Sun Valley (Ketchum), Idaho weather in September
Temperature, rain and sunshine in September: long-term averages from 30 years of weather data, not a forecast.
Holiday weather in September
Excellent
Best time to visit: June, August – September
Best for skiing: December – April
What is the weather like in Sun Valley (Ketchum), Idaho in September?
In September, Sun Valley (Ketchum), Idaho is mild: daytime highs average 21 °C, and nights cool down to about 7 °C. The sun shines for around 8 hours a day. Rain is rare: about 4 days bring 21 mm in total. All in all, September is an excellent month for a holiday in Sun Valley (Ketchum), Idaho.
September compared
How the weather changes from August to October. Tap a month to open it.
| AugustAug | SeptemberSep | OctoberOct | |
|---|---|---|---|
| Score | 90 | 97 | 70 |
| Day | 26° | 21° | 12° |
| Night | 11° | 7° | 0° |
| Sun | 10 h | 8 h | 7 h |
| Rain days | 3 | 4 | 6 |
More details for September
- Daylight
- 12 h 35 min07:15 – 19:50
- UV index
- 6 · highclear sky, noon (estimate)All months
- Muggy days
- 0 daysdew point 18 °C or moreAll months
- Wind
- 14 km/haverage daily peakAll months
- Cloud cover
- 31 %on averageAll months
- Hot days
- 1 day30 °C or moreAll months
- Snow days
- 0 days1 cm or more of fresh snowAll months
- Time zone
- UTC−6America/Boise
How the score comes together
- Temperatureweight 50 %100 %
- Sunshineweight 20 %90 %
- Few rainy daysweight 30 %98 %
Each factor is rated from 0 to 100 % and weighted for the travel style “Mountain air”.
What to pack in September
- Sunscreen
- Sunglasses & sun hat
- A jumper for the evenings
Sun Valley (Ketchum), Idaho in September: quick answers
Is Sun Valley (Ketchum), Idaho hot in September?
No. In September, Sun Valley (Ketchum), Idaho is mild: daytime highs average 21 °C and nights drop to about 7 °C.
Does it rain much in Sun Valley (Ketchum), Idaho in September?
Rain is rare: about 4 days bring 21 mm in total.
Sun Valley (Ketchum), Idaho month by month
The whole year in Sun Valley (Ketchum), IdahoAll destinations: USAWhere to go in September
Climate averages 1996–2025, not a forecast. Data: Copernicus ERA5 / ERA5-Land via Open-Meteo.com (CC BY 4.0), NOAA OISST, WMO 1991–2020 (NOAA NCEI), GeoNames (CC BY 4.0). Sources & licences