September weather forecastKeystone, SD
September
Weather in September
September in Keystone introduces the initial hints of the fall season, evident in the drop in temperatures and shortening daylight hours. Temperatures begin their descent with highs hitting around 71.4°F (21.9°C), a direct contrast to the sizzling heat of August. The amount of rainfall dropped significantly in September, indicating a drying trend. The landscape starts to wear the vibrant hues of autumn, providing a scenic backdrop. With the arrival of October, an even more noticeable drop in temperature can be expected, signaling a steady approach towards the cold season.Temperature
A modest decline in the average high-temperature is seen during September, decreasing from a moderately hot 80.1°F (26.7°C) in August to an agreeable 71.4°F (21.9°C). In the month of September, the average temperature dips to a cool 51.1°F (10.6°C) during the night.Humidity
August and September, with an average relative humidity of 52%, are the least humid months in Keystone, South Dakota.Rainfall
In September, the rain falls for 10 days. Throughout September, 1.22" (31mm) of precipitation is accumulated. Throughout the year, there are 135.4 rainfall days, and 20.39" (518mm) of precipitation is accumulated.Snowfall
Months with snowfall are January through May, September through December. September is the first month it typically snows. Throughout September, in the average 0.4 snowfall days, it receives 0.35" (9mm) of snow. Throughout the year, there are 75.1 snowfall days, and 40.24" (1022mm) of snow is accumulated.Daylight
In Keystone, the average length of the day in September is 12h and 29min.On the first day of September, sunrise is at 6:18 am and sunset at 7:28 pm. On the last day of the month, sunrise is at 6:51 am and sunset at 6:35 pm MDT.
Sunshine
In September, the average sunshine is 10.5h.UV index
The average daily maximum UV index in September is 4. A UV Index estimate of 3 to 5 represents a moderate health risk from unsafe exposure to UV radiation for the average person.Note: During September, 4 as the daily maximum UV index converts into the following advice:
Take measures. Individuals with light skin might experience burns in under 30 minutes. Midday is the peak time for the Sun's radiation; stay in the shade and protect yourself. Sun-protective clothing, a long-sleeved shirt and pants, a wide-brimmed hat, and UVA and UVB-blocking sunglasses are particularly helpful in blocking UV radiation's harmful effects. Beware! Reflection from snow can magnify the Sun's UV radiation nearly twofold.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
Average temperature in September
Keystone, SD
- Average high temperature in September: 71.4°F
The warmest month (with the highest average high temperature) is July (81.7°F).
The month with the lowest average high temperature is December (29.8°F).
- Average low temperature in September: 51.1°F
The month with the highest average low temperature is July (60.4°F).
The coldest month (with the lowest average low temperature) is February (16.2°F).
Average pressure in September
Keystone, SD
- Average pressure in September: 29.93"Hg
The month with the highest atmospheric pressure is January (30.13"Hg).
The month with the lowest atmospheric pressure is June (29.84"Hg).
Average wind speed in September
Keystone, SD
- Average wind speed in September: 8.1mph
The windiest month (with the highest average wind speed) is April (9.5mph).
The calmest month (with the lowest average wind speed) is August (7mph).
Average humidity in September
Keystone, SD
- Average humidity in September: 52%
The months with the highest relative humidity are January and February (77%).
The months with the lowest relative humidity are August and September (52%).
Average rainfall in September
Keystone, SD
- Average rainfall in September: 1.22"
The wettest month (with the highest rainfall) is June (3.19").
The driest month (with the least rainfall) is January (0.47").
Average rainfall days in September
Keystone, SD
- Average rainfall days in September: 10 days
The month with the highest number of rainy days is May (18.6 days).
The month with the least rainy days is November (4.5 days).
Average snowfall in September
Keystone, SD
- Average snowfall in September: 0.35"
The month with the highest snowfall is April (7.24").
The months with the least snowfall are June, July and August (0").
Average snowfall days in September
Keystone, SD
- Average snowfall days in September: 0.4 days
The month with the highest number of snowfall days is February (12.9 days).
The months with the least snowfall days are June, July and August (0 days).
Average daylight in September /
Average sunshine in September
Keystone, SD
- Average daylight in September: 12h and 30min
The month with the longest days is June (Average daylight: 15h and 24min).
The month with the shortest days is December (Average daylight: 9h and 0min).
- Average sunshine in September: 10h and 30min
The month with the most sunshine is August (Average sunshine: 11h and 42min).
The month with the least sunshine is February (Average sunshine: 6h and 0min).
Average sunshine days in September
Keystone, SD
- Average sunshine days in September: 17.3 days
The month with the most sunshine days is November (19.2 days).
The month with the least sunshine days is May (7.8 days).
Average UV index in September
Keystone, SD
- Average UV index in September: 4
The month with the highest UV index is July (UV index 6).
The months with the lowest UV index are January, February, March, October, November and December (UV index 2).
Average cloud cover in September
Keystone, SD
- Average cloud cover in September: 18
The month with the most cloud cover is April (Cloud cover 38).
The month with the least cloud cover is August (Cloud cover 17).
Average visibility in September
Keystone, SD
- 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).
