Boise, ID climate: monthly averages and frost dates
Boise, ID has cool winters and hot summers by this site's scale, with semi-arid annual precipitation. The figures are the 1991–2020 climate normals for NOAA station USW00024131 (BOISE AIR TERMINAL), 2 mi (4 km) in a straight line from the city's center point (US Census).
- Warmest month high
- 92.7°F
- July
- Coldest month mean
- 32.1°F
- December
- Precipitation
- 11.5 in
- per year
- Snowfall
- 17.6 in
- per year
- Median last frost
- April 24
- 32°F, spring
- Median first frost
- October 21
- 32°F, autumn
Monthly averages in Boise
| Month | High °F | Low °F | Mean °F | Precip. in | Snow in | Days ≥0.01 in | Days ≥90°F | Nights ≤32°F |
|---|---|---|---|---|---|---|---|---|
| January | 38.8 | 25.5 | 32.2 | 1.41 | 5.3 | 11.1 | 0.0 | 25.5 |
| February | 46.0 | 29.0 | 37.5 | 1.00 | 3.3 | 9.1 | 0.0 | 20.1 |
| March | 55.5 | 34.9 | 45.2 | 1.33 | 1.2 | 10.1 | 0.0 | 11.2 |
| April | 62.3 | 39.6 | 50.9 | 1.23 | 0.1 | 9.2 | 0.1 | 5.2 |
| May | 72.3 | 47.5 | 59.9 | 1.45 | 0.0 | 8.4 | 1.4 | 0.8 |
| June | 81.4 | 54.1 | 67.8 | 0.75 | 0.0 | 5.3 | 6.6 | 0.0 |
| July | 92.7 | 61.9 | 77.3 | 0.21 | 0.0 | 2.3 | 22.1 | 0.0 |
| August | 90.7 | 60.8 | 75.8 | 0.17 | 0.0 | 2.1 | 19.5 | 0.0 |
| September | 80.0 | 52.6 | 66.3 | 0.43 | 0.0 | 3.9 | 4.8 | 0.2 |
| October | 64.8 | 41.5 | 53.2 | 0.81 | 0.1 | 6.0 | 0.3 | 3.7 |
| November | 48.8 | 31.7 | 40.3 | 1.18 | 2.0 | 9.7 | 0.0 | 16.3 |
| December | 38.8 | 25.4 | 32.1 | 1.54 | 5.6 | 12.0 | 0.0 | 25.2 |
| Year | 64.3 | 42.0 | 53.2 | 11.51 | 17.6 | 89.2 | 54.9 | 108.2 |
How cold is winter in Boise?
Winters in Boise are cool by this site's scale (coldest-month mean 32 to under 45°F). The coldest month is December, with a mean temperature of 32.1°F (0.1°C), a normal daily high of 38.8°F (3.8°C) and a normal daily low of 25.4°F (−3.7°C).
The station averages 108.2 nights a year at or below 32°F and 16.3 days when the high stays at or below 32°F.
The normal daily low is at or below freezing in November to February.
How hot is summer in Boise?
Summers in Boise are hot by this site's scale (hottest-month high 90 to under 100°F). July has the highest normal daily high, 92.7°F (33.7°C), with nights averaging 61.9°F (16.6°C).
The high reaches 90°F or more on 54.9 days in a normal year.
The normal daily high itself is 90°F or above in July and August.
What is the wettest month in Boise?
Boise gets 11.51 in (292 mm) of precipitation in a normal year, which this site classes as semi-arid (10 to under 20 in a year). The wettest month is December with 1.54 in (39 mm); the driest is August with 0.17 in (4 mm).
Measurable precipitation (0.01 in or more) falls on 89.2 days a year.
Does it snow in Boise?
Normal annual snowfall in Boise is 17.6 in (45 cm), which this site classes as moderate (12 to under 36 in a year).
December is the snowiest month, with 5.6 in (14 cm).
A day with 1.0 in or more of snowfall comes 6.1 times a year on average.
Which months are mild in Boise?
3 months in Boise meet this site's comfort thresholds (normal high 65–85°F, low 45°F or higher, fewer than 10 days with 0.10 in or more of precipitation): May, June and September.
Thresholds and their limits: methodology.
Frost dates and growing season in Boise
In Boise the median last spring night at or below 32°F is April 24, and the median first autumn one is October 21 (NOAA P50 dates). NOAA's median length of the freeze-free season is 179 days. NOAA takes that median over each year's own season, so it need not equal the 180 days between the two median dates.
There is still a 10% chance of a 32°F night on or after May 9, and a 10% chance that the first one has come by October 5.
