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
As September arrives, Keystone's weather displays a minor decrease in high-temperatures, transitioning from August's warm 80.1°F (26.7°C) to a pleasant 71.4°F (21.9°C). September nights cool down to an average low-temperature of 51.1°F (10.6°C).Humidity
August and September, with an average relative humidity of 52%, are the least humid months in Keystone, South Dakota.Rainfall
In Keystone, in September, during 10 rainfall days, 1.22" (31mm) of precipitation is typically accumulated. Throughout the year, in Keystone, there are 135.4 rainfall days, and 20.39" (518mm) of precipitation is accumulated.Snowfall
January through May, September through December are months with snowfall in Keystone. 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, in Keystone, there are 75.1 snowfall days, and 40.24" (1022mm) of snow is accumulated.Daylight
The average length of the day in September is 12h and 29min.On the first day of the month, sunrise is at 6:18 am and sunset at 7:28 pm. On the last day of September, sunrise is at 6:51 am and sunset at 6:35 pm MDT.
Sunshine
In Keystone, the average sunshine in September is 10.5h.UV index
In September, the average daily maximum UV index is 4. A UV Index estimate of 3 to 5 represents a moderate health risk from exposure to the Sun's UV radiation for average individuals.Note: The maximum UV index of 4 during September leads to these instructions:
Adopt protective measures - Suggestions to resist sunburn are offered. Being exposed to the midday Sun can have harmful effects due to strong UV radiation; always take precautions. Using UVA and UVB-protective sunglasses and sun-protective clothing is effective against UV radiation. Mind you! Snow reflection can increase the intensity of the Sun's UV radiation nearly twofold.
Frequently asked questions
What is the average September temperature in Keystone?
What are the least humid months in Keystone?
What is the average humidity in September in Keystone?
How many days does it rain in September in Keystone?
When does it start to snow in Keystone?
How many hours of daylight does Keystone have in September?
When is the sunrise / sunset in September in Keystone?
How long on average sun shines in September in Keystone?
How high is the UV index in September in Keystone?
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 3min
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 3min
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).
Keystone, South Dakota, USA
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