Boise climate
Boise is warmest in July, with average highs of 34 °C, and coldest in January, when nights average -4.2 °C. December is the wettest month (50 mm) and July the driest (2.7 mm). Figures are 1991–2020 climate normals.
Across a full year Boise averages 318 mm of rain, 117 days above 25 °C and 98 days below freezing.
United States · 823 m elevation · population 235,684 · 1991–2020 normals
Temperature below 0 °C to above 30 °C Rain band height is that month’s share of the wettest month
- Warmest month July 34 °C
- Coldest month January -4.2 °C
- Driest month July 3 mm
- Wettest month December 50 mm
- Least cloud July 21 % cloud
- Hottest on record July 42 °C
- Coldest on record February -24 °C
What to expectBoise through the year
Boise has a clear annual cycle: average daily highs run from 4.1 °C in January to 34 °C in July, a swing of 27 °C in mean temperature across the year.
Counted across a normal year, 117 days a year reach 25 °C, 75 of them reach 30 °C, 98 nights drop below freezing. The warmest reading in the 1991–2020 record is 42 °C, in July.
Rain is strongly seasonal. December averages 50 mm against 3 mm in July — 19 times as much. Planning around the dry months matters more here than planning around temperature.
Month by month
| Month | Avg high | Rainfall | Cloud |
|---|---|---|---|
| January | 4.1 °C | 46 mm | 62 % |
| February | 7.4 °C | 31 mm | 59 % |
| March | 12.7 °C | 36 mm | 59 % |
| April | 17.0 °C | 32 mm | 54 % |
| May | 22.6 °C | 31 mm | 49 % |
| June | 27.7 °C | 18 mm | 38 % |
| July | 33.6 °C | 3 mm | 21 % |
| August | 33.0 °C | 3 mm | 22 % |
| September | 27.2 °C | 11 mm | 28 % |
| October | 18.7 °C | 22 mm | 40 % |
| November | 9.8 °C | 35 mm | 56 % |
| December | 3.9 °C | 50 mm | 62 % |
Temperature month by month
| Month | Avg high | Avg low | Mean | Record high | Record low | Days above 25 °C | Days above 30 °C | Days below 0 °C |
|---|---|---|---|---|---|---|---|---|
| January | 4.1 °C | -4.2 °C | -0.7 °C | 15.0 °C | -23.2 °C | 0 | 0 | 24 |
| February | 7.4 °C | -2.2 °C | 1.8 °C | 17.5 °C | -23.7 °C | 0 | 0 | 19 |
| March | 12.7 °C | 1.2 °C | 6.2 °C | 24.3 °C | -9.3 °C | 0 | 0 | 11 |
| April | 17.0 °C | 4.0 °C | 10.0 °C | 31.4 °C | -4.5 °C | 2 | 0 | 4 |
| May | 22.6 °C | 8.6 °C | 15.4 °C | 37.4 °C | -1.4 °C | 11 | 3 | 0 |
| June | 27.7 °C | 13.0 °C | 20.2 °C | 41.7 °C | 3.6 °C | 20 | 11 | 0 |
| July | 33.6 °C | 17.8 °C | 26.0 °C | 42.0 °C | 8.8 °C | 30 | 26 | 0 |
| August | 33.0 °C | 17.4 °C | 25.2 °C | 41.6 °C | 7.6 °C | 30 | 25 | 0 |
| September | 27.2 °C | 12.6 °C | 19.5 °C | 37.9 °C | 1.0 °C | 20 | 9 | 0 |
| October | 18.7 °C | 6.5 °C | 11.9 °C | 33.9 °C | -8.1 °C | 4 | 1 | 1 |
| November | 9.8 °C | 0.6 °C | 4.4 °C | 23.2 °C | -21.2 °C | 0 | 0 | 13 |
| December | 3.9 °C | -3.6 °C | -0.4 °C | 14.8 °C | -19.6 °C | 0 | 0 | 24 |
Rain, sun and wind month by month
| Month | Rainfall | Wet days | Daylight | Cloud cover | Humidity | Wind |
|---|---|---|---|---|---|---|
| January | 46 mm | 10 | 9.3 h/day | 62 % | 75 % | 17 km/h |
| February | 31 mm | 7 | 10 h/day | 59 % | 70 % | 18 km/h |
| March | 36 mm | 9 | 12 h/day | 59 % | 63 % | 20 km/h |
| April | 32 mm | 7 | 13 h/day | 54 % | 56 % | 21 km/h |
| May | 31 mm | 6 | 15 h/day | 49 % | 50 % | 20 km/h |
| June | 18 mm | 3 | 15 h/day | 38 % | 42 % | 19 km/h |
| July | 3 mm | 1 | 15 h/day | 21 % | 31 % | 17 km/h |
| August | 3 mm | 1 | 14 h/day | 22 % | 31 % | 17 km/h |
| September | 11 mm | 2 | 13 h/day | 28 % | 39 % | 17 km/h |
| October | 22 mm | 4 | 11 h/day | 40 % | 52 % | 18 km/h |
| November | 35 mm | 8 | 9.7 h/day | 56 % | 67 % | 18 km/h |
| December | 50 mm | 10 | 9.0 h/day | 62 % | 73 % | 17 km/h |
Where Boise ranks
| Ranking | Position | Value |
|---|---|---|
| The driest places in North America year-round | 23rdof 50 | 27 mm |
| Places with the best weather in North America in May | 27thof 50 | 92/100 |
| The driest places in North America in July | 28thof 50 | 2.7 mm |
| The driest places in North America in August | 32ndof 50 | 3.1 mm |
| Places with the best weather in North America in June | 39thof 50 | 86/100 |
| The driest places in North America in October | 40thof 50 | 22 mm |
Planning a trip? See the best time to visit Boise.
QuestionsCommon questions about Boise’s climate
When is the best time to visit Boise?
That depends on what you want, so the honest answer is a comparison rather than a single month. May, June, September sit closest to 20 °C on average, July is the warmest month and July the driest. The month-by-month table above has the full picture.
How hot does Boise get?
In July, the warmest month, daily highs average 34 °C. About 75 days a year pass 30 °C. The highest value in the 1991–2020 record is 42 °C.
How cold does it get in winter?
Nights average -4.2 °C in January, the coldest month. A normal year has 98 nights below freezing.
Which month is wettest in Boise?
December, averaging 50 mm over 10 days with rain. The driest month is July with 3 mm. The year as a whole averages 318 mm.
Are these figures a forecast?
No. They are 1991–2020 climate normals: the average of thirty years, which describes what a month is usually like in Boise rather than what any particular week will bring. Individual years can differ substantially from the normal.
Data sources and method
- ERA5 / ERA5-Land reanalysis — Copernicus Climate Change Service (C3S), ECMWF. Copernicus Licence
- Open-Meteo — Open-Meteo.com. CC BY 4.0
- NOAA OISST v2.1 — NOAA Physical Sciences Laboratory. Public domain
- GeoNames — GeoNames.org. CC BY 4.0
- Normal period
- 1991–2020
- Dataset version
- era5-1991-2020-scores1.1
- Last processed
Measured values come from ERA5 reanalysis and are reproduced unchanged. Calculated by us: monthly rankings, daylight hours, beach and comfort scores. Full formulas are on the methodology page.
Contains modified Copernicus Climate Change Service information 2026. Neither the European Commission nor ECMWF is responsible for any use that may be made of the Copernicus information or data it contains.