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Contents
- The climate of O'Fallon
- The best time to visit O'Fallon
- The worst time to visit O'Fallon
- Spring weather in O'Fallon
- Summer weather in O'Fallon
- Autumn weather in O'Fallon
- Winter weather in O'Fallon
- 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
The climate of O'Fallon
In the cordial town of O'Fallon, Missouri, USA, the climate generally adheres to the Köppen classification of a humid subtropical one with no distinct dry spell. This climate classification indicates that the area typically experiences mild winters, hot and muggy summers, significant rainfall year-round, and occasional snowfall during winter months.
Temperatures fluctuate throughout the year, with warmer conditions prevalent from late May through to early September featuring temperatures soaring to 87.1°F (30.6°C) in July. Winter months, between late November and February, usher in a noticeable drop in temperatures, where average lows can dip down to 23.7°F (-4.6°C) in January. A remarkable aspect of O'Fallon's climate is the humidity levels. It exhibits little variation from month to month, hovering between 70 to 79% all year round, contributing to the humid conditions characteristic of this region.
Rainfall follows a similar pattern, distributed fairly evenly throughout the year, with a peak in May of 2.76" (70mm) and a minimum in December of 0.91" (23mm). Indeed, snowfall is rare except for the colder months, primarily November to February, peaking at 1.61" (41mm) in February.
Temperatures fluctuate throughout the year, with warmer conditions prevalent from late May through to early September featuring temperatures soaring to 87.1°F (30.6°C) in July. Winter months, between late November and February, usher in a noticeable drop in temperatures, where average lows can dip down to 23.7°F (-4.6°C) in January. A remarkable aspect of O'Fallon's climate is the humidity levels. It exhibits little variation from month to month, hovering between 70 to 79% all year round, contributing to the humid conditions characteristic of this region.
Rainfall follows a similar pattern, distributed fairly evenly throughout the year, with a peak in May of 2.76" (70mm) and a minimum in December of 0.91" (23mm). Indeed, snowfall is rare except for the colder months, primarily November to February, peaking at 1.61" (41mm) in February.
The best time to visit O'Fallon
Given O'Fallon's humid subtropical climate, the period from late April through to mid-October is considered most suitable for visiting. During this time, the town enjoys pleasant weather typified by warm temperatures ranging between 65.3°F (18.5°C) to 85.5°F (29.7°C) and ample sunshine, with daylight hours hovering around 13.2 hours in April and peaking at 14.9 hours in June. A highlight of this period is the typically low wind speeds, ranging from 5.5mph (8.9km/h) to 7.2mph (11.6km/h), ensuring a calm and comfortable outdoor experience.
The worst time to visit O'Fallon
Winter season in O'Fallon, beginning in late November through to February, may not be conducive for outdoor activities due to the lower temperatures typically ranging from 23.7°F (-4.6°C) to 41.9°F (5.5°C), and the higher chances of snow, particularly in the months of January and February. The daylight hours are low as well, ranging from 9.5 hours in December to 10.8 hours in February, thus leading to shorter days and fewer daylight hours for outdoor exploration.
Spring weather in O'Fallon
The spring season in O'Fallon, from March through May, greets residents and visitors with steadily rising temperatures ranging from a low of 54.1°F (12.3°C) in March to a high of 74.5°F (23.6°C) in May. Rainfall increases during this time with April and May receiving 2.48" (63mm) and 2.76" (70mm), respectively, making them the wettest months of the year. The amount of daylight also increases significantly during this period, reaching up to 14.3 hours in May, giving plenty of daylight hours to enjoy the warming temperatures.
Summer weather in O'Fallon
O'Fallon's summer months from June to August are typified by high temperatures, abundant sunshine, and moderate rainfall. Temperatures during this period range from 79.5°F (26.4°C) to 87.1°F (30.6°C). Despite these high temperatures, frequent showers are expected with rainfall measuring between 2.13" (54mm) to 2.48" (63mm) per month. However, wind speeds are at their lowest during this time of the year, averaging from 5.5mph (8.9km/h) to 6.4mph (10.3km/h), providing a respite from the heat.
Autumn weather in O'Fallon
In autumn, from September to November, O'Fallon experiences a gradual decrease in temperature and daylight hours. The average high temperature drops from 79.5°F (26.4°C) in September to 53.2°F (11.8°C) in November, while daylight decreases from 12.4 hours in September to 10.1 hours in November. Rainfall during this season is moderate, ranging from 0.98" (25mm) in November to 1.73" (44mm) in October, making it a pleasant period to experience the changing colors of the foliage.
Winter weather in O'Fallon
Winter months in O'Fallon from December through February bring frigid temperatures, sporadic snowfall, and shorter daylight hours. Average high temperatures decrease to 41.9°F (5.5°C) in December and drop to their lowest at 37.4°F (3°C) in January, while lowest temperatures can go down to 23.7°F (-4.6°C). Snowfall, though not heavy, peaks at 1.61" (41mm) in February adding to the chilly ambiance of the town. The daylight lasts for less than 10.8 hours in these months, with December having the shortest day of 9.5 hours.
