Temperatures in September
It's warm in September in Illinois with an average temperature of 27°C. Temperatures this month range from a low of 23°C to a high of 30°C. At night, you can expect temperatures between 12°C and 19°C.
Max and Min Temperatures per Day
This chart shows the daily maximum and minimum temperatures in degrees Celsius for Illinois in September. The red line indicates the max temperatures, and the blue line shows the minimums.
Start of September
The month of September starts in Illinois with hot temperatures, averaging around 28°C during the day and nights close to 18°C. You can expect regular precipitation, but there’s also a chance for some sunny days in the first days of the month.
Since temperatures can differ between day and night, it’s a good idea to dress in layers.
Mid-September
By mid-September, the average daytime temperature stays the same at 28°C, with nights close to 16°C. There might be a few showers during this period, but plenty of dry days with sunshine too.
Temperatures vary between day and night, so it’s smart to wear layers.
End of September
By the end of September, the average daytime temperature in Illinois will be around 26°C, with nights close to 15°C. A shower might show up, but overall the weather will be dry and sunny.
As it gets cooler in the evening, it’s best to wear layers.
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Precipitation in September
In September, there is an average of 82 mm of precipitation, spread over 7 days. The wind speed is around 4 Bft, mostly coming from the South.
The average precipitation chance is 22% per day this month. Though that seems low, there are also a few days with a higher chance of precipitation.
Precipitation Chance
This chart shows the daily precipitation chance (in percentages) in September for Illinois. 0% means it never rained on that day in the past 10 years, and 100% means it rained every day. All values in between represent the average chance of precipitation on that day.
Illinois in September |
UK | ||
|---|---|---|---|
 Average Temperature |
27°C | 20°C | |
 High Temp |
30°C | 22°C | |
| Low Temp |
23°C | 17°C | |
 Total Precipitation |
82 mm | 44 mm | |
| Rainy Days |
7 days | 8 days | |
August
UV index
The UV index is a maximum of 5 this month. That's a moderate value on the intensity scale of 1 to 11. Unprotected skin can burn in about 30 minutes.
Is September a good time to visit Illinois?
Want nice weather? Then September is a great time to be in Illinois. You’ll have pleasant temperatures and not too much rain this month.
Temperature records for Illinois in September
With 36°C, Illinois hit the highest temperature in the last 10 years in September 2015. The lowest daytime temperature in this month was 12°C in 2014. The extreme night temperatures ranged from a low of 4°C to a high of 24°C.
Check out the climate of Illinois for all months and discover the best travel time
The climate of Illinois is based on weather data from . Other spots, like New York City, Miami or Los Angeles, might have different weather. You can check out all destinations in Illinois for a full picture of the climate.
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Daily Temperature in September in Illinois
This chart shows the average daily temperatures, both day and night, for each day in September in Illinois, measured in degrees Celsius. The red line represents the maximum temperatures, while the blue line shows the minimums. The days of the month are displayed at the bottom of the chart. The data, based on historical observations, gives an overview of the average daily temperatures during this month.
Daily Precipitation in September in Illinois
The chart below shows the average daily precipitation in September for Illinois, measured in millimetres over the past years. Precipitation is always measured as water, even if it’s snow or hail. The days of the month are shown at the bottom of the chart.
A low average precipitation means that the chance of rain on that day is usually small, while a higher average suggests that rain is more likely. But it’s still an average, so each day can be different. Based on historical weather data for September, you can expect around 7 days of rain in Illinois.
Daily UV Index in September in Illinois
This chart shows the average daily UV index in September in Illinois, with the UV index ranging from 0 to a maximum of 11. The bottom of the chart shows the days of the month. Based on historical data, this chart provides an idea of the daily UV radiation levels you can expect.
Temperature in September in Illinois Over the Years
This chart shows the average temperature in September in Illinois, measured in degrees Celsius, over the past years.
Total Precipitation in September in Illinois Over the Years
This chart shows the average precipitation in September in Illinois, measured in millimetres over the past years. Precipitation is always measured as water, even if it’s snow or hail.
Daily climate in September for Illinois
Click on a specific day in September for detailed info on the typical weather on that day in Illinois. Check out the historical temperatures and precipitation over the past 10 years on this day.
Weather experiences in September in Illinois
Have you been to Illinois in September?
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Average Weather in Illinois by Month
Click on a month below to see detailed weather info for Illinois. Based on historical weather data, you can see the average temperature, precipitation, wind, and UV index for each day of the month.
