When is the last frost in Irwin, ID?

Frost is possible in any month at the nearest NOAA station (Swan Valley, ID), so there is no reliable average last frost date.

When is the first frost in Irwin, ID?

Frost is possible in any month at the nearest NOAA station.

Are these frost dates a forecast?

No. They are 30-year averages and probabilities from NOAA weather station records. Use them to plan, then watch your local forecast before planting tender crops or leaving them uncovered.

Frost dates for 83428Irwin, ID

Frost is possible in any month near Irwin, based on NOAA 1991-2020 records for the Swan Valley, ID station.

Frost is possible in any month. Even summer nights can drop to freezing at this station, so protect tender plants whenever cold nights are forecast.

Frost risk by date

NOAA reports frost dates as probabilities. The middle date is the average (a 50% chance). For spring, the 10% date is a safer planting date: frost after it happens in about 1 year in 10. Light frost (36°F) can damage tender plants; a hard freeze (28°F) kills most annuals.

Spring dates: chance of a frost AFTER the date. Fall dates: chance of a frost BEFORE the date.
Temperature	Last spring: 90% / 50% / 10% chance	First fall: 10% / 50% / 90% chance	Growing season (50%)	Years with at least one
Light frost (36°F)	—	—	40 days	100%
Frost / freeze (32°F)	—	—	69 days	100%
Hard freeze (28°F)	May 7 · May 29 · Jun 21	Aug 30 · Sep 16 · Oct 3	109 days	100%

Where these dates come from

ZIP code 83428 is matched to the NOAA station Swan Valley, ID, 6.1 km away, at 5,397 ft elevation (20 ft higher than the ZIP code's center). Nearby stations for comparison:

Station	Elevation	Avg last frost	Avg first frost
Swan Valley, ID (used)	5,397 ft	—	—
Driggs, ID	6,120 ft	Jun 13	Sep 9
Jackson, WY	6,210 ft	—	—
Idaho Falls 16 Se, ID	5,828 ft	Jun 9	Sep 11

Frost dates near Irwin

Swan Valley, ID 83449 · last —, first —
Ririe, ID 83443 · last Jun 9, first Sep 11
Victor, ID 83455 · last Jun 13, first Sep 9
Alpine, WY 83128 · last —, first —
Wilson, WY 83014 · last —, first —
Driggs, ID 83422 · last Jun 13, first Sep 9
Wayan, ID 83285 · last —, first —
Jackson, WY 83002 · last —, first —

Frequently asked questions

When is the last frost in Irwin, ID?: Frost is possible in any month at the nearest NOAA station (Swan Valley, ID), so there is no reliable average last frost date.
When is the first frost in Irwin, ID?: Frost is possible in any month at the nearest NOAA station.
Are these frost dates a forecast?: No. They are 30-year averages and probabilities from NOAA weather station records. Use them to plan, then watch your local forecast before planting tender crops or leaving them uncovered.