Boise, ID weather in September
September in Boise: warm and mostly dry. Highs 80°F, lows 53°F, about 4 wet days. A good month for most outdoor plans.
- Normal high
- 80°F
- Normal low
- 53°F
- Wet days
- 4
- 0.4 in total
- Muggy days
- 0
- dew point 65°F+
How September changes from start to finish
| September 1 | September 30 | |
|---|---|---|
| Normal high | 86°F | 74°F |
| Normal low | 57°F | 48°F |
| Chance of a wet day | 11% | 15% |
| Sunrise / sunset | 7:08 am / 8:20 pm | 7:41 am / 7:28 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).
A typical September day
- 6 am54°Fdew point 37°F
- 9 am63°Fdew point 39°F
- Noon73°Fdew point 38°F
- 3 pm78°Fdew point 37°F
- 6 pm76°Fdew point 36°F
- 9 pm65°Fdew point 38°F
NOAA hourly normals (local standard time) from Boise Air Terminal (4 mi away); average wind 7 mph; clear or few clouds in 88% of daytime hours, mostly cloudy or overcast in 9%.
What kind of days to expect
- Comfortable dayshigh 65-80°F and dew point under 60°F13 of 30
- Hot dayshigh 90°F or more5 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 in1 of 30
- Freezing nightslow 32°F or below0 of 30
- Snow on the groundsnow depth 1 in or more0 of 30
Average days per September, counted from daily records for each year 1991-2020.
Rain in September
Normal precipitation is 0.4 in; a dry September brings about 0.06 in and a wet one about 0.6 in (25th and 75th percentiles). Days with half an inch or more are rare.
How September varies from year to year
- Warmest September, 1991-20202011: average high 86°F
- Coolest September1996: average high 75°F
- Wettest September1998: 2.0 in
- Driest September1993: no measurable precipitation
- Highest reading102°F (September 4, 2020)
- Lowest reading30°F (September 21, 1993)
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 | 91°F | 80°F | 65°F |
| Normal low | 61°F | 53°F | 42°F |
| Wet days | 2 | 4 | 6 |
| Comfortable days | 3 | 13 | 13 |
| Daylight | 13.9 h | 12.5 h | 11.0 h |
Highs change by -11°F from August and -15°F into October.
Nearby alternatives in September
- Cooler: Sun Valley, ID93 mi · high 69°F · 4 wet days
How Boise ranks in September
- Normal high199th warmest of 378 cities; 1st of 2 in Idaho
- Wet days75th driest of 378
- Comfortable days128th most of 342
What to pack for Boise in September
- Layers – afternoons near 80°F but nights near 53°F
Heating and cooling
September has 80 heating degree days and 119 cooling degree days (base 65°F), 3% of the year's total heating and cooling demand.
Questions
How hot is Boise in September?
The normal high is 80°F and the normal low is 53°F. From 1991 to 2020 the hottest September reading was 102°F (September 4, 2020).
Does it rain a lot in Boise in September?
About 4 days in September have at least 0.01 in of precipitation, and the normal total is 0.4 in. The wettest September in 1991-2020 was in 1998 (2.0 in); the driest was in 1993, with no measurable precipitation.
Is September a good time to visit Boise?
September ranks 4th of 12 months on our comfort score for Boise (66 out of 100). It has about 13 comfortable days and about 5 days at 90°F or hotter. The best month is May.
Where the numbers come from
- Temperature, rain, snowfall, snow depth, frost dates, humidity and wind by hour and cloud cover: Boise Air Terminal (USW00024131), 3.7 mi SSW of the city center, 2,814 ft (114 ft higher than the city). NOAA normals and daily records, 1991-2020.
- Daily humidity and wind: Boise Air Terminal/Gowen Fd Airport (726810-24131), 3.7 mi SSW of the city center, 2,823 ft (123 ft higher than the city). Hourly observations, 1991-2020.