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Boise, Idaho climate

BSk Cold semi-arid

Boise has a strongly seasonal cool-temperate climate (Cold semi-arid, Köppen BSk). The hottest month is July with an average daily high near 34°C, while the coldest is December averaging around −4°C at night. Precipitation totals about 292 mm a year and is strongly seasonal — December alone averages 39 mm while August barely receives 4 mm. Light snow accumulates each winter (45 cm of snow per year on average).

☀️ Summers

Hot

Highs near 34°C in July.

About 55 days a year above 32 °C

❄️ Winters

Cold

Lows near −4°C in December.

About 108 freezing nights a year

🌧️ Rain & snow

Fairly dry

About 292 mm of rain a year, plus 45 cm of snow.

Snow falls through the winter months

⛅ Sky & trend

Partly cloudy

A roughly even mix of sun and cloud.

+1.1 °C vs 50 years ago

Temperature & precipitation

Daily high–low temperature range with the monthly average, plus monthly precipitation split into rain and snow · 1991–2020 normals · hover a month for the exact figures

Clear vs cloudy days

Share of days each month that are clear, partly cloudy or cloudy · 1991–2020 · hover a month for the day counts

Boise climate normals (1991–2020)

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Avg high (°C)	4	8	13	17	22	27	34	33	27	18	9	4
Avg temp (°C)	0	3	7	11	16	20	25	24	19	12	5	0
Avg low (°C)	−4	−2	2	4	9	12	17	16	11	5	0	−4
Precipitation (mm)	36	25	34	31	37	19	5	4	11	21	30	39
Snowfall (cm)	13	8	3	0	—	—	—	—	—	0	5	14

Jan – Jun	Jan	Feb	Mar	Apr	May	Jun
Avg high (°C)	4	8	13	17	22	27
Avg temp (°C)	0	3	7	11	16	20
Avg low (°C)	−4	−2	2	4	9	12
Precipitation (mm)	36	25	34	31	37	19
Snowfall (cm)	13	8	3	0	—	—

Jul – Dec	Jul	Aug	Sep	Oct	Nov	Dec
Avg high (°C)	34	33	27	18	9	4
Avg temp (°C)	25	24	19	12	5	0
Avg low (°C)	17	16	11	5	0	−4
Precipitation (mm)	5	4	11	21	30	39
Snowfall (cm)	—	—	—	0	5	14

How often — frequency of weather events

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Days with measurable rain (days)	11	9	10	9	8	5	2	2	4	6	10	12
Days with high ≥ 32°C (days)	—	—	—	0.1	1	7	22	20	5	0.3	—	—
Days with low ≤ 0°C (days)	26	20	11	5	0.8	0.0	—	—	0.2	4	16	25
Days with snowfall ≥ 2.5 cm (days)	2	1	0.5	0.0	—	—	—	—	—	0.1	0.8	2

Jan – Jun	Jan	Feb	Mar	Apr	May	Jun
Days with measurable rain (days)	11	9	10	9	8	5
Days with high ≥ 32°C (days)	—	—	—	0.1	1	7
Days with low ≤ 0°C (days)	26	20	11	5	0.8	0.0
Days with snowfall ≥ 2.5 cm (days)	2	1	0.5	0.0	—	—

Jul – Dec	Jul	Aug	Sep	Oct	Nov	Dec
Days with measurable rain (days)	2	2	4	6	10	12
Days with high ≥ 32°C (days)	22	20	5	0.3	—	—
Days with low ≤ 0°C (days)	—	—	0.2	4	16	25
Days with snowfall ≥ 2.5 cm (days)	—	—	—	0.1	0.8	2

Sky & atmosphere

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Cloud cover (%)	69	66	63	58	55	45	29	30	35	47	63	69
Clear days (≤ 30% cloud)	3	5	6	7	8	12	18	18	16	11	5	3
Partly cloudy days (30–70%)	10	8	10	10	11	9	9	9	9	10	10	11
Cloudy days (≥ 70%)	17	15	15	13	12	8	4	4	6	10	15	17
Relative humidity (%)	81	74	65	59	52	45	33	29	34	48	65	79
Wind speed (m/s)	2.1	2.3	2.3	2.4	2.3	2.3	2.1	2.0	2.0	2.0	2.1	2.2

Jan – Jun	Jan	Feb	Mar	Apr	May	Jun
Cloud cover (%)	69	66	63	58	55	45
Clear days (≤ 30% cloud)	3	5	6	7	8	12
Partly cloudy days (30–70%)	10	8	10	10	11	9
Cloudy days (≥ 70%)	17	15	15	13	12	8
Relative humidity (%)	81	74	65	59	52	45
Wind speed (m/s)	2.1	2.3	2.3	2.4	2.3	2.3

Jul – Dec	Jul	Aug	Sep	Oct	Nov	Dec
Cloud cover (%)	29	30	35	47	63	69
Clear days (≤ 30% cloud)	18	18	16	11	5	3
Partly cloudy days (30–70%)	9	9	9	10	10	11
Cloudy days (≥ 70%)	4	4	6	10	15	17
Relative humidity (%)	33	29	34	48	65	79
Wind speed (m/s)	2.1	2.0	2.0	2.0	2.1	2.2

30-year delta table (1991–2020 minus 1981–2010, °F)

	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Δ Max temp	+1.0	+1.3	+0.9	+0.0	+0.7	+0.1	+1.5	+1.0	+1.2	+0.0	+0.6	+1.3
Δ Avg temp	+0.9	+1.0	+0.7	+0.1	+0.8	+0.3	+1.5	+1.1	+1.4	+0.4	+0.3	+1.4
Δ Min temp	+0.8	+0.7	+0.5	+0.3	+1.0	+0.4	+1.5	+1.2	+1.6	+0.6	-0.2	+1.4

Jan – Jun	Jan	Feb	Mar	Apr	May	Jun
Δ Max temp	+1.0	+1.3	+0.9	+0.0	+0.7	+0.1
Δ Avg temp	+0.9	+1.0	+0.7	+0.1	+0.8	+0.3
Δ Min temp	+0.8	+0.7	+0.5	+0.3	+1.0	+0.4

Jul – Dec	Jul	Aug	Sep	Oct	Nov	Dec
Δ Max temp	+1.5	+1.0	+1.2	+0.0	+0.6	+1.3
Δ Avg temp	+1.5	+1.1	+1.4	+0.4	+0.3	+1.4
Δ Min temp	+1.5	+1.2	+1.6	+0.6	-0.2	+1.4

Methodology & sources

Temperature & precipitation — the official 1991–2020 climate normals from NOAA's U.S. Climate Normals, measured at Boise Air Terminal (NOAA GHCN station USW00024131), about 6 km from the city centre.

Cloud, humidity, wind & sunshine — modelled estimates from NASA POWER, NASA's satellite-and-reanalysis climatology. This is the standard global source for atmospheric variables, which are not measured at most weather stations.

How we build these numbers →