Weather in January
January in O'Fallon, Missouri is characterized by a blanket of white courtesy of the snowfall and colder temperatures playing peek-a-boo. Though a smidge warmer than the anticipated starkness of winter, it poses a significant dip from the milder climes of December. Weather in January »
Weather in February
February brings a slightly more inviting atmosphere if you are willing to endure the lingering chills from January. A slightly warmer weather pattern establishes itself, as the city starts to witness the transition into the early onset of Spring. Weather in February »
Weather in March
March signals the true arrival of Spring, as overnight lows hover around 37.9°F (3.3°C). A substantial increase in temperature is evident, showing a stark contrast to its predecessor and paving the way for the warmer weather approaching in April. Weather in March »
Weather in April
April embodies Spring fully, with a bloom in temperature noticeable from 37.9°F (3.3°C) to a welcoming 47.3°F (8.5°C). The climate becomes milder and the strength of the sun's rays, as indicated by the UV index, further escalates. Weather in April »
Weather in May
The month of May escorts in a significantly warmer atmosphere, with temperatures making a considerable leap from April. As one might expect, the UV index value increases to 6, being the month with long sunlight exposure, indicating the imminent arrival of summer. Weather in May »
Weather in June
By June, summer is unmistakably in full swing, bringing with it the delight of sun-soaked days. The transition from May is notable with a climb in day and night temperatures. A definite decrease in wind speed as we move into June ensures that no gusty winds interrupt a perfect outing. Weather in June »
Weather in July
July represents the middle of summer and is, noticeably, the month with the highest day and night temperatures. As the heat peaks, days are now longer with approximately 14.6 hours of daylight. The number of sunshine hours, however, remains consistent with the previous month. Weather in July »
Weather in August
Though August shares a similar profile with July, it holds a relief with slightly lower temperatures. August could be seen as a transition phase where the intensity of the summer heat starts decelerating, ushering a slow but comfortable segue into autumn. Weather in August »
Weather in September
As we venture into September, a decline in temperature clearly signifies the arrival of the autumn season. Even though the weather cools down considerably from August, the midday sun offers a warm respite, making it pleasant for outdoor activities. Weather in September »
Weather in October
The highlight of October is the unmistakable autumn coolness, as temperatures take a significant downward plunge from its September counterpart. October, being an autumn month, enjoys a generous amount of daylight hours and adequate sunshine that adds to the crispiness of fall. Weather in October »
Weather in November
November brings O'Fallon, Missouri closer to winter, with temperatures seeing a notable drop from October. The transition from autumn to winter is most prominent this month, preparing everyone for the chilling December ahead. It stands out with the lowest recorded rainfall measuring 0.98" (25mm), which marks it as the driest month of the year. Weather in November »
Weather in December
December declares the onset of winter as O'Fallon, Missouri grapples with a sharp decline in temperature compared to November. The shortened daylight hours and reduced sunshine hours cast a wintry ambiance over the city. Rainfall maintains a low figure at 0.91" (23mm) with only 7 rainy days recorded on average in the month. Weather in December »
Updated: Aug 14, 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 are the coldest months?
The coldest time of the year is January, with temperatures averaging a high of 37.4°F (3°C) and a low of 23.7°F (-4.6°C).
How much does it rain?
Throughout the year, there are 132.3 rainfall days, and 21.06" (535mm) of precipitation is accumulated.
When does it snow?
Months with snowfall are January through March, November and December.
How many days does it snow?
In O'Fallon, during the entire year, snow falls for 19 days and aggregates up to 4.13" (105mm) of snow.
What are the months with the least sunshine?
The months with the least sunshine are January and February, with an average of 4.7h of sunshine.
What are the months with the lowest UV index?
The months with the lowest UV index are January, February, November and December, with an average maximum UV index of 2.
What is the snowiest month in O'Fallon?
February is the month with the most snowfall. Snow falls for 5.8 days and accumulates 1.61" (41mm) of snow.
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?
April through October are months without snowfall.
What is the most humid month?
The most humid month is May, with an average relative humidity of 79%.
What is the rainiest month?
The month with the most rainfall is May, when the rain falls for 15.7 days and typically aggregates up to 2.76" (70mm) of precipitation.
When is 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?
June has the longest days of the year in O'Fallon, with an average of 14h and 48min of daylight.
What month has the most sunshine?
With an average of 10.5h of sunshine, June has the most sunshine of the year.
What is the hottest time of year?
July proves to be the warmest month, recording an average peak temperature of 87.1°F (30.6°C) and a minimum temperature of 68.5°F (20.3°C).
What is the least humid month?
The least humid month in O'Fallon is October, with an average relative humidity of 70%.
What is the driest month?
The month with the least rainfall is December, when the rain falls for 7 days and typically collects 0.91" (23mm) of precipitation.
What is the month with the shortest days?
