USDA Hardiness Zone 5b
Frost Dates for 83401 — Idaho Falls, Idaho
NOAA 1991–2020 normals from Idaho Falls - Kifi, ID (4,742 ft), 2 miles southwest.
Updated
In Idaho Falls, the last spring frost (32°F) is around May 9 in half of years and has passed by June 2 in nine years out of ten. The first fall frost comes around October 1, as early as September 17 one year in ten, leaving a typical freeze-free season of 142 days (NOAA, Idaho Falls - Kifi, ID).
- Last spring frost
- May 9
- First fall frost
- October 1
- Growing season
- 142 days
- Hardiness zone
- 5b
50% probability
50% probability
freeze-free, 50%
-15 to -10°F (-26.1 to -23.3°C) coldest night
- First snow
- November 6
- Last snow
- March 30
- Winters with snow
- 92%
- Snow per year
- —
median, 1991–2020
median, 1991–2020
24 of 26 observed
NOAA normal
Frost risk by date in Idaho Falls
Half of springs at Idaho Falls - Kifi, ID see their last 32°F night by May 9; only one in ten is past it by April 27, and one in ten still has one after June 2. Planting tender crops after May 17 leaves a 30% risk of a frost on them, after May 23 20%, and after June 2 10%. The 24 days between the even-odds date and the one-in-ten date is wider than at 93% of the 67 Idaho stations behind this site's ZIP pages, so a fixed calendar date is a gamble here.
In fall the first 32°F night comes by October 1 in half of years, as early as September 17 one year in ten, and holds off past October 15 one year in ten. A hard freeze of 28°F follows 12 days later, around October 13; in spring the one-in-ten date for 28°F is May 11, 22 days before the 32°F one. The freeze-free season lasts 142 days in a typical year, shorter than at 58% of the 67 Idaho stations; it reaches 163 days one year in ten and falls short of 117 one year in ten. On average 166 nights a year drop to 32°F or below. Nights of 36°F, when frost can still settle on leaves in low, open spots, continue 21 days longer, to about May 30, and return around September 20. Severe cold of 16°F or below comes every winter, usually between November 12 and March 6.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 10 | May 16 | May 19 | May 24 | May 30 | Jun 3 | Jun 7 | Jun 11 | Jun 16 |
| 32°F | Apr 27 | May 1 | May 4 | May 7 | May 9 | May 13 | May 17 | May 23 | Jun 2 |
| 28°F | Apr 11 | Apr 17 | Apr 21 | Apr 24 | Apr 28 | Apr 30 | May 3 | May 6 | May 11 |
| 24°F | Mar 20 | Mar 28 | Apr 3 | Apr 7 | Apr 11 | Apr 15 | Apr 19 | Apr 24 | Apr 29 |
| 20°F | Mar 4 | Mar 8 | Mar 11 | Mar 16 | Mar 22 | Mar 28 | Apr 2 | Apr 7 | Apr 15 |
| 16°F | Feb 20 | Feb 27 | Mar 2 | Mar 4 | Mar 6 | Mar 9 | Mar 12 | Mar 17 | Mar 27 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 4 | Sep 9 | Sep 14 | Sep 17 | Sep 20 | Sep 23 | Sep 25 | Sep 29 | Oct 3 |
| 32°F | Sep 17 | Sep 21 | Sep 25 | Sep 28 | Oct 1 | Oct 3 | Oct 6 | Oct 10 | Oct 15 |
| 28°F | Sep 27 | Oct 2 | Oct 6 | Oct 9 | Oct 13 | Oct 16 | Oct 19 | Oct 23 | Oct 27 |
| 24°F | Oct 9 | Oct 14 | Oct 19 | Oct 22 | Oct 25 | Oct 28 | Oct 31 | Nov 3 | Nov 8 |
| 20°F | Oct 20 | Oct 25 | Oct 28 | Nov 1 | Nov 3 | Nov 5 | Nov 9 | Nov 14 | Nov 20 |
| 16°F | Oct 27 | Nov 1 | Nov 5 | Nov 9 | Nov 12 | Nov 16 | Nov 20 | Nov 23 | Nov 28 |
Freeze probabilities 1991–2020 at Idaho Falls - Kifi, ID, from NOAA NCEI U.S. Climate Normals. Where a temperature is reached in fewer than 99.5% of years, the dates describe only the years that reach it. Not a forecast.
Frost risk on any date in 83401 →Compare Idaho Falls with another place →
Weather by month in Idaho Falls
July is the warmest month at Idaho Falls - Kifi, ID, averaging 86°F by day and 55°F at night; January is the coldest at 30°F and 16°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From July to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 78% of years and June still brings one in 12% of years.
Warmth for growing adds up to 2,241 growing degree days a year (base 50°F), more than at 52% of the 67 Idaho stations. 27% of them (614) have built up by the end of June, and July adds the most, 643. Precipitation totals 13.6 inches a year, most in May (1.9") and least in July (0.5"); May to September bring 40% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 30 | 16 | 1.1 | 100% | 30 | 0 |
| Feb | 36 | 20 | 1.0 | 100% | 26 | 0 |
| Mar | 48 | 29 | 1.3 | 100% | 23 | 4 |
| Apr | 58 | 34 | 1.4 | 100% | 14 | 41 |
| May | 67 | 42 | 1.9 | 78% | 3 | 187 |
| Jun | 77 | 49 | 1.3 | 12% | 1 | 383 |
| Jul | 86 | 55 | 0.5 | 0% | 0 | 643 |
| Aug | 86 | 54 | 0.7 | 0% | <1 | 606 |
| Sep | 75 | 45 | 1.1 | 49% | 2 | 315 |
| Oct | 59 | 35 | 1.2 | 99% | 14 | 61 |
| Nov | 43 | 25 | 1.0 | 100% | 25 | 2 |
| Dec | 31 | 17 | 1.1 | 100% | 30 | 0 |
Monthly normals 1991–2020 at Idaho Falls - Kifi, ID (4,742 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
Compared with the next station
The nearest other station, Idaho Falls Fanning Field, ID, 4 miles west of Idaho Falls, has a last frost 14 days later (May 23), a first frost 11 days earlier (September 20), a season 28 days shorter.
When it snows in Idaho Falls, Idaho
The first measurable snow (0.1 inch or more) in Idaho Falls usually arrives around November 6, and the last of the season around March 30. Those are the middle dates across the winters of 1991–2020 at Idaho Falls - Kifi, ID, 1.9 miles away: half of years saw snow earlier, half later. Snow fell in 92% of those winters. The last 32°F night of spring typically comes 40 days after the last snow.
Planting calendar for 83401
| When | What to do |
|---|---|
| February 28 – March 14 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 14 – March 28 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 11 – April 25 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 9 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 9 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 17 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 1 onward | Plant garlic, mulch beds, lift tender bulbsGarlic wants a cold spell; bare soil loses structure over winter. |
The weeks before and after the 50% dates are general rules of thumb, not NOAA figures; a seed packet gives the timing for each variety.
Where these figures come from
ZIP 83401 is 2 miles from Idaho Falls - Kifi, ID, which stands at 4,742 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 2 other ZIP codes share the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 83401 in zone 5b, the band where the coldest night of the year averaged -15 to -10°F (-26.1 to -23.3°C) over 1991–2020; a zone describes winter lows, not frost dates.
Hardiness zone and temperature range: USDA Plant Hardiness Zone Map 2023 (USDA-ARS, Oregon State University), ZIP-code listing, unchanged. °C converted from °F by this site.
Thirty-year averages, not a forecast: check the forecast before planting out. How stations are matched and which pages are offered to search engines: methodology.