Frost dates in Boise City, Idaho
NOAA 1991–2020 normals for a 32 °F freeze. Low spots and the edge of town run colder than downtown.
Short answer
The average last spring frost in Boise City is April 24, and the average first fall frost is October 21, from NOAA's Boise Air Terminal station, 2 miles from the middle of Boise City. 1 year in 10 the last frost comes after May 9, and the first one by October 5. That leaves about 180 frost-free days. Boise City is in USDA planting zone 7a.
Weather stations around Boise City
The first row is the date most people in Boise City go by. The others show how far the dates move across the area.
| Station | Last spring frost | First fall frost | Frost-free |
|---|---|---|---|
| Boise Air Terminal 2 mi away, 2,814 ft | April 24 1 in 10 after May 9 | October 21 1 in 10 by October 5 | 180 days |
| Boise 7 N 10 mi away, 3,885 ft | May 17 1 in 10 after June 10 | October 12 1 in 10 by September 27 | 148 days |
| Boise Lucky Peak Dam 10 mi away, 2,840 ft | April 30 1 in 10 after May 18 | October 22 1 in 10 by September 30 | 175 days |
| Arrowrock Dam 15 mi away, 3,235 ft | April 28 1 in 10 after May 16 | October 14 1 in 10 by October 1 | 169 days |
| Nampa Sugar Factory 17 mi away, 2,470 ft | April 29 1 in 10 after May 18 | October 13 1 in 10 by September 29 | 167 days |
Distances are from the middle of Boise City as the Census Bureau maps it. The average date is NOAA's 50% date: half of years have a later last frost, or an earlier first one. Plan by the 1-in-10 date if a freeze would cost you plants. The planting zone is the USDA 2023 zone for ZIP code 83706, at the middle of the city.
Your exact ZIP code
Boise City covers a lot of ground. For the station nearest your own street, and its planting zone, type your ZIP code.
How these dates work
Frost dates come from NOAA's 1991 to 2020 Climate Normals, which work out from each weather station's daily lows how likely the last spring freeze and the first fall freeze (32 °F) are by each date. We use the station nearest the middle of your ZIP code and show its height and distance, since a station on a hill or by a lake can differ from your yard.
The average date is the 50% date: half of years have a freeze after the spring date or before the fall one. The 1-in-10 dates are NOAA's 10% dates, the ones to plan by if a late freeze would cost you plants. Within one yard, cold air pools in low spots while walls and paving hold heat, so some corners freeze before others.
More frost dates
All of Idaho, station by station.
Other Idaho cities: Meridian
Nearby: Spokane, WA · Salt Lake City, UT · Reno, NV
Where the numbers come from
- USDA Plant Hardiness Zone Map, 2023. Agricultural Research Service, U.S. Department of Agriculture
- PRISM Climate Group, Oregon State University (zone data)
- NOAA NCEI, U.S. Climate Normals 1991–2020, annual/seasonal
- NOAA, Normals calculation methodology (frost-freeze probability dates)
- US Census Bureau, 2025 ZCTA gazetteer (ZIP code centers)
- US Census Bureau, 2025 city population estimates and place gazetteer