Annual mean 14°C · wettest around April · prevailing wind SW
Warmest
29.8 °C
Coldest
0.5 °C
Wettest
42%
Windiest
5.3 m/s
Prevailing
SW
4.0 m/s average
When this place is good five ratings · thirty-six ten-day sections · click a cell to read it
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Every reading
bars actual · line feels-like, °Cchance of rain, %wind speed, m/ssky covered, %
The average temperature in O'Fallon over the whole year is 14°C. July is the hottest month, with highs of about 30°C; January is the coldest, with lows of about -2°C. O'Fallon has no sharply defined rainy season: the chance of rain on a given day runs from 35% in September, the driest month, to 43% in April, the wettest. Winds in O'Fallon are highest in March, averaging 3.9 m/s (14 km/h), and lightest in August, at 1.9 m/s (7 km/h). The prevailing wind is from the SW. The clearest skies in O'Fallon come in June, when the sky is typically 26% covered; January is the cloudiest month, at 52%.
Month by month O'Fallon climate by month: average temperatures year round · click a month to read it
Month
High
Low
Feels like
Chance of rain
Cloud
Wind
Being outside
Sun
Walking
January
2°C
-2°C
-4°C
38%
52%
3.4 m/s
1
0
10
February
6°C
-0°C
1°C
38%
43%
3.4 m/s
8
0
26
March
11°C
5°C
7°C
42%
47%
3.9 m/s
15
0
44
April
17°C
9°C
13°C
43%
40%
3.8 m/s
40
5
62
May
23°C
15°C
21°C
43%
40%
3.0 m/s
61
31
51
June
28°C
21°C
29°C
40%
26%
2.5 m/s
39
58
15
July
30°C
22°C
32°C
40%
28%
2.0 m/s
17
53
4
August
28°C
20°C
30°C
39%
30%
1.9 m/s
32
56
10
September
26°C
16°C
26°C
35%
27%
2.1 m/s
53
53
29
October
19°C
10°C
16°C
39%
38%
2.8 m/s
50
15
61
November
11°C
4°C
7°C
39%
37%
3.0 m/s
18
1
48
December
6°C
1°C
1°C
39%
45%
3.2 m/s
3
0
23
High and low are the warmest and coolest of four readings a day — midnight, 6am, noon and 6pm — so a true overnight low can sit a degree or two under them. Chance of rain, cloud and wind are the day’s average; feels-like and the three ratings (each out of 100: Good from 55, Ideal from 80) are read at midday.
Seasons, and the year in short O'Fallon weather by season
Year round, O'Fallon has days of about 2°C at their warmest in January, its coolest month, and 30°C in July, its warmest; the coolest hours of the day run from -2°C to 22°C through the year, and the average temperature over the year is 14°C around the clock. Rain is most likely around April and least likely around September. Every figure here is a decade of observations blended into one representative year, so it reads as what this date is usually like, not a forecast for one particular day.
O'Fallon weather in winterDecember to February
High 4°CLow -1°CRain 38%
Winter in O'Fallon has typical daily highs of about 4°C and lows of about -1°C, with a 38% chance of rain on a given day.
O'Fallon weather in springMarch to May
High 17°CLow 10°CRain 43%
Spring in O'Fallon has typical daily highs of about 17°C and lows of about 10°C, with a 43% chance of rain on a given day.
O'Fallon weather in summerJune to August
High 29°CLow 21°CRain 40%
Summer in O'Fallon has typical daily highs of about 29°C and lows of about 21°C, with a 40% chance of rain on a given day.
O'Fallon weather in autumnSeptember to November
High 19°CLow 10°CRain 38%
Autumn in O'Fallon has typical daily highs of about 19°C and lows of about 10°C, with a 38% chance of rain on a given day.
When is the rainy season in O'Fallon?
O'Fallon has no sharply defined rainy season: the chance of rain on a given day runs from 35% in September, the driest month, to 43% in April, the wettest.
What time of year is O'Fallon windiest?
Winds in O'Fallon are highest in March, averaging 3.9 m/s (14 km/h), and lightest in August, at 1.9 m/s (7 km/h). The prevailing wind is from the SW.
What is the average temperature in O'Fallon year round?
The average temperature in O'Fallon over the whole year is 14°C. July is the hottest month, with highs of about 30°C; January is the coldest, with lows of about -2°C.