fallon in Fall
In fall (September, October and November), O'Fallon sees average daytime highs around 68°F and overnight lows near 49°F, with 10.4 in of precipitation over about 25 wet days across the season. It is the 2nd-warmest season and the 3rd-wettest season.
Over the season highs ease from about 84°F in early September to 50°F by late November. The sky is clear or mostly clear about 44% of the time across fall, and the air most often feels dry.
Fall is O'Fallon's best season of the year to visit on our travel score. For the whole year in context, see O'Fallon's year-round climate.
- Avg daytime high
- 68°F
- 2nd-warmest season
- Avg overnight low
- 49°F
- Precipitation
- 10.4 in
- 25 wet days
- Avg wind
- 7 mph
- Travel score
- 5.8
- best season of the year
- Months
- Sep · Oct · Nov
Temperature in O'Fallon in Fall
Over the season highs ease from about 84°F in early September to 50°F by late November.
A typical fall day in O'Fallon reaches about 68°F and drops to 49°F overnight. The warmest of the three months is September, the coolest November.
How fall really feels in O'Fallon
Once humidity and wind are folded in, fall brings about 0 days that feel above 90°F and 15 that feel at or below 32°F.
The story in fall is cold — wind chill drags the overnight "feels like" below the raw low.
O'Fallon weather by month
How the three fall months (September, October and November) compare with the rest of the year — the season's months are highlighted.
| Month | High / Low (°F) | Rainfall (inches) | Wet days | Snow days | Daylight (hours) | Travel score |
|---|---|---|---|---|---|---|
| Jan | 40° / 25° | 2.9 | 8.3 | 2.9 | 9.6 | 0.0 |
| Feb | 45° / 29° | 2.6 | 7.6 | 2.6 | 10.5 | 1.0 |
| Mar | 56° / 38° | 3.8 | 10.8 | 1.3 | 11.7 | 3.7 |
| Apr | 67° / 48° | 4.8 | 11.5 | 0.1 | 13 | 5.9 |
| May | 76° / 58° | 5.1 | 13.3 | 0 | 14.1 | 6.3 |
| Jun | 85° / 67° | 4.1 | 10.8 | 0 | 14.6 | 5.2 |
| Jul | 88° / 71° | 3.4 | 9.8 | 0 | 14.4 | 4.6 |
| Aug | 86° / 68° | 2.9 | 9.1 | 0 | 13.5 | 5.1 |
| Sep | 80° / 60° | 3.2 | 7.6 | 0 | 12.3 | 7.0 |
| Oct | 68° / 49° | 3.5 | 8.4 | 0 | 11 | 6.7 |
| Nov | 55° / 38° | 3.7 | 8.7 | 0.6 | 9.9 | 3.6 |
| Dec | 44° / 29° | 2.8 | 8.5 | 2 | 9.4 | 0.7 |
Cloud cover in Fall
The sky is clear or mostly clear about 44% of the time across fall.
Chance of precipitation in Fall
O'Fallon gets around 10.4 in of rain and snow over 25 wet days across fall. The line is the day-by-day chance of measurable precipitation.
Humidity in Fall
Most of fall feels dry — the stacked bands show each day's mix of comfort levels, read off the dew point.
Wind in Fall
Winds average 7 mph across fall.
Sunrise & sunset in Fall
Daylight runs from about 12 h 54 min in early September to 9 h 30 min by late November. The lit band spans sunrise to sunset each day.
Solar energy in Fall
Average shortwave solar energy reaching the ground each day across fall, about 3.6 kWh/m².
Is fall a good time to visit O'Fallon?
Our two travel scores rate fall for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal), averaged across the three months.
fall is a reasonable time to visit O'Fallon for sightseeing.
What to pack for O'Fallon in Fall
From fall's temperature range, rain chance, sun and wind — what's worth putting in the bag.
In fall, O'Fallon sees daytime highs around 68°F and nights near 49°F. Worth packing: light clothes, a warm layer, rain gear and sun protection. About 25 days see rain.
UV index in O'Fallon in Fall
Clear-sky midday UV across fall averages around 5 — enough to warrant sun protection. The full-year curve, shaded by WHO exposure level, is below.
