Boise, Idaho climate: Normal weather by month, frost dates and records
Boise's normal year runs from 25°F December nights to 93°F July afternoons, with 11.5 inches of precipitation and 18 inches of snow a year. (NOAA 1991-2020 normals)
In metric: a yearly mean of 11.8°C, December lows of −4°C, July highs of 34°C, 292 mm of precipitation a year.
- NOAA stationBoise Air Terminal
- Station IDUSW00024131
- Location43.57°N 116.24°W
- Elevation2,814 ft (858 m)
- From the center2 miles
- Population237,963
On October 23, the normal high in Boise is 61°F and the normal low 39°F, and the chance of measurable rain or snow is 22%.
Normals describe a typical year at the station, not a forecast. The National Weather Service forecast for Boise.
- Jan 39° 26°
- Feb 46° 29°
- Mar 56° 35°
- Apr 62° 40°
- May 72° 48°
- Jun 81° 54°
- Jul 93° 62°
- Aug 91° 61°
- Sep 80° 53°
- Oct 65° 42°
- Nov 49° 32°
- Dec 39° 25°
Each month: normal high (large) and low, °F. Fill: the month's normal mean, colder blue to hotter red.
What is the weather like in Boise each month?
July is the warmest month, with normal highs of 93°F; December the coldest, with normal lows of 25°F. The most precipitation falls in December (1.54 in), the least in August (0.17 in).
Each month has its own page with the day-by-day normals, the month's records and its recent years:
| Month | High | Low | Mean | Precip. | Snow | Wet days | 90°F days | Freezing nights | Daylight |
|---|---|---|---|---|---|---|---|---|---|
| January | 39°F | 26°F | 32.2°F | 1.41 | 5.3 | 11 | <1 | 26 | 9 h 20 min |
| February | 46°F | 29°F | 37.5°F | 1.00 | 3.3 | 9 | <1 | 20 | 10 h 30 min |
| March | 56°F | 35°F | 45.2°F | 1.33 | 1.2 | 10 | <1 | 11 | 11 h 50 min |
| April | 62°F | 40°F | 50.9°F | 1.23 | 0.1 | 9 | <1 | 5 | 13 h 20 min |
| May | 72°F | 48°F | 59.9°F | 1.45 | 0.0 | 8 | 1 | 1 | 14 h 40 min |
| June | 81°F | 54°F | 67.8°F | 0.75 | 0.0 | 5 | 7 | <1 | 15 h 20 min |
| July | 93°F | 62°F | 77.3°F | 0.21 | 0.0 | 2 | 22 | <1 | 15 h 10 min |
| August | 91°F | 61°F | 75.8°F | 0.17 | 0.0 | 2 | 20 | <1 | 14 h |
| September | 80°F | 53°F | 66.3°F | 0.43 | 0.0 | 4 | 5 | <1 | 12 h 30 min |
| October | 65°F | 42°F | 53.2°F | 0.81 | 0.1 | 6 | <1 | 4 | 11 h 10 min |
| November | 49°F | 32°F | 40.3°F | 1.18 | 2.0 | 10 | <1 | 16 | 9 h 40 min |
| December | 39°F | 25°F | 32.1°F | 1.54 | 5.6 | 12 | <1 | 25 | 9 h |
| Year (annual) | 64°F | 42°F | 53.2°F | 11.51 | 17.6 | 89 | 55 | 108 |
The same normals in °C and millimetres
| Month | High | Low | Mean | Precip. | Snow |
|---|---|---|---|---|---|
| January | 4°C | −4°C | 0.1°C | 36 mm | 13 cm |
| February | 8°C | −2°C | 3.1°C | 25 mm | 8 cm |
| March | 13°C | 2°C | 7.3°C | 34 mm | 3 cm |
| April | 17°C | 4°C | 10.5°C | 31 mm | 0 cm |
| May | 22°C | 9°C | 15.5°C | 37 mm | 0 cm |
| June | 27°C | 12°C | 19.9°C | 19 mm | 0 cm |
| July | 34°C | 17°C | 25.2°C | 5 mm | 0 cm |
| August | 33°C | 16°C | 24.3°C | 4 mm | 0 cm |
| September | 27°C | 11°C | 19.1°C | 11 mm | 0 cm |
| October | 18°C | 5°C | 11.8°C | 21 mm | 0 cm |
| November | 9°C | 0°C | 4.6°C | 30 mm | 5 cm |
| December | 4°C | −4°C | 0.1°C | 39 mm | 14 cm |
Source: NOAA NCEI 1991-2020 monthly normals, station USW00024131; annual normals. Wet days: 0.01 inch or more; 90°F days and freezing nights: NOAA's day counts. Daylight: sunrise to sunset on the 15th, computed from the latitude.
