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Contents
- Weather in January
- Weather in February
- Weather in March
- Weather in April
- Weather in May
- Weather in June
- Weather in July
- Weather in August
- Weather in September
- Weather in October
- Weather in November
- Weather in December
- Frequently asked questions
- Average temperature
- Average pressure
- Average wind speed
- Average humidity
- Average rainfall
- Average rainfall days
- Average snowfall
- Average snowfall days
- Average daylight
- Average sunshine
- Average sunshine days
- Average UV index
- Average cloud cover
- Average visibility
Weather in January
January, like December, in O'Fallon, Illinois, is a wintry winter month, with temperature in the range of an average high of 37.8°F (3.2°C) and an average low of 24.6°F (-4.1°C). O'Fallon's temperature records reveal January as the coldest month, marked by average highs of 37.8°F (3.2°C) and lows of 24.6°F (-4.1°C). Weather in January »
Weather in February
The last month of the winter, February, is another cold month in O'Fallon, Illinois, with temperature in the range of an average low of 27.7°F (-2.4°C) and an average high of 42.1°F (5.6°C). The shift into February finds O'Fallon at an average high-temperature of a still wintry 42.1°F (5.6°C), closely comparable to January's conditions. Weather in February »
Weather in March
The first month of the spring, March, is a cool month in O'Fallon, Illinois, with an average temperature fluctuating between 54.5°F (12.5°C) and 37.9°F (3.3°C). A rise in the average high-temperature is observed during March, moving from a wintry 42.1°F (5.6°C) in February to a fresh 54.5°F (12.5°C). Weather in March »
Weather in April
April is an enjoyable spring month in O'Fallon, Illinois, with an average temperature fluctuating between 47.8°F (8.8°C) and 64.9°F (18.3°C). April's arrival sees a rise in the average high-temperature, jumping from March's fresh 54.5°F (12.5°C) to an enjoyable 64.9°F (18.3°C). Weather in April »
Weather in May
May, the last month of the spring in O'Fallon, is a warm month, with temperature in the range of an average high of 74.8°F (23.8°C) and an average low of 57.9°F (14.4°C). May's arrival brings a change in high-temperatures, moving from a comfortable 64.9°F (18.3°C) in April to a warm 74.8°F (23.8°C). Weather in May »
Weather in June
The first month of the summer, June, is still a warm month in O'Fallon, Illinois, with an average temperature ranging between min 66.6°F (19.2°C) and max 83.7°F (28.7°C). June brings a slight increase in the average high-temperature, progressing from a warm 74.8°F (23.8°C) in May to a still moderately hot 83.7°F (28.7°C). Weather in June »
Weather in July
July, like June, in O'Fallon, Illinois, is another warm summer month, with an average temperature varying between 85.6°F (29.8°C) and 68.2°F (20.1°C). In O'Fallon, July is identified by the highest average temperatures, reaching a peak of 85.6°F (29.8°C) and a low of 68.2°F (20.1°C). In July, the heat index is appraised at a sweltering 98.6°F (37°C). Weather in July »
Weather in August
The last month of the summer, August, is another warm month in O'Fallon, Illinois, with temperature in the range of an average high of 84.2°F (29°C) and an average low of 66°F (18.9°C). O'Fallon experiences a minor change to a still warm 84.2°F (29°C) in average high-temperature during August, closely reflecting July. Weather in August »
Weather in September
The first month of the autumn, September, is still a warm month in O'Fallon, Illinois, with temperature in the range of an average high of 79°F (26.1°C) and an average low of 60.3°F (15.7°C). O'Fallon's average high-temperature in September is a still warm 79°F (26.1°C), marking an insignificant difference from the 84.2°F (29°C) of August. Weather in September »
Weather in October
October, the same as September, is another comfortable autumn month in O'Fallon, Illinois, with temperature in the range of an average high of 66.6°F (19.2°C) and an average low of 48.7°F (9.3°C). In O'Fallon, the beginning of October is marked by a lowered average high-temperature, shifting from September's moderately hot 79°F (26.1°C) to a comfortable 66.6°F (19.2°C). Weather in October »
Weather in November
November, the last month of the autumn in O'Fallon, is another cool month, with an average temperature varying between 53.1°F (11.7°C) and 38.1°F (3.4°C). The onset of November entails a temperature shift, as the average high-temperature decreases from a comfortable 66.6°F (19.2°C) in October to a cool 53.1°F (11.7°C). Weather in November »
Weather in December
The first month of the winter, December, is also an icy month in O'Fallon, Illinois, with temperature in the range of an average low of 30.6°F (-0.8°C) and an average high of 42.6°F (5.9°C). The commencement of December indicates a shift in the average high-temperature, receding from November's fresh 53.1°F (11.7°C) to a cold 42.6°F (5.9°C). Weather in December »
Updated: Aug 8, 2024
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
What is the coldest month?
