O'Fallon weather in January

In January, O'Fallon sees average daytime highs of 40°F and overnight lows near 25°F, with 2.9 in of precipitation across 8.3 wet days and about 9.6 hours of daylight. It is the 12th-warmest and 9th-wettest month of the year here.

Day-to-day highs hold fairly steady near 40°F through the month. The sky is clear or mostly clear about 29% of the time in January, and the air most often feels dry.

Daylight stretches from about 9 h 18 min at the start of January to 10 hours by month's end. Set against the rest of the year, January is O'Fallon's 10th-clearest and 4th-windiest month. For the whole year in context, see O'Fallon's year-round climate.

Daytime high
40°
12th warmest
Overnight low
25°
1st coldest
Precipitation
2.9 in
8.3 wet days
Daylight
9 h 36 min
7:21 AM – 4:56 PM
Cloud cover
63%
10th clearest
Wind
8 mph
4th windiest
Solar energy
2.22 kWh/m²
Travel score
0.0
out of 10

O'Fallon is city in St. Clair County, Illinois, United States.

Density
774/km²
people per km²
Founded
1854

Air quality: WHO Ambient Air Quality Database. Density & description: Wikidata (CC0), GeoNames.

Temperature in January

Average highAverage lowShaded bands: 10–90% of days

Day-to-day highs hold fairly steady near 40°F through the month.

A typical January day in O'Fallon reaches about 40°F in the afternoon and slips back to 25°F overnight — a 15°F spread between the day's warmth and the night's chill. On most days the high lands between 25°F and 57°F. Set against its neighbours, January runs about 4°F cooler than December and about 5°F cooler than February.

20°40°60°151015202531
Avg high (°F)Avg low (°F)
14127
24126
34126
44026
54026
64026
74026
84026
94025
104025
114025
124025
134025
144025
154025
164025
174025
184025
194025
204025
214025
224025
234025
244025
254025
264025
274125
284126
294126
304126
314126

How January really feels in O'Fallon

Once humidity and wind are folded in, January averages 0 days that feel above 90°F and 31 that feel at or below 32°F — the comfort signal a plain temperature reading hides.

Days feeling ≥ 90°F
0
heat index over the day's high
Days feeling ≤ 32°F
31
wind chill below the day's low

The story in January is cold — wind chill drags the overnight "feels like" below the raw low.

O'Fallon weather by month

How January compares with the rest of the year at a glance. January is the 12th-warmest and 9th-wettest month here — the current month is highlighted below.

MonthHigh / Low (°F)Rainfall (inches)Wet daysSnow daysDaylight (hours)Travel score
Jan40° / 25°2.98.32.99.60.0
Feb45° / 29°2.67.62.610.51.0
Mar56° / 38°3.810.81.311.73.7
Apr67° / 48°4.811.50.1135.9
May76° / 58°5.113.3014.16.3
Jun85° / 67°4.110.8014.65.2
Jul88° / 71°3.49.8014.44.6
Aug86° / 68°2.99.1013.55.1
Sep80° / 60°3.27.6012.37.0
Oct68° / 49°3.58.40116.7
Nov55° / 38°3.78.70.69.93.6
Dec44° / 29°2.88.529.40.7

Cloud cover in January

ClearMostly clearPartly cloudyMostly cloudyOvercast

The sky is clear or mostly clear about 29% of the time in January.

Beyond those clear spells, partly cloudy skies cover about 12% of January, with mostly cloudy or overcast conditions the remaining 59%.

0%25%50%75%100%151015202531
Clearer (%)Cloudier (%)
13862
23862
33862
43763
53763
63862
73961
83961
93961
103961
113961
124060
134060
144060
154060
164159
174159
184159
194258
204258
214258
224456
234456
244456
254357
264357
274357
284456
294456
304258
314258

Chance of precipitation in January

Any precipitationSnow

O'Fallon gets around 2.9 in of rain and snow over 8.3 wet days in January. The line is the day-by-day chance of measurable precipitation.

Day to day, the chance of measurable precipitation averages around 26% and peaks near 29% on the wettest days, and about 3 days bring snow.

0%10%20%30%40%151015202531
Rain chance (%)Snow chance (%)
1268
2268
3279
4279
5289
6289
7299
8299
9299
10299
11289
12289
13289
14289
15289
16279
17279
18279
19269
20269
21259
22259
232510
242410
252410
262410
272410
282310
292310
302310
31239

Humidity in January

DryComfortableHumidMuggyOppressiveMiserable

Most of January feels dry — the stacked bands show each day's mix of comfort levels, read off the dew point.

By dew point, January lands in the dry band about 99% of days. It rarely turns muggy — the humid and sticky bands barely register.

0%25%50%75%100%151015202531
Dry (%)Comfortable (%)
1982
2982
3982
4982
5982
6982
7982
8982
9982
10982
11991
12991
13991
14991
15991
16991
171000
181000
191000
201000
211000
221000
231000
241000
251000
261000
271000
281000
291000
301000
311000

Wind in January

Winds average 8 mph in January.

Across January, daily wind ranges from about 8 mph on the calmest days to 8 mph at its breeziest. It stays fairly steady from day to day.

