The best times to visit Southeast Illinois for ideal weather are
April 16th to June 10th
or
September 3rd to October 14th
based on average temperature and humidity from NOAA (the National Oceanic and Atmospheric Administration). Read below for more weather and travel details.
Southeast Illinois Travel Guide
Other Southeast Illinois Travel Info
Weather in Southeast Illinois
Temperature
Average temperatures in Southeast Illinois vary drastically. Considering humidity, temperatures feel cold for about half of the year and otherwise nice with a very low chance of rain or snow throughout the year. The area is somewhat temperate — in the 50th 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 Southeast Illinois, the hottest months are July, June, and then August. See average monthly temperatures below. The warmest time of year is generally mid June where highs are regularly around 88.1°F (31.2°C) with temperatures rarely dropping below 69.3°F (20.7°C) at night.
Southeast Illinois Temperatures (Fahrenheit)
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Southeast Illinois Temperatures (Celsius)
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“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.
Southeast Illinois Perceived Temperature (F)
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Southeast Illinois Perceived Temperature (C)
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Average Southeast 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.
Show Fahrenheit
| Month | Avg. High (°F) | Avg. Mean (°F) | Avg. Low (°F) |
|---|---|---|---|
| Jan | 39.8 | 30.9 | 23.5 |
| Feb | 42.1 | 32.7 | 25.4 |
| Mar | 57.3 | 46.5 | 38 |
| Apr | 68.2 | 57.1 | 47.6 |
| May | 77.6 | 66.9 | 57.6 |
| Jun | 86 | 75.7 | 66.2 |
| Jul | 87.1 | 76.8 | 67.6 |
| Aug | 86.8 | 75.6 | 65.8 |
| Sep | 81.4 | 69.4 | 59.5 |
| Oct | 69.9 | 57.7 | 47.5 |
| Nov | 56.3 | 45.6 | 36.6 |
| Dec | 45.3 | 36.8 | 30.1 |
Show Celsius
| Month | Avg. High (°C) | Avg. Mean (°C) | Avg. Low (°C) |
|---|---|---|---|
| Jan | 4.3 | -0.6 | -4.7 |
| Feb | 5.6 | 0.4 | -3.7 |
| Mar | 14.1 | 8.1 | 3.3 |
| Apr | 20.1 | 13.9 | 8.7 |
| May | 25.3 | 19.4 | 14.2 |
| Jun | 30 | 24.3 | 19 |
| Jul | 30.6 | 24.9 | 19.8 |
| Aug | 30.4 | 24.2 | 18.8 |
| Sep | 27.4 | 20.8 | 15.3 |
| Oct | 21.1 | 14.3 | 8.6 |
| Nov | 13.5 | 7.6 | 2.6 |
| Dec | 7.4 | 2.7 | -1.1 |
Precipitation (Rain or Snow)
If dry weather is what you’re after, the months with the lowest chance of significant precipitation in Southeast Illinois are January, February, and then April. Note that we define “significant precipitation” as .1 inches or more in this section. The lowest chance of rain or snow occurs around early January. For example, on the week of January 1st there are no days of precipitation on average. By contrast, it’s most likely to rain or snow in mid June with an average of 0 days of significant precipitation the week of June 18th.
When can you find snow in Southeast 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 Southeast Illinois.
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Snow on the Ground
The graph below shows the average snow on the ground in Southeast Illinois (in).
