Boise climate — normals and trends
Boise (United States) has a cold semi-arid climate (BSk) under the Köppen-Geiger classification. Its mean annual temperature is 11.5 °C and it receives 340 mm of precipitation per year.
These figures are normals computed over 86 complete calendar years, from 1940 to 2025, using ERA5 reanalysis data from the Copernicus programme.
The warmest month is July (25.5 °C on average) and the coldest is January (-0.9 °C). Rainfall peaks in December.
Boise averages 93 frost days, 69 hot days (≥ 30 °C) and 75 rainy days per year.
Boise has warmed by +2.1 °C between 1940 and 2025, or +0.25 °C per decade. This trend is statistically significant.
The number of frost days there went from about 109 to 77 per year over the period.
The hottest day of the period reached 43.5 °C (on 4 August 1961) and the coldest -31.9 °C (on 22 December 1990).
Data from ERA5 reanalysis (Copernicus Climate Change Service), redistributed under a CC-BY 4.0 licence. Normals are recomputed whenever the archive is updated.
Climate normals · ERA5
BoiseIdaho
- coords
- 43.61°, -116.20°
- period
- 1940–2025 · 86 yrs
Mean daily temperature
11.5°C
Average daily high
17.5°C
Average daily low
5.7°C
Annual rainfall
340mm
Sunshine / day
10.4h
Mean relative humidity
52%
Average peak wind
17.4km/h
Seasonal range
26.4°C
Frost days (< 0 °C)
93 d/yr
Hot days (≥ 30 °C)
69 d/yr
Rainy days (≥ 1 mm)
75 d/yr
Annual snowfall
46.4 cm
Average feels-like high
14.4 °C
Average feels-like low
2.3 °C
Average peak gust
34.2 km/h
Tropical nights (≥ 20 °C)
11 d/yr
Solar radiation
17.4 MJ/m²
Has the climate changed?
One stripe per year, 1940 to 2025
+2.1 °C
since 1940
+0.3 °C per decade · r² = 0.39 · p = < 0.001
Trend fitted by linear regression (ordinary least squares) on annual means. A trend is shown only when it is statistically significant (p < 0.05).
A climograph overlays rainfall (bars) and temperature (line): the standard reading in climatology, where you can see at a glance whether the warm season is also the dry one.
Records for the period
Hottest day
43.5 °C
4 August 1961
Coldest day
-31.9 °C
22 December 1990
Wettest day
45 mm
14 September 1959
Windiest day
47.5 km/h
26 January 1969
Strongest gust
89.3 km/h
26 October 1950
Hottest feels-like
43.5 °C
12 July 2002
Coldest feels-like
-37.6 °C
22 December 1990
Snowiest day
11.2 cm
23 January 1982
Sunniest day
14.9 h
28 June 2012
Normals computed over complete calendar years 1940–2025.
A specific year
Pick a year and see how it compares to normal — warmer, drier or more extreme than usual?
Across the whole year
Month by month
| High | vs. normal | Precipitation | vs. normal | |
|---|---|---|---|---|
| Jan | 4.2 °C | +1.1 °C | 28 mm | -17 mm |
| Feb | 6.1 °C | -0.7 °C | 82 mm | +44 mm |
| Mar | 13.7 °C | +2.0 °C | 36 mm | -4 mm |
| Apr | 18.8 °C | +2.1 °C | 10 mm | -23 mm |
| May | 24.3 °C | +2.3 °C | 18 mm | -11 mm |
| Jun | 29.3 °C | +2.2 °C | 1 mm | -16 mm |
| Jul | 33.4 °C | +0.3 °C | 7 mm | +3 mm |
| Aug | 32.2 °C | +0.3 °C | 18 mm | +11 mm |
| Sep | 28.6 °C | +2.6 °C | 4 mm | -9 mm |
| Oct | 16.8 °C | -1.4 °C | 44 mm | +20 mm |
| Nov | 12.8 °C | +3.6 °C | 16 mm | -25 mm |
| Dec | 9.7 °C | +5.7 °C | 72 mm | +22 mm |
The year's extremes
What was the weather like that day?
Your birthday, a wedding, a memorable trip: discover the actual weather for any date since 1940.
Frequently asked questions
What is the climate of Boise?
Boise has a cold semi-arid climate (Köppen BSk). Over 1940-2025, the average annual temperature is 11.5 °C and it receives 340 mm of precipitation per year.
What is the hottest day ever recorded in Boise?
The hottest day measured in Boise between 1940 and 2025 was 4 August 1961, reaching 43.5 °C.
What is the coldest day in Boise?
The coldest day measured in Boise between 1940 and 2025 was 22 December 1990, at -31.9 °C.
Does it snow in Boise?
Yes. Boise gets on average 46.4 cm of snow per year and has around 93 frost days.
Has the climate of Boise warmed?
Yes: Boise warmed by +2.1 °C between 1940 and 2025, a statistically significant trend.
What is the wettest day in Boise?
The wettest day measured in Boise between 1940 and 2025 was 14 September 1959, with 45 mm of rain in 24 hours.
What was the windiest day in Boise?
The windiest day measured in Boise between 1940 and 2025 was 26 January 1969, with winds reaching 47.5 km/h.
What is the warmest month in Boise?
The warmest month in Boise is July (25.5 °C on average); the coldest is January (-0.9 °C).
How much does it rain in Boise?
Boise receives on average 340 mm of precipitation per year, spread over about 75 rainy days.
Is it sunny in Boise?
Boise gets on average 10.4 hours of sunshine per day, roughly 3,796 hours per year over 1940-2025.
What is the biggest single-day snowfall in Boise?
The heaviest 24-hour snowfall measured in Boise between 1940 and 2025 was 23 January 1982, with 11.2 cm.
Are there tropical nights in Boise?
Yes: Boise has on average 11 tropical nights per year (temperature staying above 20 °C), over 1940-2025.
What was the most extreme apparent temperature in Boise?
In Boise, between 1940 and 2025, the highest apparent temperature reached 43.5 °C on 12 July 2002, and the lowest was -37.6 °C on 22 December 1990.
Compare Boise with another city
Pick a second city: its normals will be set against these, indicator by indicator.
Nearby cities
The climate around Boise