O'Fallon in Winter
In winter (December, January and February), O'Fallon sees average daytime highs around 43°F and overnight lows near 28°F, with 8.3 in of precipitation over about 24 wet days across the season. It is the coldest season of the year and the driest season of the year.
Across winter, daytime highs hold fairly steady around 43°F. The sky is clear or mostly clear about 28% of the time across winter, and the air most often feels dry.
Winter is O'Fallon's weakest 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
- 43°F
- coldest season of the year
- Avg overnight low
- 28°F
- Precipitation
- 8.3 in
- 24 wet days
- Avg wind
- 8 mph
- Travel score
- 0.6
- weakest season of the year
- Months
- Dec · Jan · Feb
Temperature in O'Fallon in Winter
Across winter, daytime highs hold fairly steady around 43°F.
A typical winter day in O'Fallon reaches about 43°F and drops to 28°F overnight. The warmest of the three months is February, the coolest January.
How winter really feels in O'Fallon
Once humidity and wind are folded in, winter brings about 0 days that feel above 90°F and 90 that feel at or below 32°F.
The story in winter is cold — wind chill drags the overnight "feels like" below the raw low.
O'Fallon weather by month
How the three winter months (December, January and February) 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 Winter
The sky is clear or mostly clear about 28% of the time across winter.
Chance of precipitation in Winter
O'Fallon gets around 8.3 in of rain and snow over 24 wet days across winter. The line is the day-by-day chance of measurable precipitation.
Humidity in Winter
Most of winter feels dry — the stacked bands show each day's mix of comfort levels, read off the dew point.
Wind in Winter
Winds average 8 mph across winter.
Sunrise & sunset in Winter
Daylight runs from about 9 h 30 min in early December to 11 hours by late February. The lit band spans sunrise to sunset each day.
Solar energy in Winter
Average shortwave solar energy reaching the ground each day across winter, about 2.4 kWh/m².
Is winter a good time to visit O'Fallon?
Our two travel scores rate winter for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal), averaged across the three months.
winter is a weaker month for outdoor sightseeing in O'Fallon.
What to pack for O'Fallon in Winter
From winter's temperature range, rain chance, sun and wind — what's worth putting in the bag.
In winter, O'Fallon sees daytime highs around 43°F and nights near 28°F. Pack a warm layer and a heavy coat. Worth having: rain gear. About 24 days see rain.
UV index in O'Fallon in Winter
Clear-sky midday UV across winter averages around 3. 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 Winter
Average fine-particle pollution (PM2.5) through the year — so you can see where winter 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.