When is the best weather to visit Boise?
Normal highs sit between 65°F and 85°F in May, June and September. Of those, September has the fewest days with rain (4).
That is a measurement, not a recommendation: it counts the months whose normal afternoon high sits between 65°F and 85°F, where a light layer is enough by day.
Source: NOAA NCEI 1991-2020 monthly normals, station USW00024131.
When is the last frost in Boise?
In Boise, the last spring frost (32°F) comes after April 24 in half of years and after May 9 in one year in ten; the first autumn frost comes before October 21 in half of years and before October 5 in one year in ten.
Frost-free in half of yearsFrost in 1 to 9 years out of 10Frost most years
- Last spring frost, half of years after
- April 241 year in 10 after May 9; 9 in 10 after April 4
- First autumn frost, half of years before
- October 211 year in 10 before October 5; 9 in 10 before November 5
NOAA puts the median frost-free season at 179 days, and the season without a hard freeze (28°F) at 212 days.
A hard freeze (28°F) comes after April 2 in half of springs and before October 31 in half of autumns.
The USDA's 2023 Plant Hardiness Zone Map puts Boise in zone 7a across its 8 ZIP code areas (7a in 83709, the largest). By the map's own method, the average of each year's coldest night over 1991-2020, Boise's NOAA station is in zone 7b: the coldest night of a typical year reaches 5°F (30 complete years); the map interpolates between stations and terrain, so the station and the ZIP area can differ by half a zone.
Frost dates for every NOAA station in Idaho · Frost dates by ZIP code
Source: NOAA NCEI 1991-2020 annual normals (frost probabilities), station USW00024131; USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; the station zone: ACIS daily lows, 1991-2020. A 10% date means one year in ten has a frost after it in spring or before it in autumn.
What hardiness zone is each Boise ZIP code in?
The USDA's 2023 map gives each ZIP code area one zone. Boise's 8 ZIP code areas are all in zone 7a. Each ZIP's frost dates are in the frost tool.
Source: USDA 2023 Plant Hardiness Zone Map, ZIP listings: PRISM Group, Oregon State University, https://prism.oregonstate.edu, accessed October 8, 2026; ZIP areas in the place: Census Bureau 2020 ZCTA-to-place relationship file. A ZIP area counts when at least a tenth of its land (and 0.5 km²) lies in the place.
How hot and how cold does it get in Boise?
In a normal year in Boise, 55 days a year reach 90°F (9 of them 100°F or more), 108 nights fall to 32°F or colder and 89 days bring measurable precipitation.
- Days at 90°F or more
- 55a normal year
- Days at 100°F or more
- 9a normal year
- Nights at 32°F or colder
- 108a normal year
- Days that stay below freezing
- 16high of 32°F or less
- Days with 0.01 inch of precipitation
- 89a normal year
- Days with 1 inch of snow or more
- 6a normal year
The highest temperature in Boise's official record (kept by the National Weather Service since 1875) is 111°F, on July 12, 1898; the lowest is −28°F, on January 16, 1888.
The wettest calendar year on that record is 1896, with 22.97 in; the snowiest season is 1916–17, with 50.0 inches.
Source: NOAA NCEI 1991-2020 annual normals, station USW00024131; records: ACIS (NOAA Regional Climate Centers), NWS threaded record BOIthr. Records use complete months only; a month missing more than three days is left out.
How humid and windy is Boise, and how clear are its skies?
