Annual mean 14°C · wettest around April · prevailing wind SW
Warmest
29.7 °C
Coldest
1.0 °C
Wettest
40%
Windiest
5.2 m/s
Prevailing
SW
4.1 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 33% 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 July, at 2.1 m/s (8 km/h). The prevailing wind is from the SW. The clearest skies in O'Fallon come in September, when the sky is typically 28% covered; January is the cloudiest month, at 55%.
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
-3°C
33%
55%
3.6 m/s
1
0
10
February
6°C
-0°C
1°C
33%
47%
3.6 m/s
7
0
25
March
12°C
5°C
7°C
40%
49%
3.9 m/s
15
0
43
April
17°C
9°C
13°C
43%
44%
3.8 m/s
40
5
61
May
23°C
15°C
21°C
41%
44%
3.0 m/s
59
30
50
June
28°C
21°C
29°C
35%
31%
2.6 m/s
38
54
14
July
30°C
22°C
32°C
38%
33%
2.1 m/s
16
51
4
August
28°C
20°C
30°C
37%
33%
2.1 m/s
30
54
9
September
27°C
16°C
26°C
33%
28%
2.1 m/s
51
53
27
October
19°C
10°C
16°C
36%
37%
2.8 m/s
49
15
60
November
11°C
4°C
7°C
38%
40%
3.1 m/s
17
1
45
December
6°C
1°C
1°C
36%
48%
3.3 m/s
3
0
22
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 34%
Winter in O'Fallon has typical daily highs of about 4°C and lows of about -1°C, with a 34% chance of rain on a given day.
O'Fallon weather in springMarch to May
High 17°CLow 10°CRain 41%
Spring in O'Fallon has typical daily highs of about 17°C and lows of about 10°C, with a 41% chance of rain on a given day.
O'Fallon weather in summerJune to August
High 29°CLow 21°CRain 37%
Summer in O'Fallon has typical daily highs of about 29°C and lows of about 21°C, with a 37% chance of rain on a given day.
O'Fallon weather in autumnSeptember to November
High 19°CLow 10°CRain 35%
Autumn in O'Fallon has typical daily highs of about 19°C and lows of about 10°C, with a 35% 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 33% 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 July, at 2.1 m/s (8 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.