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Average Rain and Snow by Month
Show Inches
| Month | Daily Chance of Rain | Average Snow Depth (in) | Total Precipitation (in) |
|---|---|---|---|
| Jan | 0% | 0 | 0 |
| Feb | 0% | 0 | 0 |
| Mar | 4% | 0 | 0.8 |
| Apr | 0% | 0 | 0 |
| May | 0% | 0 | 0 |
| Jun | 2% | 0 | 0.1 |
| Jul | 0% | 0 | 0 |
| Aug | 0% | 0 | 0 |
| Sep | 0% | 0 | 0 |
| Oct | 2% | 0 | 0.2 |
| Nov | 1% | 0 | 0.1 |
| Dec | 1% | 0 | 0.1 |
Show Centimeters
| Month | Daily Chance of Rain | Average Snow Depth (cm) | Total Precipitation (cm) |
|---|---|---|---|
| Jan | 0 | 0 | 0 |
| Feb | 0 | 0 | 0 |
| Mar | 4 | 0 | 2 |
| Apr | 0 | 0 | 0 |
| May | 0 | 0 | 0 |
| Jun | 2 | 0 | 0.3 |
| Jul | 0 | 0 | 0 |
| Aug | 0 | 0 | 0 |
| Sep | 0 | 0 | 0 |
| Oct | 2 | 0 | 0.5 |
| Nov | 1 | 0 | 0.3 |
| Dec | 1 | 0 | 0.3 |
Humidity and Wind
Southeast Illinois has some very humid months, with other comfortably humid months. The least humid month is April (55.1% relative humidity), and the most humid month is December (72.4%).
Wind in Southeast Illinois is usually calm. The windiest month is March, followed by April and February. March’s average wind speed of around 6.2 knots (7.1 MPH or 11.4 KPH) is considered “a light 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 14.8 knots, which is considered a moderate breeze.
Relative Humidity (%)
The graph below shows the average % humidity by month in Southeast Illinois.
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Wind
The graph below shows wind speed (max and average) in knots.
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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 | 5.6 | Light breeze | 12 | Significant breeze |
| Feb | 5.7 | Light breeze | 12.4 | Significant breeze |
| Mar | 6.2 | Light breeze | 13.3 | Significant breeze |
| Apr | 6 | Light breeze | 14 | Significant breeze |
| May | 4.9 | Light breeze | 12.2 | Significant breeze |
| Jun | 4.1 | Light breeze | 11.4 | Significant breeze |
| Jul | 3.3 | Barely noticeable | 9.7 | Significant breeze |
| Aug | 2.9 | Barely noticeable | 9.2 | Gentle breeze |
| Sep | 3.5 | Barely noticeable | 9.7 | Significant breeze |
| Oct | 4.5 | Light breeze | 11 | Significant breeze |
| Nov | 5 | Light breeze | 11.8 | Significant breeze |
| Dec | 5.2 | Light breeze | 11.5 | Significant breeze |
Show Relative Humidity by Month
| Month | Avg. Relative Humidity |
|---|---|
| Jan | 64% |
| Feb | 59.9% |
| Mar | 58.5% |
| Apr | 55.1% |
| May | 62.2% |
| Jun | 63.8% |
| Jul | 67.8% |
| Aug | 66.5% |
| Sep | 61.9% |
| Oct | 56% |
| Nov | 60.1% |
| Dec | 72.4% |
Is it Safe to Travel to Southeast Illinois?
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 Southeast Illinois, the United States 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 Southeast 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
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Overall Southeast Illinois Travel Experience by Season
Spring (March through May)
Humidity and temperatures combine to make this season feel moderate. Highs range from 82.6°F (28.1°C) and 45.7°F (7.6°C) with warmer temperatures in the later months. Rain is extremely rare with 0 to 1 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 about 0 days of precipitation per month. June – August is the busiest season for tourism in Southeast Illinois, so lodging and other accommodations may cost more than usual.
Fall (September through November)
Fall daily highs range from 83.5°F (28.6°C) and 49.8°F (9.9°C), which will feel comfortable given the humidity and wind. It rains or snows a barely noticeable amount: 0 to 1 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 Southeast Illinois to be enjoyable for warm weather travelers. The average high during this season is between 45.7°F (7.6°C) and 38.8°F (3.8°C). On average, it rains or snows a insignificant amount: consistently 0 times per month. These times of year are fairly slow with tourists.
Best Times to Travel› the United States › Southeast Illinois, the United States