The best times to visit O’Fallon for ideal weather are

April 16th to June 10th

based on average temperature and humidity from NOAA (the National Oceanic and Atmospheric Administration). Read below for more weather and travel details.



Other O’Fallon Travel Info

Weather in O’Fallon


Average temperatures in O’Fallon vary drastically. Considering humidity, temperatures feel nice between summer and winter. The temperatures feel cold for about half the year, and too hot for part of the year with a chance of rain or snow throughout most of the year. The area is less temperate than some — in the 21st percentile for pleasant weather — compared to tourist destinations worldwide. Weeks with ideal weather are listed above. If you’re looking for the very warmest time to visit O’Fallon, the hottest months are July, August, and then June. See average monthly temperatures below. The warmest time of year is generally mid July where highs are regularly around 90°F (32.2°C) with temperatures rarely dropping below 68.3°F (20.2°C) at night.

O’Fallon Temperatures (Fahrenheit)


O’Fallon Temperatures (Celsius)


“Feels-Like” Temperatures

The way we experience weather isn’t all about temperature. Higher temperatures affect us much more at higher humidity, and colder temperatures feel piercing with high winds. Our perceived temperatures factor in humidity and wind chill to better represent how hot or cold the day feels to a person.

O’Fallon Perceived Temperature (F)


O’Fallon Perceived Temperature (C)



Average O’Fallon Temperatures by Month

Daily highs (averaged for the month) usually give the best indication of the weather. A significantly lower mean and low generally just means it gets colder at night.

Show Fahrenheit

Month Avg. High (°F) Avg. Mean (°F) Avg. Low (°F)
Jan 40.9 30.4 21.8
Feb 42.7 32.1 23.7
Mar 59.2 46.4 36.3
Apr 69.4 56.8 45.8
May 78.3 66.5 56
Jun 86.9 75.6 65.1
Jul 89 77.6 67.2
Aug 88.7 76.6 65.9
Sep 81.7 68.6 58
Oct 70.4 57 45.8
Nov 57 45.1 35.1
Dec 44.9 35.7 28

Show Celsius

Month Avg. High (°C) Avg. Mean (°C) Avg. Low (°C)
Jan 4.9 -0.9 -5.7
Feb 5.9 0.1 -4.6
Mar 15.1 8 2.4
Apr 20.8 13.8 7.7
May 25.7 19.2 13.3
Jun 30.5 24.2 18.4
Jul 31.7 25.3 19.6
Aug 31.5 24.8 18.8
Sep 27.6 20.3 14.4
Oct 21.3 13.9 7.7
Nov 13.9 7.3 1.7
Dec 7.2 2.1 -2.2



Precipitation (Rain or Snow)

If dry weather is what you’re after, the months with the lowest chance of significant precipitation in O’Fallon are January, August, and then February. Note that we define “significant precipitation” as .1 inches or more in this section. The lowest chance of rain or snow occurs around mid January. For example, on the week of January 15th there are no days of precipitation on average. By contrast, it’s most likely to rain or snow in late April with an average of 3 days of significant precipitation the week of April 23rd.

When can you find snow in O’Fallon? Weather stations report a good amount of seasonal snow likely to be deepest around January, especially close to early January. The best time to ski (if at all) in O’Fallon is often around around December 3rd when fresh powder is deepest. Please note that a value of 0 for snow in the graph below may either mean there was no snow, or that snow is unreported.

Chance of Precipitation

The graph below shows the % chance of rainy and snowy days in O’Fallon.

Days with precipitation

Snow on the Ground

The graph below shows the average snow on the ground in O’Fallon (in).

Snow depth

Average Rain and Snow by Month

Show Inches

Month Daily Chance of Rain Average Snow Depth (in) Total Precipitation (in)
Jan 12% 4.3 2.3
Feb 16% 1.8 1.9
Mar 22% 3.2 3.9
Apr 31% 0 6.3
May 28% 0 5.4
Jun 26% 0 5.4
Jul 21% 0 4.1
Aug 16% 0 3.5
Sep 22% 0 4
Oct 18% 0 3.4
Nov 19% 2 3
Dec 22% 2.4 4.4

Show Centimeters

Month Daily Chance of Rain Average Snow Depth (cm) Total Precipitation (cm)
Jan 12 10.9 5.8
Feb 16 4.6 4.8
Mar 22 8.1 9.9
Apr 31 0 16
May 28 0 13.7
Jun 26 0 13.7
Jul 21 0 10.4
Aug 16 0 8.9
Sep 22 0 10.2
Oct 18 0 8.6
Nov 19 5.1 7.6
Dec 22 6.1 11.2


Humidity and Wind

O’Fallon has some very humid months, with other comfortably humid months. The least humid month is April (57.3% relative humidity), and the most humid month is December (73%).

