Frost dates / Idaho / Boise City

Frost dates in Boise City, ID

The station on this page is BOISE AIR TERMINAL, ID US (USW00024131), 2.3 miles from the city point. Population in the Census 2024 estimate is 237,963.

Zone 7aUSDA average annual extreme minimum 0°F to 5°F, from ZIP 83706 (1.9 miles from the city point used on this page).

Median last 32°F is April 24. Median first 32°F is October 21. The 50% growing-season length is 179 days. The green band runs from the median last frost to the median first frost. Thin ticks mark the 10%, 50%, and 90% dates.

Outside the median season Growing seasonTicks: 10%, 50%, and 90%

Last 32°F in spring

NCEI’s probability is the chance the last spring minimum of 32°F or lower occurs on or after the date.

Probability	Date	How to read it
90%	April 4	Earlier date. A last 32°F on or after this day is common.
50%	April 24	Median.
10%	May 9	Later date. A last 32°F on or after this day is uncommon.

First 32°F in fall

NCEI’s probability is the chance the first autumn minimum of 32°F or lower occurs on or before the date.

Probability	Date	How to read it
10%	October 5	Earlier date. A first 32°F on or before this day is uncommon.
50%	October 21	Median.
90%	November 5	Later date. A first 32°F on or before this day is common.

32°F growing-season length

Days between the last spring 32°F and the first autumn 32°F. The figure is a length the season meets or exceeds at that probability, from NCEI, not a subtraction done on this site.

Probability the season is at least this long	Days
10%	203
50%	179
90%	156

28°F threshold

	10%	50%	90%
Last, on or after	April 25	April 2	March 10
First, on or before	October 17	October 31	November 19
Season at least	241 days	212 days	186 days

36°F threshold

	10%	50%	90%
Last, on or after	May 29	May 8	April 23
First, on or before	September 25	October 8	October 25
Season at least	173 days	153 days	128 days

Station BOISE AIR TERMINAL, ID US (USW00024131). Completeness flag S, 27 years used for the 32°F dates. NCEI’s annual probability of at least one day at or below 32°F is 100%. Freeze dates are conditional on that threshold occurring. Elevation 857.7 m. The same probability language applies to the 28°F and 36°F rows when those dates passed the same quality checks.

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Boise City, ID

Zone 7aAverage annual extreme minimum 0°F to 5°F

Outside the median season Growing seasonTicks: 10%, 50%, and 90%

Idaho. Nearest qualified station: BOISE AIR TERMINAL, ID US (USW00024131), 2.3 miles. Median last 32°F April 24. Median first 32°F October 21. The 50% growing-season length is 179 days.

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32°F probabilities at this station

	10%	50%	90%
Last 32°F on or after	May 9	April 24	April 4
First 32°F on or before	October 5	October 21	November 5

Column order matches the NCEI file: for the last freeze, 10% is the later date and 90% is the earlier date. How to read the probabilities.

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Planting calendar

Frost dates for Idaho are above. Planting windows appear for states with a cited extension guide. The fall and seed tools use the numbers you enter and the station dates.

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