The best times to visit Southwest Illinois for ideal weather are
April 16th to June 17th
September 3rd to October 28th
based on average temperature and humidity from NOAA (the National Oceanic and Atmospheric Administration). Read below for more weather and travel details.
Southwest Illinois Travel Guide
Other Southwest Illinois Travel Info
Weather in Southwest Illinois
Average temperatures in Southwest Illinois 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 very low chance of rain or snow throughout the year. The area is somewhat temperate — in the 49th 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 Southwest Illinois, the hottest months are July, August, and then June. See average monthly temperatures below. The warmest time of year is generally mid June where highs are regularly around 88.5°F (31.4°C) with temperatures rarely dropping below 69.4°F (20.8°C) at night.
Southwest Illinois Temperatures (Fahrenheit)
Southwest Illinois Temperatures (Celsius)
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.
Southwest Illinois Perceived Temperature (F)
Southwest Illinois Perceived Temperature (C)
Average Southwest Illinois 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.
|Month||Avg. High (°F)||Avg. Mean (°F)||Avg. Low (°F)|
|Month||Avg. High (°C)||Avg. Mean (°C)||Avg. Low (°C)|
Precipitation (Rain or Snow)
If dry weather is what you’re after, the months with the lowest chance of significant precipitation in Southwest Illinois are February, September, and then January. 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 early to mid May with an average of 1 days of significant precipitation the week of May 7th.
When can you find snow in Southwest Illinois? Weather stations report no annual snow. 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 Southwest Illinois.
Snow on the Ground
The graph below shows the average snow on the ground in Southwest Illinois (in).
Average Rain and Snow by Month
|Month||Daily Chance of Rain||Average Snow Depth (in)||Total Precipitation (in)|
|Month||Daily Chance of Rain||Average Snow Depth (cm)||Total Precipitation (cm)|
Humidity and Wind
Southwest Illinois has some high humidity months, with other comfortably humid months. The least humid month is April (56.8% relative humidity), and the most humid month is December (69.5%).
Wind in Southwest Illinois is usually calm. The windiest month is April, followed by March and January. April’s average wind speed of around 7.1 knots (8.1 MPH or 13.1 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 April where average top sustained speeds reach 15.1 knots, which is considered a moderate breeze.
Relative Humidity (%)
The graph below shows the average % humidity by month in Southwest Illinois.
The graph below shows wind speed (max and average) in knots.
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||6.7||Light breeze||13.4||Significant breeze|
|Feb||6.5||Light breeze||13.4||Significant breeze|
|Mar||7||Gentle breeze||14.1||Significant breeze|
|Apr||7.1||Gentle breeze||14.6||Significant breeze|
|May||5.4||Light breeze||12.5||Significant breeze|
|Jun||5||Light breeze||12.2||Significant breeze|
|Jul||3.9||Barely noticeable||10.2||Significant breeze|
|Aug||3.5||Barely noticeable||9.6||Gentle breeze|
|Sep||3.7||Barely noticeable||9.7||Significant breeze|
|Oct||5.2||Light breeze||11.7||Significant breeze|
|Nov||6||Light breeze||12.3||Significant breeze|
|Dec||6.4||Light breeze||12.9||Significant breeze|
Show Relative Humidity by Month
|Month||Avg. Relative Humidity|
Is it Safe to Travel to Southwest Illinois?
Our best data indicates this area is generally safe. As of Oct 07, 2019 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 Sep 23, 2019.
The Busiest and Least Crowded Months
The busiest month for tourism in Southwest Illinois, 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 Southwest Illinois 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
Overall Southwest Illinois Travel Experience by Season
Spring (March through May)
Humidity and temperatures combine to make this season feel moderate. Highs range from 82.4°F (28°C) and 47.3°F (8.5°C) with warmer temperatures in the later months. Rain is rare with 1 to 2 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 1 to 2 days of precipitation per month. June – August is the busiest season for tourism in Southwest Illinois, so lodging and other accommodations may cost more than usual.
Fall (September through November)
Fall daily highs range from 83.4°F (28.6°C) and 49.9°F (9.9°C), which will feel comfortable given the humidity and wind. It rains or snows a normal amount: 1 to 2 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 Southwest Illinois to be enjoyable for warm weather travelers. The average high during this season is between 47.3°F (8.5°C) and 40.2°F (4.6°C). On average, it rains or snows a smalll amount: 1 to 2 times per month. These times of year are fairly slow with tourists.