The summer (June-August) dew point averages 42°F. The muggiest month is July, with an average dew point of 43°F; the driest air comes in December (23°F). March is the windiest month (8.7 mph on average), and July has the most clear or nearly clear hours (93%).
| Month | Dew point | Humidity | Afternoon humidity | Wind | Clear or few clouds | Overcast |
|---|---|---|---|---|---|---|
| January | 26°F | 73% | 58% | 6.8 mph | 50% | 37% |
| February | 27°F | 62% | 45% | 8.2 mph | 53% | 31% |
| March | 30°F | 53% | 36% | 8.7 mph | 59% | 23% |
| April | 34°F | 47% | 30% | 8.6 mph | 69% | 17% |
| May | 41°F | 45% | 28% | 8.0 mph | 73% | 13% |
| June | 43°F | 36% | 20% | 7.6 mph | 90% | 3% |
| July | 43°F | 30% | 18% | 7.2 mph | 93% | 2% |
| August | 40°F | 33% | 20% | 7.0 mph | 91% | 3% |
| September | 36°F | 41% | 26% | 7.0 mph | 84% | 8% |
| October | 31°F | 58% | 39% | 6.7 mph | 67% | 22% |
| November | 26°F | 72% | 59% | 7.0 mph | 53% | 35% |
| December | 23°F | 76% | 65% | 6.6 mph | 46% | 42% |
Source: NOAA NCEI 1991-2020 hourly normals, station USW00024131. Monthly averages of all hours; afternoon humidity at 3 p.m. local standard time; sky as the share of hours NOAA's observations rate clear or few clouds (a dash where NOAA publishes no sky value).
How sunny is Boise?
Over a year 82% of the sunlight that would reach the ground under clear skies gets through the clouds in the area around Boise, 4.6 kWh per square metre a day. July is the sunniest month (92%) and December the cloudiest (62%). Among the 459 U.S. places of 50,000 or more, that ranks tied 99th (with 11 others) in sunshine.
| Month | Share of clear-sky sunshine | Sunshine, kWh/m² a day |
|---|---|---|
| January | 64% | 1.7 |
| February | 70% | 2.7 |
| March | 72% | 4.0 |
| April | 77% | 5.5 |
| May | 81% | 6.7 |
| June | 86% | 7.5 |
| July | 92% | 7.7 |
| August | 92% | 6.7 |
| September | 89% | 5.2 |
| October | 82% | 3.5 |
| November | 71% | 2.1 |
| December | 62% | 1.4 |
Source: NASA POWER solar climatology, 2001-2020 (CERES SYN1deg). Satellite-based, for the 1-degree cell (about 100 km across) around the station, so it describes the area rather than the airport.
How much heating and cooling does Boise need?
A normal year in Boise brings 5,321 heating degree days, 1% fewer than the median U.S. place (5,373), and 1,045 cooling degree days, 15% more than the median (908). Seven months need 300 or more heating degree days, a monthly mean of about 55°F or colder. For gardens and crops, NOAA counts 3,290 growing degree days a year above 50°F.
| Month | Heating | Cooling |
|---|---|---|
| January | 1,018 | 0 |
| February | 770 | 0 |
| March | 614 | 0 |
| April | 424 | 3 |
| May | 200 | 42 |
| June | 61 | 143 |
| July | 5 | 386 |
| August | 8 | 341 |
| September | 80 | 119 |
| October | 377 | 10 |
| November | 742 | 0 |
| December | 1,020 | 0 |
| Year (annual) | 5,321 | 1,045 |
Source: NOAA NCEI 1991-2020 monthly normals, station USW00024131. A degree day is one degree of a day's mean temperature below 65°F (heating) or above it (cooling); utilities use them to estimate energy use.
Has Boise been warmer than normal lately?
2025 averaged 55.4°F, 2.2°F above the 1991-2020 normal of 53.2°F. 4 of the 5 complete years since 2021 ran warmer than the normal.
| Year | Mean | Against normal | Precip. | Snow |
|---|---|---|---|---|
| 2021 | 55.1°F | +1.9°F | 12.24 | 30.2 |
| 2022 | 52.6°F | −0.6°F | 11.62 | 19.6 |
| 2023 | 54.5°F | +1.3°F | 13.79 | 22.4 |
| 2024 | 55.4°F | +2.2°F | 15.63 | 33.0 |
| 2025 | 55.4°F | +2.2°F | 12.35 | 13.7 |
Over 152 complete years from 1865 to 2025, the station's annual mean temperature rose at a fitted 1.9°F per century (+0.11°C per decade). A fitted rate summarizes the whole record; single years swing well above and below it.
