O'Fallon Weather Year-Round — Best Time to Visit
O'Fallon, United States has mild weather year-round. The best time to visit is September (score: 89/100). Annual average high: 18.5°C, total rainfall: 1036mm.
When is the best time to visit O'Fallon?
89
September is the best month to visit O'Fallon with a travel score of 89/100 (Excellent).
Expect highs of 26.3°C, 7 rain days, and 10.1 hours of daily sunshine.
View September weather details →Travel Score by Month
52
Jan
58
Feb
63
Mar
73
Apr
79
May
84
Jun
85
Jul
86
Aug
89
Sep
77
Oct
65
Nov
54
Dec
Excellent (80+)
Good (60-79)
Mixed (40-59)
Poor (<40)
What are the average temperatures in O'Fallon each month?
18.5°C
Avg High
9.1°C
Avg Low
1036mm
Annual Rain
How much rain does O'Fallon get?
O'Fallon receives 1036mm of rain annually. The wettest month is typically May with 122mm, while February is the driest.
What is the weather like each month in O'Fallon?
January
52
4°C
Low: -4°C
8 rain days
Mixed
February
58
7°C
Low: -3°C
7 rain days
Mixed
March
63
13°C
Low: 3°C
10 rain days
Good
April
73
19°C
Low: 8°C
10 rain days
Good
May
79
24°C
Low: 14°C
13 rain days
Good
June
84
29°C
Low: 19°C
10 rain days
Excellent
July
85
31°C
Low: 22°C
10 rain days
Excellent
August
86
30°C
Low: 21°C
9 rain days
Excellent
September
Best time to visit89
26°C
Low: 17°C
7 rain days
Excellent
October
77
20°C
Low: 11°C
8 rain days
Good
November
65
13°C
Low: 4°C
7 rain days
Good
December
54
7°C
Low: -1°C
8 rain days
Mixed
Compare O'Fallon
Popular comparisons:
Planning a Trip to United States?
Don't let a public holiday surprise you — restaurants, shops, and attractions may be closed.
🏛️ 121 countries·📅 Updated yearly·✈️ Free forever
What cities are near O'Fallon?
Data based on 1994–2024 averages · Last updated: 2024-12-31