Sun Valley, ID weather in September
Sun Valley is mild and mostly dry in September: highs average 69°F and nights drop to about 36°F. Rain falls on about 4 days. A great month for outdoor plans.
- Normal high
- 69°F
- Normal low
- 36°F
- Wet days
- 4
- 1.0 in total
- Muggy days
- 0
- dew point 65°F+
How September changes from start to finish
| September 1 | September 30 | |
|---|---|---|
| Normal high | 74°F | 63°F |
| Normal low | 40°F | 33°F |
| Chance of a wet day | 14% | 15% |
| Sunrise / sunset | 7:01 am / 8:13 pm | 7:33 am / 7:20 pm |
| Daylight | 13.2 h | 11.8 h |
Chance of a wet day: average for the first and last 7 days of the month. Times are local clock time (Mountain Time).
What kind of days to expect
- Comfortable dayshigh 65-80°F and dew point under 60°F20 of 30
- Hot dayshigh 90°F or more0 of 30
- Muggy daysdaily mean dew point 65°F or more0 of 30
- Wet daysat least 0.01 in of rain or melted snow4 of 30
- Notable rainat least 0.10 in2 of 30
- Freezing nightslow 32°F or below9 of 30
Average days per September, counted from daily records for each year 1991-2020.
Rain in September
Normal precipitation is 1.0 in; a dry September brings about 0.2 in and a wet one about 1.2 in (25th and 75th percentiles). About 1 day brings half an inch or more. Snow is very rare.
How September varies from year to year
- Warmest September, 1991-20202009: average high 75°F
- Coolest September2019: average high 66°F
- Wettest September2000: 3.0 in
- Driest September1999: no measurable precipitation
- Highest reading90°F (September 6, 2020)
- Lowest reading14°F (September 24, 2008)
From the station's daily records with NOAA quality flags removed; most recent date shown when a reading repeats.
September compared with August and October
| August | September | October | |
|---|---|---|---|
| Normal high | 79°F | 69°F | 56°F |
| Normal low | 44°F | 36°F | 28°F |
| Wet days | 4 | 4 | 5 |
| Comfortable days | 16 | 20 | 6 |
| Daylight | 13.9 h | 12.5 h | 11.0 h |
Highs change by -10°F from August and -13°F into October.
Nearby alternatives in September
- Warmer: Boise, ID93 mi · high 80°F · 4 wet days
How Sun Valley ranks in September
- Normal high357th warmest of 378 cities; 2nd of 2 in Idaho
- Wet days78th driest of 378
- Comfortable days19th most of 342
What to pack for Sun Valley in September
- A warm jacket – lows near 36°F, highs near 69°F
- Layers – afternoons near 69°F but nights near 36°F
Heating and cooling
September has 374 heating degree days and 1 cooling degree days (base 65°F), 4% of the year's total heating and cooling demand.
Questions
How cold is Sun Valley in September?
The normal high is 69°F and the normal low is 36°F. From 1991 to 2020 the coldest September reading was 14°F (September 24, 2008).
Does it rain a lot in Sun Valley in September?
About 4 days in September have at least 0.01 in of precipitation, and the normal total is 1.0 in. The wettest September in 1991-2020 was in 2000 (3.0 in); the driest was in 1999, with no measurable precipitation.
Does it snow in Sun Valley in September?
Snow is very rare: the 1991-2020 normal for September rounds to 0.0 in.
Where the numbers come from
- Temperature, rain and snowfall: Ketchum RS (USC00104845), 1.0 mi SSW of the city center, 5,890 ft (62 ft lower than the city). NOAA normals and daily records, 1991-2020.
- Frost dates: Bellevue (USC00100774), 17 mi SSE of the city center, 5,192 ft (760 ft lower than the city). NOAA normals and daily records, 1991-2020.
- Daily humidity and wind: Stanley Ranger Station (726824-04112), 44 mi NW of the city center, 6,495 ft (543 ft higher than the city). Hourly observations, 1991-2020.
- Not available for this location: snow depth, humidity and wind by hour and cloud cover (no station close enough or similar enough in elevation).