The chance that the last spring 32°F night comes on or after April 4 is 90%.
For a hard freeze (28°F or lower) the median dates are April 2 in spring and October 31 in autumn.
| Chance | Last spring 32°F night on or after | First autumn 32°F night by | Freeze-free season, days |
|---|---|---|---|
| 10% | May 9 | October 5 | 203 |
| 20% | May 4 | October 10 | 196 |
| 30% | April 30 | October 14 | 190 |
| 40% | April 27 | October 18 | 185 |
| 50% | April 24 | October 21 | 179 |
| 60% | April 21 | October 24 | 175 |
| 70% | April 17 | October 27 | 171 |
| 80% | April 12 | October 31 | 164 |
| 90% | April 4 | November 5 | 156 |
| Threshold | Median last date (spring) | Median first date (autumn or winter) | Median season, days |
|---|---|---|---|
| 36°F | May 8 | October 8 | 153 |
| 32°F | April 24 | October 21 | 179 |
| 28°F | April 2 | October 31 | 212 |
| 24°F | March 9 | November 13 | 246 |
| 20°F | February 19 | November 25 | 280 |
| 16°F | February 2 | December 7 | 311 |
| Jan | Feb | Mar | Apr | May | Jun | Jul | Aug | Sep | Oct | Nov | Dec |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 100% | 100% | 100% | 90% | 28% | 0% | 0% | 0% | 3% | 80% | 100% | 100% |
Nearby and similar places
Of the places on this site, the closest to Boise by station distance are Spokane, WA at 287 mi (462 km), Salt Lake City, UT at 291 mi (469 km) and Portland, OR at 343 mi (551 km).
Among places whose winter, summer and precipitation words are each within one band of Boise's (winter: cool, summer: hot, precipitation: semi-arid), the closest monthly temperature and precipitation patterns are Salt Lake City, UT, Spokane, WA and Billings, MT.
Compared with Spokane, WA, Boise's peak-month normal high is 8.3°F (4.6°C) higher, its coldest-month mean is 3.0°F (1.7°C) higher, and its annual precipitation is 4.94 in less.
| Place | Listed as | Station distance | Coldest mean °F | Warmest high °F | Precip. in/yr | Snow in/yr | Last frost |
|---|---|---|---|---|---|---|---|
| Boise, ID | this page | – | 32.1 | 92.7 | 11.5 | 17.6 | April 24 |
| Spokane, WA | nearby, similar | 287 mi (462 km) | 29.1 | 84.4 | 16.4 | 45.4 | April 26 |
| Salt Lake City, UT | nearby, similar | 291 mi (469 km) | 31.4 | 94.0 | 15.5 | 51.9 | April 8 |
| Portland, OR | nearby | 343 mi (551 km) | 41.6 | 82.3 | 36.9 | 4.2 | March 13 |
| Billings, MT | similar | 408 mi (657 km) | 27.0 | 87.3 | 14.3 | 57.4 | May 4 |
How nearby and similar places are chosen: methodology.
Source and station
The data for Boise come from NOAA station BOISE AIR TERMINAL, ID US (USW00024131) at 43.5667, -116.2406, elevation 2,814 ft (858 m). It lies 2 mi (4 km) in a straight line from the center point of Boise City city, the “internal point” in the US Census 2024 Gazetteer.
Each monthly normal used here rests on at least 26 years of data from 1991–2020 (NOAA's per-field year counts).
NOAA completeness flags on the monthly fields used here:
- S: Standard: meets WMO standards for data availability for 24 or more years.
Cite the data as:
Palecki, Michael; Durre, Imke; Applequist, Scott; Arguez, Anthony; Lawrimore, Jay (2021). U.S. Climate Normals 2020: U.S. Monthly Climate Normals (1991-2020). Station USW00024131 (BOISE AIR TERMINAL, ID US). NOAA National Centers for Environmental Information. Dataset. https://doi.org/10.25921/wck8-er13. Accessed 2026-10-09.
Palecki, Michael; Durre, Imke; Applequist, Scott; Arguez, Anthony; Lawrimore, Jay (2021). U.S. Climate Normals 2020: U.S. Annual/Seasonal Climate Normals (1991-2020). Station USW00024131 (BOISE AIR TERMINAL, ID US). NOAA National Centers for Environmental Information. Dataset. https://doi.org/10.25921/4ek7-fk11. Accessed 2026-10-09.
Files used: monthly normals CSV, annual/seasonal normals CSV (retrieved 2026-10-09). The values on this page as JSON: /us/id/boise/data.json.