With an average of 9h and 30min of daylight, December has the shortest days of the year.
Average temperature
O'Fallon, MO
The warmest month (with the highest average high temperature) is July (87.1°F).
The month with the lowest average high temperature is January (37.4°F).
The month with the highest average low temperature is July (68.5°F).
The coldest month (with the lowest average low temperature) is January (23.7°F).
Average pressure
O'Fallon, MO
- 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:
29.93"Hg - Average pressure in May:
29.95"Hg - Average pressure in June:
29.92"Hg
- Average pressure in July:
29.97"Hg - Average pressure in August:
29.97"Hg - Average pressure in September:
30.02"Hg - Average pressure in October:
30.03"Hg - Average pressure in November:
30.12"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 (29.92"Hg).
Average wind speed
O'Fallon, MO
- Average wind speed in January:
9.1mph - Average wind speed in February:
9mph - Average wind speed in March:
8.8mph - Average wind speed in April:
8.9mph - Average wind speed in May:
7.2mph - Average wind speed in June:
6.4mph
- Average wind speed in July:
5.5mph - Average wind speed in August:
5.6mph - Average wind speed in September:
6.1mph - Average wind speed in October:
7.8mph - Average wind speed in November:
8.5mph - Average wind speed in December:
8.6mph
The windiest month (with the highest average wind speed) is January (9.1mph).
The calmest month (with the lowest average wind speed) is July (5.5mph).
Average humidity
O'Fallon, MO
The month with the highest relative humidity is May (79%).
The month with the lowest relative humidity is October (70%).
Average rainfall
O'Fallon, MO
- Average rainfall in January:
1.14" - Average rainfall in February:
1.06" - Average rainfall in March:
1.5" - Average rainfall in April:
2.48" - Average rainfall in May:
2.76" - Average rainfall in June:
2.13"
- Average rainfall in July:
2.48" - Average rainfall in August:
2.48" - Average rainfall in September:
1.42" - Average rainfall in October:
1.73" - Average rainfall in November:
0.98" - Average rainfall in December:
0.91"
The wettest month (with the highest rainfall) is May (2.76").
The driest month (with the least rainfall) is December (0.91").
Average rainfall days
O'Fallon, MO
- Average rainfall days in January:
7.2 days - Average rainfall days in February:
6.8 days - Average rainfall days in March:
11.8 days - Average rainfall days in April:
13.3 days - Average rainfall days in May:
15.7 days - Average rainfall days in June:
14.4 days
- Average rainfall days in July:
15.2 days - Average rainfall days in August:
12.8 days - Average rainfall days in September:
11.3 days - Average rainfall days in October:
9.8 days - Average rainfall days in November:
7 days - Average rainfall days in December:
7 days
The month with the highest number of rainy days is May (15.7 days).
The month with the least rainy days is February (6.8 days).
Average snowfall
O'Fallon, MO
The month with the highest snowfall is February (1.61").
The months with the least snowfall are April, May, June, July, August, September and October (0").
Average snowfall days
O'Fallon, MO
- Average snowfall days in January:
5.8 days - Average snowfall days in February:
5.8 days - Average snowfall days in March:
1.9 days - Average snowfall days in April:
0.3 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:
1.3 days - Average snowfall days in December:
3.9 days
The months with the highest number of snowfall days are January and February (5.8 days).
The months with the least snowfall days are May, June, July, August, September and October (0 days).
Average daylight / Average sunshine
O'Fallon, MO
- 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 4min - 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 4min - Average sunshine in February:
4h and 4min - Average sunshine in March:
6h and 4min - Average sunshine in April:
8h and 4min - Average sunshine in May:
9h and 4min - Average sunshine in June:
10h and 3min
- Average sunshine in July:
10h and 2min - Average sunshine in August:
10h and 1min - Average sunshine in September:
9h and 3min - Average sunshine in October:
6h and 1min - Average sunshine in November:
5h and 2min - Average sunshine in December:
4h and 5min
The month with the most sunshine is June (Average sunshine: 10h and 30min).
The months with the least sunshine are January and February (Average sunshine: 4h and 42min).
Average sunshine days
O'Fallon, MO
- Average sunshine days in January:
20.4 days - Average sunshine days in February:
15.8 days - Average sunshine days in March:
16.1 days - Average sunshine days in April:
14.9 days - Average sunshine days in May:
12.9 days - Average sunshine days in June:
13 days
- Average sunshine days in July:
12.6 days - Average sunshine days in August:
14.7 days - Average sunshine days in September:
16.7 days - Average sunshine days in October:
20.1 days - Average sunshine days in November:
20.5 days - Average sunshine days in December:
20.6 days
The month with the most sunshine days is December (20.6 days).
The month with the least sunshine days is July (12.6 days).
Average UV index
O'Fallon, MO
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, MO
The month with the most cloud cover is January (Cloud cover 50).
The months with the least cloud cover are June, July, August and September (Cloud cover 28).
Average visibility
O'Fallon, MO
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, Missouri, USA
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