Contents
- Weather in September
- Frequently asked questions
- Average temperature in September
- Average pressure in September
- Average wind speed in September
- Average humidity in September
- Average rainfall in September
- Average rainfall days in September
- Average snowfall in September
- Average snowfall days in September
- Average daylight in September
- Average sunshine in September
- Average sunshine days in September
- Average UV index in September
- Average cloud cover in September
- Average visibility in September
Weather in September
Temperature
The onset of September entails a subtle temperature shift, as the average high-temperature eases from a warm 84°F (28.9°C) in August to a still moderately hot 78.6°F (25.9°C). Alton encounters an average low-temperature of 59.5°F (15.3°C) during September nights.Humidity
In September, the average relative humidity in Alton is 74%.Rainfall
In Alton, in September, it is raining for 10.5 days, with typically 1.3" (33mm) of accumulated precipitation. Throughout the year, there are 128.3 rainfall days, and 18.9" (480mm) of precipitation is accumulated.Snowfall
In Alton, Illinois, snow does not fall in April through October.Daylight
In September, the average length of the day is 12h and 26min.On the first day of September, sunrise is at 6:30 am and sunset at 7:30 pm. On the last day of the month, sunrise is at 6:56 am and sunset at 6:44 pm CDT.
Sunshine
In September, the average sunshine in Alton is 9.3h.UV index
The average daily maximum UV index in September in Alton is 5. A UV Index estimate of 3 to 5 represents a moderate health risk from unsafe exposure to UV radiation for the average person.Note: An average maximum UV index of 5 in September leads to these recommendations:
Be vigilant - Suggestions to stave off sun damage are provided. Direct exposure to the Sun's intense radiation around midday should be avoided for health reasons. 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.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
What is the average September temperature in Alton?
What is the average humidity in September in Alton?
How much does it rain in Alton in September?
When it does not snow in Alton?
What is the average length of the day in September in Alton?
When is the sunrise / sunset in September in Alton?
How long on average sun shines in September in Alton?
What is the UV index intensity in September in Alton?
Average temperature in September
Alton, IL
- Average high temperature in September: 78.6°F
The warmest month (with the highest average high temperature) is July (85.3°F).
The month with the lowest average high temperature is January (36.1°F).
- Average low temperature in September: 59.5°F
The month with the highest average low temperature is July (67.6°F).
The coldest month (with the lowest average low temperature) is January (23.2°F).
Average pressure in September
Alton, IL
- Average pressure in September: 30.02"Hg
The month with the highest atmospheric pressure is January (30.16"Hg).
The month with the lowest atmospheric pressure is June (29.92"Hg).
Average wind speed in September
Alton, IL
- Average wind speed in September: 6.3mph
The windiest month (with the highest average wind speed) is January (9.6mph).
The calmest month (with the lowest average wind speed) is July (5.7mph).
Average humidity in September
Alton, IL
- Average humidity in September: 74%
The month with the highest relative humidity is July (80%).
The month with the lowest relative humidity is October (71%).
Average rainfall in September
Alton, IL
- Average rainfall in September: 1.3"
The wettest month (with the highest rainfall) is May (2.44").
The driest month (with the least rainfall) is February (0.83").
Average rainfall days in September
Alton, IL
- Average rainfall days in September: 10.5 days
The month with the highest number of rainy days is July (15.4 days).
The month with the least rainy days is January (5.7 days).
Average snowfall in September
Alton, IL
- Average snowfall in September: 0"
The month with the highest snowfall is February (1.14").
The months with the least snowfall are April, May, June, July, August, September and October (0").
Average snowfall days in September
Alton, IL
- Average snowfall days in September: 0 days
The month with the highest number of snowfall days is January (5.4 days).
The months with the least snowfall days are May, June, July, August and September (0 days).
Average daylight in September /
Average sunshine in September
Alton, IL
- Average daylight in September: 12h and 2min
The month with the longest days is June (Average daylight: 14h and 54min).
The month with the shortest days is December (Average daylight: 9h and 30min).
- Average sunshine in September: 9h and 2min
The month with the most sunshine is June (Average sunshine: 10h and 24min).
The months with the least sunshine are January and February (Average sunshine: 4h and 30min).
Average sunshine days in September
Alton, IL
- Average sunshine days in September: 17.5 days
The month with the most sunshine days is December (21 days).
The month with the least sunshine days is June (12.6 days).
Average UV index in September
Alton, IL
- Average UV index in September: 5
The months with the highest UV index are June, July and August (UV index 6).
The months with the lowest UV index are January, February, November and December (UV index 2).
Average cloud cover in September
Alton, IL
- Average cloud cover in September: 29
The month with the most cloud cover is January (Cloud cover 52).
The month with the least cloud cover is August (Cloud cover 28).
Average visibility in September
Alton, IL
- Average visibility in September: 6mi
The months with the highest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).
The months with the lowest visibility are January, February, March, April, May, June, July, August, September, October, November and December (6mi).
Alton, Illinois, USA
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