0246810151015202531
Wind speed (mph)Feels
18light breeze
28light breeze
38light breeze
48light breeze
58light breeze
68light breeze
78light breeze
88light breeze
98light breeze
108light breeze
118light breeze
128light breeze
138light breeze
148light breeze
158light breeze
168light breeze
178light breeze
188light breeze
198light breeze
208light breeze
218light breeze
228light breeze
238light breeze
248light breeze
258light breeze
268light breeze
278light breeze
288light breeze
298light breeze
308light breeze
318light breeze

Sunrise & sunset in January

DaylightNight

Daylight runs from about 9 h 18 min at the start of January to 10 hours by month's end. The lit band spans sunrise to sunset each day.

Days grow by about 42 minutes over January. Sunrise moves from 7:22 AM to 7:13 AM, and sunset from 4:43 PM to 5:12 PM.

12 AM4 AM8 AM12 PM4 PM8 PM12 AM151015202531
Daylight (h)Sunrise (AM)Sunset (PM)
19.37:224:43
29.47:234:44
39.47:234:45
49.47:234:46
59.47:234:46
69.47:234:47
79.47:234:48
89.47:234:49
99.47:234:50
109.57:234:51
119.57:234:52
129.57:224:53
139.57:224:53
149.57:224:54
159.67:224:55
169.67:214:56
179.67:214:57
189.67:214:58
199.77:204:59
209.77:205:01
219.77:205:02
229.77:195:03
239.87:195:04
249.87:185:05
259.87:175:06
269.87:175:07
279.97:165:08
289.97:165:09
299.97:155:10
3010.07:145:11
3110.07:135:12

Solar energy in January

Daily solar energy (kWh/m²)

Average shortwave solar energy reaching the ground each day in January, about 2.22 kWh/m².

For context, solar energy here swings from a low near 1.91 kWh/m² to a high of 6.47 kWh/m² in June across the year — January's 2.22 kWh/m² sits near the bottom.

0123151015202531
Solar energy (kWh/m²)Level
11.9Dim
22.0Dim
32.0Dim
42.0Dim
52.0Dim
62.0Moderate
72.0Moderate
82.0Moderate
92.0Moderate
102.1Moderate
112.1Moderate
122.1Moderate
132.1Moderate
142.1Moderate
152.2Moderate
162.2Moderate
172.2Moderate
182.3Moderate
192.3Moderate
202.3Moderate
212.4Moderate
222.4Moderate
232.4Moderate
242.4Moderate
252.5Moderate
262.5Moderate
272.5Moderate
282.6Moderate
292.6Moderate
302.6Moderate
312.6Moderate
Planning a trip in January

Is January a good time to visit O'Fallon?

Our two travel scores rate January for general sightseeing and for beach or pool weather — 0 (poor) to 10 (ideal).

0.0
Sightseeing
12th-best month of the year
0.0
Beach & pool
10th-best month of the year

January is a weaker month for outdoor sightseeing in O'Fallon.

What to pack for O'Fallon in January

From January's temperature range, rain chance, sun and wind — what's worth putting in the bag.

In January, O'Fallon sees daytime highs around 40°F and nights near 25°F. Pack a warm layer and a heavy coat. Worth having: rain gear. About 8 days see rain.

a warm layera heavy coatrain gear

UV index in O'Fallon in January

LowModerateHighVery highExtreme

Clear-sky midday UV in January peaks around 2. 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.

025710JanFebMarAprMayJunJulAugSepOctNovDecModerateHighVery highHighModerateJun 22UV 9Dec 23UV 2
UV index (midday)Level
Jan2Moderate
Feb3Moderate
Mar5High
Apr7High
May8Very high
Jun9Very high
Jul9Very high
Aug8Very high
Sep7High
Oct4Moderate
Nov3Moderate
Dec2Low

Air quality in O'Fallon in January

GoodModeratePoorUnhealthyVery unhealthy

Average fine-particle pollution (PM2.5) through the year — so you can see where January 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).

01020JanFebMarAprMayJunJulAugSepOctNovDecGoodModerateGoodJul 1418 µg/m³Oct 238 µg/m³
PM2.5 (µg/m³)Level
Jan9Good
Feb12Good
Mar12Good
Apr11Good
May14Moderate
Jun16Moderate
Jul18Moderate
Aug15Moderate
Sep12Moderate
Oct8Good
Nov8Good
Dec9Good
Location & terrain

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.

2 miles
177 ft
10 miles
295 ft
50 miles
958 ft
treesgrasslandcroplandartificial surfacesbare terrainwater
January weather nearby: Fairview Heights 4.3 mi · Belleville 6.2 mi · Collinsville 6.8 mi · East Saint Louis 13 mi · Granite City 15 mi · Edwardsville 16 mi · St. Louis 16 mi · Lemay 21 mi

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
Protestant 47%unaffiliated 23%Roman Catholic 21%Jewish 2%

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. UV index is derived from CAMS (Copernicus Atmosphere Monitoring Service) clear-sky UV data — contains modified Copernicus Atmosphere Monitoring Service information. Monthly air-quality (PM2.5) seasonality is from the CAMS EAC4 reanalysis (Copernicus Atmosphere Monitoring Service), scaled to the WHO annual mean where available. Topography is sampled from the Copernicus DEM GLO-90 elevation model (© ESA/Airbus) and ESA WorldCover 2021 land cover (CC BY 4.0).