September weather forecast and climate
Decatur, IL

Weather in September

The first month of the autumn, September, is also a moderately hot month in Decatur, Illinois, with average temperature varying between 77°F (25°C) and 58.5°F (14.7°C).

Temperature

In September, the average high-temperature is essentially the same as in August - a still warm 77°F (25°C). The average low-temperature, in September, is 58.5°F (14.7°C).

Humidity

The average relative humidity in September is 76%.

Rainfall

In September, in Decatur, the rain falls for 10.6 days. Throughout September, 1.18" (30mm) of precipitation is accumulated. In Decatur, Illinois, during the entire year, the rain falls for 130.2 days and collects up to 16.34" (415mm) of precipitation.

Snowfall

In Decatur snow does not fall in May through October.

Daylight

In Decatur, the average length of the day in September is 12.4h.

Sunshine

The average sunshine in September is 9.2h.

UV index

In September, the average daily maximum UV index in Decatur, Illinois, is 5. A UV Index reading of 3 to 5 represents a moderate health risk from unsafe exposure to the UV radiation for average individuals.
Note: The average daily UV index of 5 in September transform into the following instructions:
Take precautions. Light skin individuals may get burned in less than 30 minutes. The solar radiation is most powerful near the mid-day, so the exposure to the direct Sun should be reduced accordingly. On bright days sunglasses that block both UVA and UVB rays should be worn. A hat with a wide brim is extremely helpful, as it can prevent roughly 50% of UV radiation from reaching the eyes.
[Resources]

FAQ

What is the average humidity in September in Decatur?

In September, the average relative humidity in Decatur is 76%.

How many days does it rain in September in Decatur?

In Decatur, during September, the rain falls for 10.6 days and regularly aggregates up to 1.18" (30mm) of precipitation.

When it does not snow in Decatur?

May through October are months without snowfall in Decatur, Illinois.

What is the average length of the day in September in Decatur?

In September, the average length of the day is 12.4h.

How many hours of sunshine does Decatur have in September?

In Decatur, the average sunshine in September is 9.2h.

What is the UV index intensity in September in Decatur?

In September, the average daily maximum UV index is 5. A UV Index value of 3 to 5 symbolizes a moderate health threat from unprotected exposure to the UV radiation.

Average temperature in September
Decatur, IL

Average temperature in September - Decatur, IL
  • Average high temperature in September: 77°F

The warmest month (with the highest average high temperature) is July (82°F).
The month with the lowest average high temperature is January (32.9°F).

  • Average low temperature in September: 58.5°F

The month with the highest average low temperature is July (65.7°F).
The coldest month (with the lowest average low temperature) is January (21.2°F).

[Resources]

Average pressure in September
Decatur, IL

Average pressure in September - Decatur, IL
  • Average pressure in September: 30.03"

The month with the highest atmospheric pressure is January (30.15").
The month with the lowest atmospheric pressure is June (29.92").

[Resources]

Average wind speed in September
Decatur, IL

Average wind speed in September - Decatur, IL
  • Average wind speed in September: 7.2mph

The windiest month (with the highest average wind speed) is January (10.7mph).
The calmest months (with the lowest average wind speed) are July and August (6.3mph).

[Resources]

Average humidity in September
Decatur, IL

Average humidity in September - Decatur, IL
  • Average humidity in September: 76%

The month with the highest relative humidity is July (84%).
The month with the lowest relative humidity is October (70%).

[Resources]

Average rainfall in September
Decatur, IL

Average rainfall in September - Decatur, IL
  • Average rainfall in September: 1.18"

The wettest month (with the highest rainfall) is May (2.01").
The driest months (with the least rainfall) are February and December (0.87").

[Resources]

Average rainfall days in September
Decatur, IL

Average rainfall days in September - Decatur, IL
  • Average rainfall days in September: 10.6 days

The month with the highest number of rainy days is May (17 days).
The month with the least rainy days is February (5.8 days).

[Resources]

Average snowfall in September
Decatur, IL

Average snowfall in September - Decatur, IL
  • Average snowfall in September: 0"

The month with the highest snowfall is January (1.85").
Months with the least snowfall are May, June, July, August, September and October (0").

[Resources]

Average snowfall days in September
Decatur, IL

Average snowfall days in September - Decatur, IL
  • Average snowfall days in September: 0 days

The month with the highest number of snowfall days is January (7.2 days).
Months with the least snowfall days are May, June, July, August, September and October (0 days).

[Resources]

Average daylight in September /
Average sunshine in September
Decatur, IL

Average daylight in September / Average sunshine in September - Decatur, IL
  • Average daylight in September: 12.4h

The month with the longest days is June (Average daylight: 15h).
The month with the shortest days is December (Average daylight: 9.4h).

  • Average sunshine in September: 9.2h

The month with the most sunshine is June (Average sunshine: 10.4h).
The month with the least sunshine is January (Average sunshine: 4.1h).

[Resources]

Average sunshine days in September
Decatur, IL

Average sunshine days in September - Decatur, IL
  • Average sunshine days in September: 17.3 days

The month with the most sunshine days is October (19.8 days).
The month with the least sunshine days is May (11.5 days).

[Resources]

Average UV index in September
Decatur, IL

Average UV index in September - Decatur, IL
  • Average UV index in September: 5

Months with the highest UV index are June, July and August (UV index 6).
Months with the lowest UV index are January, February, November and December (UV index 2).

[Resources]

Average cloud cover in September
Decatur, IL

Average cloud cover in September - Decatur, IL
  • Average cloud cover in September: 29

The month with the most cloud cover is January (Cloud cover 56).
The month with the least cloud cover is September (Cloud cover 29).

[Resources]

Average visibility in September
Decatur, IL

Average visibility in September - Decatur, IL
  • Average visibility in September: 6mi

Months with the highest visibility are January, February, March, April, May, June, September, October, November and December (6mi).
Months with the lowest visibility are July and August (5mi).

[Resources]

Weather forecast for your location

1. Click Locate me button
2. Allow the app to use your location
* you will be automatically redirected to the weather forecast for your location