Wind in O’Fallon is usually calm. The windiest month is April, followed by March and February. April’s average wind speed of around 7.7 knots (8.9 MPH or 14.3 KPH) is considered “a gentle breeze.” Maximum sustained winds (the highest speed for the day lasting more than a few moments) are at their highest in early to mid April where average top sustained speeds reach 16 knots, which is considered a moderate breeze.

Relative Humidity (%)

The graph below shows the average % humidity by month in O’Fallon.

Avg. Relative Humidity


The graph below shows wind speed (max and average) in knots.

Max Sustained Wind
Average Daily Wind

Average Wind Speeds

Show Wind Speeds

All wind speeds are in knots. 1 knot = 1.15 MPH or 1.85 KPH.

Month Avg. Wind Avg. Wind Feel Sustained High Wind High Wind Feel
Jan 7.3 Gentle breeze 13.9 Significant breeze
Feb 7.3 Gentle breeze 14.3 Significant breeze
Mar 7.4 Gentle breeze 14.5 Significant breeze
Apr 7.7 Gentle breeze 15.6 Significant breeze
May 6 Light breeze 13.7 Significant breeze
Jun 5.6 Light breeze 13.8 Significant breeze
Jul 4.2 Light breeze 10.7 Significant breeze
Aug 3.9 Barely noticeable 10.3 Gentle breeze
Sep 4 Light breeze 10.3 Significant breeze
Oct 5.7 Light breeze 12.4 Significant breeze
Nov 6.5 Light breeze 13.3 Significant breeze
Dec 6.9 Light breeze 13.4 Significant breeze

Show Relative Humidity by Month

Month Avg. Relative Humidity
Jan 62.6%
Feb 61.8%
Mar 60%
Apr 57.3%
May 65.8%
Jun 66.8%
Jul 68.2%
Aug 67.8%
Sep 68.3%
Oct 62.3%
Nov 62.4%
Dec 73%


Is it Safe to Travel to O’Fallon?

Our best data indicates this area is generally safe. As of Dec 04, 2023 there are no travel advisories or warnings for the United States; exercise normal security precautions. Check this page for any recent changes or regions to avoid: Travel Advice and Advisories. This advisory was last updated on Dec 04, 2023.


The Busiest and Least Crowded Months

The busiest month for tourism in O’Fallon, IL, US is July, followed by June and May. Prices for hotels and flights will be most expensive during these months, though you can save if you purchase well in advance. Tourists are unlikely to visit O’Fallon in January. Those willing to visit at these times will likely find it the least expensive month.

Estimated Tourism by Month


Most Popular Months to Visit

Tourists Seeking Accommodations

Tourism graph is based on Google searches for services used by tourists relative to the rest of the year. Tourism data for this area is extrapolated based on nearby areas. Displayed data is calculated relative to the peak, so a score of 50.2 in January means 50.2% of the tourists vs. July.



Overall O’Fallon Travel Experience by Season

Spring (March through May)

Humidity and temperatures combine to make this season feel moderate. Highs range from 83.6°F (28.7°C) and 47.3°F (8.5°C) with warmer temperatures in the later months. Rain is somewhat common with 7 to 9 days of significant precipitation per month. Spring is the second busiest for tourism, which makes it a good time for those looking for things to do.

Summer (June through August)

The middle-year months have very comfortable weather with high temperatures that are quite warm. These months see moderate precipitation with 5 to 8 days of precipitation per month. June – August is the busiest season for tourism in O’Fallon, so lodging and other accommodations may cost more than usual.

Fall (September through November)

Fall daily highs range from 84.2°F (29°C) and 50.4°F (10.2°C), which will feel comfortable given the humidity and wind. It rains or snows a significant amount: 6 to 7 days per month. Tourism is the slowest during these months due to the weather, so hotels may be affordably priced.

Winter (December through February)

Weather is far too cold this time of year in O’Fallon to be enjoyable for warm weather travelers. The average high during this season is between 47.3°F (8.5°C) and 40.1°F (4.5°C). On average, it rains or snows a fair amount: 4 to 7 times per month. These times of year are fairly slow with tourists.


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