Source: observed years: ACIS, station USW00024131; trend: NOAA GHCN-Monthly v4. A year counts only with all twelve months complete.
How does Boise's climate compare?
Boise is warmer than 80 of the other 84 places with their own NOAA record in Idaho, and wetter than 28. Across the 7,247 U.S. stations with normals, its annual mean of 53.2°F is warmer than 54%.
In the Köppen classification computed from these normals, Boise is BSk: cold semi-arid steppe. What the classes mean.
Places with the most similar year elsewhere
Measured month by month on the normal high, low and precipitation, among places of 20,000 or more people in other states:
Source: NOAA NCEI 1991-2020 normals for every station PlainClimate covers. Similarity: the root-mean-square difference of the 36 monthly figures, precipitation weighted so an inch counts like 6°F.
Which places near Boise share this climate record?
4 places have no NOAA station with 1991-2020 normals of their own, and this station is the nearest full record. A place's own climate can differ from these figures, by several degrees where it sits much higher or lower than the station, nearer the coast, or inside a large city's heat; for the larger places the next nearest records are named with their yearly mean, so the spread around them is visible, and places of 50,000 or more have their own page with NOAA's gridded normals.
- Meridian, IDalso near: Nampa (9 mi, 52.0°F a year); Emmett (17 mi, 51.5°F a year)139,740 people · 9 mi W
- Kuna, ID29,127 people · 9 mi W
- Garden City, ID12,936 people · 8 mi N
- Hidden Springs, ID3,490 people · 10 mi N
Source: Census Bureau 2024 Gazetteer (place centers) and Vintage 2024 population estimates. Distance and direction from the station to each place's center.
What do Boise's other NOAA stations record?
2 more NOAA stations keep 1991-2020 normals in or near Boise. This page uses Boise Air Terminal; the others differ by site and elevation, and the linked ones have pages of their own:
| Station | From the center | Elevation | Year | Jan low | Jul high | Precip. | Snow | Last frost |
|---|---|---|---|---|---|---|---|---|
| Boise Lucky Peak Dam USC00101018 | 10 mi SE | 2,840 ft | 52.8°F | 26°F | 93°F | 15.1 | – | April 30 |
| Boise (7 mi N) USC00101017 | 10 mi N | 3,885 ft | 49.8°F | 24°F | 88°F | 18.0 | 57 | May 17 |
Source: NOAA NCEI 1991-2020 normals for each station. Last frost: the median last spring date of 32°F.
Questions about Boise's climate
What is the coldest month in Boise?
December, with a normal high of 39°F and a normal low of 25°F. The warmest is July (93°F by day, 62°F at night).
Does it snow in Boise?
Yes: 18 inches in a normal year, falling on 18 days with 0.1 inch or more, the most in December (5.6 inches).
What is the rainiest month in Boise?
December, with 1.54 in of precipitation in a normal year; the driest is August with 0.17 in.
What plant hardiness zone is Boise in?
The USDA's 2023 map puts Boise in zone 7a across its 8 ZIP code areas (7a in 83709, the largest). By the same method at Boise's NOAA station, the coldest night of a typical year reaches 5°F (30 years, 1991-2020): zone 7b.
How late can frost come in Boise?
In half of years the last 32°F night comes after April 24; in one year in ten it comes after May 9. Waiting until May 9 leaves about a one-in-ten chance of a later frost.
Nearby and next
- Boise in OctoberThis month day by day, its records and recent years
- Idaho climateThe statewide normals and every place in the state
- Boise Lucky Peak Dam, ID10 miles from this station, 52.8°F a year
- Arrowrock Dam, ID16 miles from this station, 51.0°F a year
- Nampa, ID17 miles from this station, 52.0°F a year
- Emmett, ID23 miles from this station, 51.5°F a year
- Compare two placesMonth by month, side by side
Download these normals (CSV) · JSON · How these figures are made