September weather forecastO'Fallon, MO
September
Weather in September
As we venture into September, a decline in temperature clearly signifies the arrival of the autumn season. Even though the weather cools down considerably from August, the midday sun offers a warm respite, making it pleasant for outdoor activities. This month sees a reduction in rainfall amounting to 1.42" (36mm), bringing drier days than the wet August. The UV index drops to 5, which means sunshine is less harsh but protective measures are still recommended. It also rings the last bell for snow-free period before the arrival of the late autumn chill.Temperature
As September arrives, O'Fallon's weather displays a minor decrease in high-temperatures, transitioning from August's warm 85.5°F (29.7°C) to a still moderately hot 79.5°F (26.4°C). O'Fallon usually reports an average low-temperature of 60.1°F (15.6°C) during the month of September.Humidity
In O'Fallon, the average relative humidity in September is 73%.Rainfall
In O'Fallon, in September, during 11.3 rainfall days, 1.42" (36mm) of precipitation is typically accumulated. In O'Fallon, Missouri, during the entire year, the rain falls for 132.3 days and collects up to 21.06" (535mm) of precipitation.Snowfall
In O'Fallon, snow does not fall in April through October.Daylight
In O'Fallon, the average length of the day in September is 12h and 26min.On the first day of the month, sunrise is at 6:32 am and sunset at 7:32 pm. On the last day of September, sunrise is at 6:58 am and sunset at 6:46 pm CDT.
Sunshine
In September, the average sunshine is 9.5h.UV index
The average daily maximum UV index in September is 5. A UV Index reading of 3 to 5 represents a medium health hazard from exposure to the Sun's UV radiation for average individuals.Note: In September, the maximum UV index of 5 suggests this advice:
Be mindful. Individuals with a lighter skin tone may suffer burns in less than 30 minutes. Minimize direct exposure to the Sun during midday when its radiation is at its peak. Clothes that are both tight-knit and comfortably loose are prime choices for sun protection.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
Average temperature in September
O'Fallon, MO
- Average high temperature in September: 79.5°F
The warmest month (with the highest average high temperature) is July (87.1°F).
The month with the lowest average high temperature is January (37.4°F).
- Average low temperature in September: 60.1°F
The month with the highest average low temperature is July (68.5°F).
The coldest month (with the lowest average low temperature) is January (23.7°F).
Average pressure in September
O'Fallon, MO
- 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
O'Fallon, MO
- Average wind speed in September: 6.1mph
The windiest month (with the highest average wind speed) is January (9.1mph).
The calmest month (with the lowest average wind speed) is July (5.5mph).
Average humidity in September
O'Fallon, MO
- Average humidity in September: 73%
The month with the highest relative humidity is May (79%).
The month with the lowest relative humidity is October (70%).
Average rainfall in September
O'Fallon, MO
- Average rainfall in September: 1.42"
The wettest month (with the highest rainfall) is May (2.76").
The driest month (with the least rainfall) is December (0.91").
Average rainfall days in September
O'Fallon, MO
- Average rainfall days in September: 11.3 days
The month with the highest number of rainy days is May (15.7 days).
The month with the least rainy days is February (6.8 days).
Average snowfall in September
O'Fallon, MO
- Average snowfall in September: 0"
The month with the highest snowfall is February (1.61").
The months with the least snowfall are April, May, June, July, August, September and October (0").
Average snowfall days in September
O'Fallon, MO
- Average snowfall days in September: 0 days
The months with the highest number of snowfall days are January and February (5.8 days).
The months with the least snowfall days are May, June, July, August, September and October (0 days).
Average daylight in September /
Average sunshine in September
O'Fallon, MO
- Average daylight in September: 12h and 24min
The month with the longest days is June (Average daylight: 14h and 48min).
The month with the shortest days is December (Average daylight: 9h and 30min).
- Average sunshine in September: 9h and 30min
The month with the most sunshine is June (Average sunshine: 10h and 30min).
The months with the least sunshine are January and February (Average sunshine: 4h and 42min).
Average sunshine days in September
O'Fallon, MO
- Average sunshine days in September: 16.7 days
The month with the most sunshine days is December (20.6 days).
The month with the least sunshine days is July (12.6 days).
Average UV index in September
O'Fallon, MO
- Average UV index in September: 5
The months with the highest UV index are May, 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
O'Fallon, MO
- Average cloud cover in September: 28
The month with the most cloud cover is January (Cloud cover 50).
The months with the least cloud cover are June, July, August and September (Cloud cover 28).
Average visibility in September
O'Fallon, MO
- 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).