Under clear skies, the midday UV index in O'Fallon peaks around June 22 at about 9 (very high) — sunscreen, a hat and midday shade are essential. It bottoms out near December 23 at about 2 (moderate).
The index reaches 3 or more — the level where the WHO recommends sun protection — in 10 months of the year.
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| UV index (midday) | 2 | 3 | 5 | 7 | 8 | 9 | 9 | 8 | 7 | 4 | 3 | 2 |
| Level | Moderate | Moderate | High | High | Very high | Very high | Very high | Very high | High | Moderate | Moderate | Low |
| UV index (midday) | Level | |
|---|---|---|
| Jan | 2 | Moderate |
| Feb | 3 | Moderate |
| Mar | 5 | High |
| Apr | 7 | High |
| May | 8 | Very high |
| Jun | 9 | Very high |
| Jul | 9 | Very high |
| Aug | 8 | Very high |
| Sep | 7 | High |
| Oct | 4 | Moderate |
| Nov | 3 | Moderate |
| Dec | 2 | Low |
Air quality in O'Fallon in Fall
Average fine-particle pollution (PM2.5) through the year — so you can see where fall falls, not just the annual average.
Air quality in O'Fallon is worst in July — around 18 µg/m³ PM2.5 (moderate), about 2.3× the cleanest month (October, 8 µg/m³).
Modeled monthly averages (CAMS reanalysis, 2015–2024).
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| PM2.5 (µg/m³) | 9 | 12 | 12 | 11 | 14 | 16 | 18 | 15 | 12 | 8 | 8 | 9 |
| Level | Good | Good | Good | Good | Moderate | Moderate | Moderate | Moderate | Moderate | Good | Good | Good |
| PM2.5 (µg/m³) | Level | |
|---|---|---|
| Jan | 9 | Good |
| Feb | 12 | Good |
| Mar | 12 | Good |
| Apr | 11 | Good |
| May | 14 | Moderate |
| Jun | 16 | Moderate |
| Jul | 18 | Moderate |
| Aug | 15 | Moderate |
| Sep | 12 | Moderate |
| Oct | 8 | Good |
| Nov | 8 | Good |
| Dec | 9 | Good |
Where is O'Fallon?
O'Fallon sits at 38.6°N, 89.9°W, 548 ft above sea level, in United States. The nearest listed city is Fairview Heights, 4.3 mi away.
Topography around O'Fallon
How much the land rises and falls, and what covers it, within 2, 10 and 50 miles of O'Fallon.
Within 2 miles, the terrain around O'Fallon has only modest variations in elevation — a maximum elevation change of 177 ft around an average of 548 ft above sea level; within 10 miles, only modest variations in elevation — a maximum elevation change of 295 ft; within 50 miles, significant variations in elevation — a maximum elevation change of 958 ft.
The land around O'Fallon is covered by trees (37%), artificial surfaces (23%) and grassland (21%) within 2 miles, cropland (41%) and trees (36%) within 10 miles, and cropland (48%) and trees (39%) within 50 miles.
United States travel facts
- Power plugs
- Type A / B
- 120 V · 60 Hz
- Prices
- ≈ 100% of US
- price level, 2025
- GDP per capita
- $90,027
- 2025
- Happiness
- 6.8 / 10
- World Happiness, 2025
- Safe drinking water
- 98%
- of population, 2024
- Homicide rate
- 5.8
- per 100k, 2023
- Road deaths
- 12.7
- per 100k/yr, 2019
- Income group
- High
- World Bank
- Religion
Sources: World Bank, US State Department, World Happiness Report, WHO/UNICEF, EF EPI, CIA World Factbook.
Data sources
Temperature, precipitation, cloud, humidity, wind and solar figures are a 1991–2020 climatology for O'Fallon (38.5923°, -89.9112°, elevation 548 ft), computed from hourly ERA5 reanalysis — contains modified Copernicus Climate Change Service information. Sun figures are astronomical calculations, not observations. City data © GeoNames, CC BY 4.0. Map outlines from Natural Earth (public domain); interactive map © Google.