In O'Fallon, January is the month with the lowest recorded average temperatures, measuring a high of 37.8°F (3.2°C) and a low of 24.6°F (-4.1°C).
How much does it rain?
Throughout the year, there are 108.8 rainfall days, and 10.24" (260mm) of precipitation is accumulated.
When does it snow?
Months with snowfall are January through March, November and December.
What is the snowiest month?
The month with the most snowfall is January, when snow falls for 4.7 days and typically aggregates up to 0.51" (13mm) of snow.
How many days does it snow?
In O'Fallon, during the entire year, snow falls for 13.3 days and aggregates up to 1.14" (29mm) of snow.
What is the month with the least sunshine?
January has the least sunshine of the year, with an average of 4.5h of sunshine.
What is the month with the lowest UV index?
January, February, November and December, with an average maximum UV index of 2, are months with the lowest UV index.
When is Daylight Saving Time (DST)?
On Sunday, March 10. 2024, at 2:00 am, Daylight Saving Time starts, and the time zone changes from CST to CDT. Daylight Saving Time ends Sunday, November 3. 2024, at 2:00 am, and the time zone reverts from CDT to CST.
When it does not snow?
In O'Fallon, Illinois, snow does not fall in April through October.
What are the most humid months?
The months with the highest humidity are May, July and August, with an average relative humidity of 79%.
What are the months with the highest UV index?
May through August, with an average maximum UV index of 6, are months with the highest UV index.
When are the longest days?
With an average of 14h and 48min of daylight, June has the longest days of the year in O'Fallon, Illinois.
What are the months with the most sunshine?
The months with the most sunshine are June and July, with an average of 10.4h of sunshine.
What are the warmest months?
With average high temperatures of 85.6°F (29.8°C) and lows of 68.2°F (20.1°C), July is the warmest month.
What is the wettest month?
The month with the most rainfall is July, when the rain falls for 13.1 days and typically aggregates up to 1.42" (36mm) of precipitation.
What is the least humid month?
With an average relative humidity of 70%, October is the least humid month.
What is the driest month in O'Fallon?
December is the month with the least rainfall. Rain falls for 4.6 days and accumulates 0.31" (8mm) of precipitation.
What is the month with the shortest days?
The month with the shortest days is December, with an average of 9h and 30min of daylight.
Average temperature
O'Fallon, IL
The warmest month (with the highest average high temperature) is July (85.6°F).
The month with the lowest average high temperature is January (37.8°F).
The month with the highest average low temperature is July (68.2°F).
The coldest month (with the lowest average low temperature) is January (24.6°F).
Average pressure
O'Fallon, IL
- Average pressure in January:
30.16"Hg - Average pressure in February:
30.12"Hg - Average pressure in March:
30.07"Hg - Average pressure in April:
29.94"Hg - Average pressure in May:
29.96"Hg - Average pressure in June:
29.93"Hg
- Average pressure in July:
29.97"Hg - Average pressure in August:
29.98"Hg - Average pressure in September:
30.03"Hg - Average pressure in October:
30.04"Hg - Average pressure in November:
30.13"Hg - Average pressure in December:
30.13"Hg
The month with the highest atmospheric pressure is January (30.16"Hg).
The month with the lowest atmospheric pressure is June (29.93"Hg).
Average wind speed
O'Fallon, IL
- Average wind speed in January:
9.5mph - Average wind speed in February:
9.4mph - Average wind speed in March:
9.3mph - Average wind speed in April:
9.1mph - Average wind speed in May:
7.5mph - Average wind speed in June:
6.6mph
- Average wind speed in July:
5.6mph - Average wind speed in August:
5.7mph - Average wind speed in September:
6.2mph - Average wind speed in October:
8.2mph - Average wind speed in November:
8.8mph - Average wind speed in December:
8.9mph
The windiest month (with the highest average wind speed) is January (9.5mph).
The calmest month (with the lowest average wind speed) is July (5.6mph).
Average humidity
O'Fallon, IL
The months with the highest relative humidity are May, July and August (79%).
The month with the lowest relative humidity is October (70%).
