Yellowstone County Weather in September
Average highs run from 81°F on September 1 to 68°F on September 30, and lows from 48°F to 38°F. Normal precipitation for the month is 1.35 in over about 7 wet days.
September day by day
The normal high and low for each date, and the record, in °F.
- Normal low
- Normal high
- Record high
- Record low
September at a glance
- Average high
- 75°F
- Average low
- 43°F
- Precipitation
- 1.35 in
- Snowfall
- 0.2 in
- Record high
- 103°FSep 1, 1983
- Record low
- 22°FSep 24, 1984
- Chance of a freeze
- 68%
- Days of 90°F or more
- 4.3
- Daylight
- 13 h 17 min to 11 h 45 min
- Cloud cover
- 52%
- Humidity
- 49%
- Dew point
- 38°F
- Wind
- 8.7 mph
Every day of the month
A wet day has at least 0.01 inch of precipitation; snow means at least 0.1 inch of snowfall.
| Date | Normal high | Normal low | Record high | Record low | Chance wet | Chance of snow |
|---|---|---|---|---|---|---|
| Sep 1 | 81°F | 48°F | 103°F 1983 | 43°F 1952 | 20% | 0% |
| Sep 2 | 81°F | 48°F | 99°F 1998 | 35°F 1974 | 21% | 0% |
| Sep 3 | 81°F | 47°F | 101°F 2022 | 39°F 1951 | 21% | 0% |
| Sep 4 | 80°F | 47°F | 100°F 1950 | 31°F 1962 | 21% | 0% |
| Sep 5 | 80°F | 47°F | 102°F 2020 | 37°F 1956 | 21% | 0% |
| Sep 6 | 80°F | 46°F | 97°F 1980 | 36°F 1956 | 21% | 0% |
| Sep 7 | 79°F | 46°F | 102°F 2022 | 34°F 1962 | 21% | 0% |
| Sep 8 | 79°F | 46°F | 99°F 1979 | 32°F 1962 | 22% | 0% |
| Sep 9 | 78°F | 46°F | 95°F 1998 | 31°F 1962 | 22% | 0% |
| Sep 10 | 78°F | 45°F | 92°F 1966 | 33°F 1989 | 22% | 0% |
| Sep 11 | 78°F | 45°F | 96°F 1959 | 28°F 1989 | 22% | 0% |
| Sep 12 | 77°F | 45°F | 93°F 1981 | 30°F 1970 | 22% | 0% |
| Sep 13 | 77°F | 44°F | 92°F 1959 | 29°F 1970 | 22% | 0% |
| Sep 14 | 76°F | 44°F | 97°F 1948 | 31°F 1970 | 23% | 0% |
| Sep 15 | 76°F | 44°F | 95°F 2000 | 31°F 1965 | 23% | 0% |
| Sep 16 | 75°F | 43°F | 94°F 1979 | 29°F 1965 | 23% | 0% |
| Sep 17 | 75°F | 43°F | 91°F 2009 | 26°F 1965 | 23% | 1% |
| Sep 18 | 74°F | 43°F | 92°F 1984 | 28°F 1971 | 23% | 1% |
| Sep 19 | 74°F | 42°F | 93°F 1981 | 26°F 1983 | 23% | 1% |
| Sep 20 | 73°F | 42°F | 90°F 1966 | 26°F 1983 | 23% | 1% |
| Sep 21 | 73°F | 41°F | 88°F 1979 | 28°F 1995 | 23% | 1% |
| Sep 22 | 73°F | 41°F | 88°F 2011 | 25°F 2000 | 23% | 1% |
| Sep 23 | 72°F | 41°F | 91°F 1966 | 23°F 1984 | 23% | 1% |
| Sep 24 | 72°F | 40°F | 92°F 2020 | 22°F 1984 | 23% | 1% |
| Sep 25 | 71°F | 40°F | 95°F 2015 | 26°F 1972 | 23% | 1% |
| Sep 26 | 70°F | 40°F | 93°F 2015 | 25°F 1972 | 23% | 1% |
| Sep 27 | 70°F | 39°F | 91°F 1963 | 27°F 1951 | 23% | 1% |
| Sep 28 | 69°F | 39°F | 92°F 2010 | 26°F 1984 | 23% | 1% |
| Sep 29 | 69°F | 38°F | 94°F 2024 | 26°F 1985 | 23% | 1% |
| Sep 30 | 68°F | 38°F | 90°F 1963 | 23°F 1985 | 23% | 2% |
Chance of rain
- Chance of a wet day
- Chance of snowfall
Sunrise and sunset
Times for 2026, local time (MDT).
- September 1
- sunrise 6:34 AM, sunset 7:51 PM
- September 30
- sunrise 7:10 AM, sunset 6:55 PM
Other months
Sources
Normals: NOAA NCEI U.S. Climate Normals, 1991-2020, station USC00244345 (Huntley Exp Stn), public domain. Records: NOAA GHCN-Daily, station USW00024033, every year on file, quality-flagged values removed. Cloud, humidity, wind and sunshine: NASA POWER (MERRA-2, CERES and GEWEX SRB), 1991-2020. The data was obtained from the National Aeronautics and Space Administration (NASA) Langley Research Center's Prediction Of Worldwide Energy Resources (POWER) project funded through the NASA Earth Science Division: POWER Daily API v2, accessed 2026-09-24. Sun and moon: computed with the NOAA solar equations and Meeus.