September weather forecastRoundup, MT
September
Weather in September
September signals the onset of fall in Roundup, Montana, USA, with temperatures dropping to less warm degrees. The weather is marked by a decline in rainfall and a slight increase in humidity compared to August. An interesting note for this month is a trivial presence of snowfall, merely 0.12" (3mm), perhaps an early indication of the incoming winter. Despite this, the days still witness ample hours of sunshine, harkening towards pleasant autumn afternoons.Temperature
Roundup's average high-temperature decreases in September, falling from a warm 82.8°F (28.2°C) in August to an agreeable 72.7°F (22.6°C). During September nights, Roundup witnesses a consistent average temperature of 53.2°F (11.8°C).Humidity
The average relative humidity in September is 44%.Rainfall
In September, in Roundup, the rain falls for 8 days. Throughout September, 0.94" (24mm) of precipitation is accumulated. Throughout the year, there are 114.3 rainfall days, and 12.13" (308mm) of precipitation is accumulated.Snowfall
January through May, September through December are months with snowfall. September is the first month it typically snows in Roundup, Montana. Throughout September, in the average 0.3 snowfall days, it receives 0.12" (3mm) of snow. In Roundup, during the entire year, snow falls for 53.5 days and aggregates up to 18.58" (472mm) of snow.Daylight
In Roundup, the average length of the day in September is 12h and 32min.On the first day of September, sunrise is at 6:35 am and sunset at 7:52 pm. On the last day of the month, sunrise is at 7:12 am and sunset at 6:55 pm MDT.
Sunshine
The average sunshine in September in Roundup is 10.2h.UV index
The average daily maximum UV index in September in Roundup, Montana, is 4. A UV Index reading of 3 to 5 represents a moderate threat to health from unprotected exposure to Sun's UV rays for the average person.Note: The maximum UV index of 4 during September leads to these instructions:
Heed the precautions - Suggestions to avoid sunburn are made. The Sun's most intense and consequently most harmful UV radiation during midday hours should be decreased by minimizing exposure and seeking shade. Opt for tightly woven and loose clothing to enhance protection from the Sun. Be mindful! The reflection from snow can increase the Sun's UV radiation nearly twice.
Published by: Weather U.S. | About Us
Data Sources | Weather Forecasting & Climate
Frequently asked questions
Average temperature in September
Roundup, MT
- Average high temperature in September: 72.7°F
The warmest month (with the highest average high temperature) is July (84.7°F).
The month with the lowest average high temperature is December (31.1°F).
- Average low temperature in September: 53.2°F
The month with the highest average low temperature is July (62.4°F).
The coldest month (with the lowest average low temperature) is February (18°F).
Average pressure in September
Roundup, MT
- 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 (29.85"Hg).
Average wind speed in September
Roundup, MT
- Average wind speed in September: 9.3mph
The windiest month (with the highest average wind speed) is January (11.2mph).
The calmest months (with the lowest average wind speed) are July and August (8.5mph).
Average humidity in September
Roundup, MT
- Average humidity in September: 44%
The month with the highest relative humidity is January (77%).
The month with the lowest relative humidity is August (39%).
Average rainfall in September
Roundup, MT
- Average rainfall in September: 0.94"
The wettest month (with the highest rainfall) is May (1.97").
The driest month (with the least rainfall) is January (0.55").
Average rainfall days in September
Roundup, MT
- Average rainfall days in September: 8 days
The month with the highest number of rainy days is May (15.6 days).
The month with the least rainy days is February (4.6 days).
Average snowfall in September
Roundup, MT
- Average snowfall in September: 0.12"
The month with the highest snowfall is February (3.78").
The months with the least snowfall are June, July and August (0").
Average snowfall days in September
Roundup, MT
- Average snowfall days in September: 0.3 days
The month with the highest number of snowfall days is February (11.1 days).
The months with the least snowfall days are June, July and August (0 days).
Average daylight in September /
Average sunshine in September
Roundup, MT
- Average daylight in September: 12h and 30min
The month with the longest days is June (Average daylight: 15h and 48min).
The month with the shortest days is December (Average daylight: 8h and 42min).
- Average sunshine in September: 10h and 12min
The month with the most sunshine is July (Average sunshine: 11h and 48min).
The months with the least sunshine are February and December (Average sunshine: 5h and 12min).
Average sunshine days in September
Roundup, MT
- Average sunshine days in September: 19.5 days
The month with the most sunshine days is September (19.5 days).
The month with the least sunshine days is April (12.8 days).
Average UV index in September
Roundup, MT
- Average UV index in September: 4
The month with the highest UV index is July (UV index 7).
The month with the lowest UV index is December (UV index 1).
Average cloud cover in September
Roundup, MT
- Average cloud cover in September: 22
The month with the most cloud cover is February (Cloud cover 47).
The months with the least cloud cover are July and August (Cloud cover 16).
Average visibility in September
Roundup, MT
- 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).