Average rainfall
O'Fallon, IL
- Average rainfall in January:
0.71" - Average rainfall in February:
0.47" - Average rainfall in March:
0.71" - Average rainfall in April:
1.1" - Average rainfall in May:
1.34" - Average rainfall in June:
1.14"
- Average rainfall in July:
1.42" - Average rainfall in August:
1.26" - Average rainfall in September:
0.67" - Average rainfall in October:
0.75" - Average rainfall in November:
0.35" - Average rainfall in December:
0.31"
The wettest month (with the highest rainfall) is July (1.42").
The driest month (with the least rainfall) is December (0.31").
Average rainfall days
O'Fallon, IL
- Average rainfall days in January:
4.8 days - Average rainfall days in February:
5.3 days - Average rainfall days in March:
9.7 days - Average rainfall days in April:
12.3 days - Average rainfall days in May:
12.8 days - Average rainfall days in June:
11.1 days
- Average rainfall days in July:
13.1 days - Average rainfall days in August:
11.1 days - Average rainfall days in September:
9.8 days - Average rainfall days in October:
8.3 days - Average rainfall days in November:
5.9 days - Average rainfall days in December:
4.6 days
The month with the highest number of rainy days is July (13.1 days).
The month with the least rainy days is December (4.6 days).
Average snowfall
O'Fallon, IL
The month with the highest snowfall is January (0.51").
The months with the least snowfall are April, May, June, July, August, September and October (0").
Average snowfall days
O'Fallon, IL
- Average snowfall days in January:
4.7 days - Average snowfall days in February:
4 days - Average snowfall days in March:
1.4 days - Average snowfall days in April:
0.1 days - Average snowfall days in May:
0 days - Average snowfall days in June:
0 days
- Average snowfall days in July:
0 days - Average snowfall days in August:
0 days - Average snowfall days in September:
0 days - Average snowfall days in October:
0 days - Average snowfall days in November:
0.7 days - Average snowfall days in December:
2.4 days
The month with the highest number of snowfall days is January (4.7 days).
The months with the least snowfall days are May, June, July, August, September and October (0 days).
Average daylight / Average sunshine
O'Fallon, IL
- Average daylight in January:
9h and 5min - Average daylight in February:
10h and 5min - Average daylight in March:
12h and 0min - Average daylight in April:
13h and 1min - Average daylight in May:
14h and 2min - Average daylight in June:
14h and 5min
- Average daylight in July:
14h and 3min - Average daylight in August:
13h and 4min - Average daylight in September:
12h and 2min - Average daylight in October:
11h and 1min - Average daylight in November:
10h and 1min - Average daylight in December:
9h and 3min
The month with the longest days is June (Average daylight: 14h and 48min).
The month with the shortest days is December (Average daylight: 9h and 30min).
- Average sunshine in January:
4h and 3min - Average sunshine in February:
4h and 4min - Average sunshine in March:
6h and 2min - Average sunshine in April:
8h and 4min - Average sunshine in May:
9h and 2min - Average sunshine in June:
10h and 2min
- Average sunshine in July:
10h and 2min - Average sunshine in August:
10h and 1min - Average sunshine in September:
9h and 2min - Average sunshine in October:
6h and 2min - Average sunshine in November:
5h and 2min - Average sunshine in December:
4h and 4min
The months with the most sunshine are June and July (Average sunshine: 10h and 24min).
The month with the least sunshine is January (Average sunshine: 4h and 30min).
Average sunshine days
O'Fallon, IL
- Average sunshine days in January:
23.1 days - Average sunshine days in February:
19.6 days - Average sunshine days in March:
18.4 days - Average sunshine days in April:
15.8 days - Average sunshine days in May:
15.5 days - Average sunshine days in June:
16.2 days
- Average sunshine days in July:
15.5 days - Average sunshine days in August:
18 days - Average sunshine days in September:
18.3 days - Average sunshine days in October:
22.2 days - Average sunshine days in November:
22.5 days - Average sunshine days in December:
23.6 days
The month with the most sunshine days is December (23.6 days).
The months with the least sunshine days are May and July (15.5 days).
Average UV index
O'Fallon, IL
The months with the highest UV index are May, June, July and August (UV index 6).
The months with the lowest UV index are January, February, November and December (UV index 2).
Average cloud cover
O'Fallon, IL
The month with the most cloud cover is January (Cloud cover 51).
The month with the least cloud cover is August (Cloud cover 28).
Average visibility
O'Fallon, IL
The months with the highest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).
The months with the lowest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).
O'Fallon, Illinois, USA
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