Hot, dry summers, short cold winters and four real seasons
By J&H Digital Services LLCChecked Oct 20265 sources
Boise has a high-desert climate with four distinct seasons. Summers are hot and dry, with about 55 days a year at 90°F or above. Winters are cold but usually mild by mountain standards, with about 17.6 inches of snow in an average year. The valley gets only about 11.5 inches of rain and melted snow a year.
| Month | Avg high °F | Avg low °F | Precipitation (in) | Snowfall (in) |
|---|---|---|---|---|
| January | 38.8 | 25.5 | 1.41 | 5.3 |
| February | 46.0 | 29.0 | 1.00 | 3.3 |
| March | 55.5 | 34.9 | 1.33 | 1.2 |
| April | 62.3 | 39.6 | 1.23 | 0.1 |
| May | 72.3 | 47.5 | 1.45 | 0.0 |
| June | 81.4 | 54.1 | 0.75 | 0.0 |
| July | 92.7 | 61.9 | 0.21 | 0.0 |
| August | 90.7 | 60.8 | 0.17 | 0.0 |
| September | 80.0 | 52.6 | 0.43 | 0.0 |
| October | 64.8 | 41.5 | 0.81 | 0.1 |
| November | 48.8 | 31.7 | 1.18 | 2.0 |
| December | 38.8 | 25.4 | 1.54 | 5.6 |
| Year | 64.3 | 42.0 | 11.51 | 17.6 |
Measured at Boise Airport. Precipitation includes rain and melted snow. Nampa and Caldwell run a little warmer in summer; the foothills and Boise Bench can see more snow than the airport. Snow totals vary a lot from year to year. Source: NWS Boise: NOWData (NOAA 1991 to 2020 normals)
Hot, sunny and very dry. July and August highs average 90 to 93°F, and a typical summer has about nine days at 100°F or more. Low humidity means nights cool off into the 60s or high 50s. July and August get only about two days of measurable rain each. Wildfire smoke can drift in from late July into September; see our air quality guide.
Often the nicest time of year: warm, clear days and crisp nights. The first freeze usually comes around mid-October. Rain and the first valley snow return in November.
Cold and often gray. Highs average in the high 30s to mid 40s and lows in the mid to high 20s. Snow usually comes in small storms of an inch or a few inches and often melts within days. Some weeks bring , when cold, hazy air gets trapped in the valley while the mountains above are sunny.
Changeable and windy, with warm days followed by cold snaps. Spring brings some of the year's steadier rain, though totals are still small. The last spring freeze usually comes in early May, so wait until mid-May to plant tender garden plants.
| Measure | Boise |
|---|---|
| Typical last spring freeze (32°F) | Around May 2 |
| Typical first fall freeze (32°F) | Around October 17 |
| Typical frost-free season | About 168 days |
Medians we calculated from Boise daily low temperatures, 1991 to 2020. In about half of years the last freeze comes later than the date shown, so cover tender plants on cold nights into mid-May. Outlying areas such as Kuna, Star and Middleton can freeze earlier in fall and later in spring. Source: NOAA ACIS: Boise daily data
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