Boise, ID Climate & Monthly Averages
The climate of Boise
Seasons are the whole story in Boise. The gap between an average July and an average December is 27°C - big day-to-night temperature swings and modest rainfall - which in practice means 94°F (34°C) afternoons at one end of the calendar and 38°F (4°C) at the other.
Climate quick facts
- Hottest month: July - highs near 94°F (34°C)
- Coldest month: December - highs near 38°F (4°C)
- Decade extremes (2015-2024): 107°F (42°C) high · -10°F (-23°C) low
- Wettest month: December (12 rainy days) · Sunniest: July (14.0 h sun/day)
- Climate type: semi-arid
- Annual swing: 27°C between the average warmest and coolest month · day to night: 12°C
- Snow: about 18 days a year
- Months averaging 30°C or hotter: 2
- Average humidity: 52%
Temperatures through the year
Precipitation concentrates in December - 2.2 inches (56 mm) on 12 days - and thins out by July. December sits at the other end of the year: 38°F (4°C) by day, 25°F (-4°C) at night. Warmth peaks in July: highs of 94°F (34°C), lows of 65°F (18°C). Three of the twelve months pair mild highs with fewer than twelve wet days; the longest unbroken run is September through October.
Rain, sun and snow
Relative humidity averages 52% across the year, drier than all but 8% of the 3496 cities in our dataset. 3 months average under 20 mm of rain, the longest unbroken stretch running July through September. Between the average July and the average December lie 27°C, a wider spread than 92% of the 3496 cities in our dataset. Across the gridded 2015-2024 daily record, the highest daily maximum for this location was 107°F (42°C) and the lowest daily minimum -10°F (-23°C).
How Boise compares
- Annual precipitation is 14.4 inches (365 mm) - drier than all but 10% of the 3496 cities we track.
- Afternoons run 12°C above the following night - a bigger day-to-night gap than 89% of the 3496 cities we track.
Ranked against every city in our dataset, each measured on the same ten-year window.
Monthly climate table
| Month | High | Low | Rain days | Precipitation | Sunshine | Daylight | Wet-day chance | Humidity |
|---|---|---|---|---|---|---|---|---|
| January | 39° | 25° | 10 | 2.0 in | 6.4 h/day | 9.3 h | 34% | 75% |
| February | 45° | 28° | 10 | 1.6 in | 7.5 h/day | 10.4 h | 34% | 66% |
| March | 54° | 34° | 10 | 1.6 in | 9.2 h/day | 11.8 h | 32% | 59% |
| April | 62° | 39° | 7 | 1.3 in | 10.9 h/day | 13.4 h | 23% | 50% |
| May | 71° | 48° | 8 | 1.6 in | 12.2 h/day | 14.7 h | 26% | 49% |
| June | 83° | 57° | 3 | 0.9 in | 13.4 h/day | 15.4 h | 11% | 40% |
| July | 94° | 65° | 1 | 0.1 in | 14.0 h/day | 15.1 h | 3% | 27% |
| August | 91° | 64° | 1 | 0.1 in | 12.9 h/day | 14.0 h | 3% | 30% |
| September | 80° | 55° | 3 | 0.5 in | 11.1 h/day | 12.4 h | 10% | 39% |
| October | 65° | 43° | 5 | 1.0 in | 9.2 h/day | 10.9 h | 15% | 53% |
| November | 49° | 32° | 8 | 1.4 in | 7.1 h/day | 9.6 h | 27% | 65% |
| December | 38° | 25° | 12 | 2.2 in | 5.6 h/day | 8.9 h | 37% | 75% |
Boise month by month
Average high and low for each month, with the bar showing where it sits in Boise's year (left is the coldest night, right is the warmest afternoon).
January
- Rain
- 10 days
- Sunshine
- 6.4 h
- Daylight
- 9.3 h
- Snow
- 4 days
February
- Rain
- 10 days
- Sunshine
- 7.5 h
- Daylight
- 10.4 h
- Snow
- 4 days
March
- Rain
- 10 days
- Sunshine
- 9.2 h
- Daylight
- 11.8 h
- Snow
- 2 days
April
- Rain
- 7 days
- Sunshine
- 10.9 h
- Daylight
- 13.4 h
May
- Rain
- 8 days
- Sunshine
- 12.2 h
- Daylight
- 14.7 h
June
- Rain
- 3 days
- Sunshine
- 13.4 h
- Daylight
- 15.4 h
July
- Rain
- 1 day
- Sunshine
- 14.0 h
- Daylight
- 15.1 h
August
- Rain
- 1 day
- Sunshine
- 12.9 h
- Daylight
- 14.0 h
September
- Rain
- 3 days
- Sunshine
- 11.1 h
- Daylight
- 12.4 h
October
- Rain
- 5 days
- Sunshine
- 9.2 h
- Daylight
- 10.9 h
November
- Rain
- 8 days
- Sunshine
- 7.1 h
- Daylight
- 9.6 h
- Snow
- 2 days
December
- Rain
- 12 days
- Sunshine
- 5.6 h
- Daylight
- 8.9 h
- Snow
- 6 days
Warmer places to go, by month: January · February · March · April · May · June · July · August · September · October · November · December
Seasons in Boise
Spring (March through May)
Spring in Boise stays on the cool side of mild, with daytime highs averaging 62°F (17°C) and nights around 40°F (5°C); expect showers on roughly 25 days across the season, plus about 3 snowy days. Daylight is generous - around 10.8 hours of sun a day.
Summer (June through August)
Summer in Boise is hot, with daytime highs averaging 89°F (32°C) and nights around 62°F (17°C); precipitation is sparse, near 1.1 inches (29 mm) for the season. Daylight is generous - around 13.4 hours of sun a day.
Fall (September through November)
Fall runs cool rather than cold here - highs near 65°F (18°C), nights near 43°F (6°C), and rain comes on about 16 days over the three months.
Winter (December through February)
Winter is brisk and cold here - highs near 41°F (5°C), nights near 26°F (-3°C), and rain falls on around 32 of the 90 days, plus about 14 snowy days.
Climate questions, answered
When is the dry season in Boise?
When does Boise drop below freezing?
How cold does Boise get in winter?
Is Boise a wet city?
Best time to visit Boise
September to October and April is the sweet spot for Boise - temperatures sit either side of the peak heat rather than in it. Expect 72°F (22°C) in the afternoon and around 4 days of rain in a typical month of it. For the same question asked the other way round, see where else is warm in September.
Pack for Boise with lightweight, breathable clothing and serious sun protection, a heavy insulated coat, hat and gloves for winter and rain gear if you travel around December. July nights average 65°F (18°C), so evenings rarely match the afternoons.
Boise temperature records (2015-2024)
Derived from ERA5 reanalysis data, 2015–2024. Official station records may differ. Need the precipitation in other units? The mm-to-inches rainfall converter handles it.