USDA Hardiness Zone 5b
Frost Dates for 83442 — Rigby, Idaho
NOAA 1991–2020 normals from Rigby, ID (4,856 ft), 2 miles west.
Updated
In Rigby, the last spring frost (32°F) is around May 9 in half of years and has passed by May 25 in nine years out of ten. The first fall frost comes around October 5, as early as September 21 one year in ten, leaving a typical freeze-free season of 148 days (NOAA, Rigby, ID).
- Last spring frost
- May 9
- First fall frost
- October 5
- Growing season
- 148 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 9
- Last snow
- April 3
- Winters with snow
- 93%
- Snow per year
- —
median, 1991–2020
median, 1991–2020
14 of 15 observed
NOAA normal
Frost risk by date in Rigby
Half of springs at Rigby, 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 May 25. Planting tender crops after May 15 leaves a 30% risk of a frost on them, after May 19 20%, and after May 25 10%. The 16 days between the even-odds date and the one-in-ten date is narrower than at 66% of the 67 Idaho stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 5 in half of years, as early as September 21 one year in ten, and holds off past October 18 one year in ten. A hard freeze of 28°F follows 11 days later, around October 16; in spring the one-in-ten date for 28°F is May 11, 14 days before the 32°F one. The freeze-free season lasts 148 days in a typical year, shorter than at 51% of the 67 Idaho stations; it reaches 167 days one year in ten and falls short of 125 one year in ten. On average 163 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 17 days longer, to about May 26, and return around September 24. Severe cold of 16°F or below comes every winter, usually between November 14 and March 9.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 10 | May 16 | May 19 | May 23 | May 26 | May 31 | Jun 4 | Jun 8 | Jun 14 |
| 32°F | Apr 27 | May 1 | May 3 | May 6 | May 9 | May 12 | May 15 | May 19 | May 25 |
| 28°F | Apr 12 | Apr 17 | Apr 21 | Apr 24 | Apr 28 | Apr 30 | May 2 | May 6 | May 11 |
| 24°F | Mar 24 | Apr 1 | Apr 6 | Apr 9 | Apr 13 | Apr 16 | Apr 19 | Apr 25 | Apr 30 |
| 20°F | Mar 8 | Mar 13 | Mar 17 | Mar 24 | Mar 30 | Apr 2 | Apr 6 | Apr 11 | Apr 17 |
| 16°F | Feb 27 | Mar 2 | Mar 5 | Mar 7 | Mar 9 | Mar 13 | Mar 16 | Mar 24 | Apr 1 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 9 | Sep 14 | Sep 19 | Sep 21 | Sep 24 | Sep 27 | Sep 30 | Oct 3 | Oct 6 |
| 32°F | Sep 21 | Sep 27 | Sep 30 | Oct 2 | Oct 5 | Oct 6 | Oct 10 | Oct 14 | Oct 18 |
| 28°F | Oct 2 | Oct 6 | Oct 9 | Oct 13 | Oct 16 | Oct 18 | Oct 21 | Oct 25 | Oct 28 |
| 24°F | Oct 11 | Oct 16 | Oct 20 | Oct 23 | Oct 25 | Oct 28 | Oct 31 | Nov 3 | Nov 9 |
| 20°F | Oct 21 | Oct 25 | Oct 29 | Nov 1 | Nov 4 | Nov 7 | Nov 11 | Nov 15 | Nov 21 |
| 16°F | Oct 29 | Nov 3 | Nov 6 | Nov 11 | Nov 14 | Nov 18 | Nov 22 | Nov 25 | Nov 29 |
Freeze probabilities 1991–2020 at Rigby, 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 83442 →Compare Rigby with another place →
Frost risk through the year in Rigby
In Rigby, the spring curve drops under 10% on May 25 and the fall curve passes 10% on September 21, 119 days later; that gap is longer than at 54% of the 67 Idaho stations with frost dates. The spring risk falls from 90% to 10% over 28 days (April 27 to May 25) and the fall risk climbs from 10% to 90% over 27 days (September 21 to October 18): both ends of the season vary about as much. At Rexburg Byu Idaho, ID, 10 miles northeast, the same gap runs from June 2 to September 6, 23 days shorter.
| Planted on | Another 32°F night | 28°F night |
|---|---|---|
| Apr 25 | over 90% | 58% |
| May 2 | 75% | 30% |
| May 950% date | 50% | 14% |
| May 16 | 28% | under 10% |
| May 23 | 13% | under 10% |
| May 30 | under 10% | under 10% |
Weather by month in Rigby
July is the warmest month at Rigby, ID, averaging 85°F by day and 55°F at night; December 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 June to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 80% of years.
Warmth for growing adds up to 2,145 growing degree days a year (base 50°F), fewer than at 54% of the 67 Idaho stations. 26% of them (554) have built up by the end of June, and July adds the most, 606.
| Month | High °F | Low °F | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|
| Jan | 31 | 15 | 100% | 31 | 0 |
| Feb | 35 | 18 | 100% | 26 | 0 |
| Mar | 48 | 28 | 100% | 23 | 5 |
| Apr | 57 | 33 | 100% | 14 | 28 |
| May | 67 | 42 | 80% | 4 | 169 |
| Jun | 75 | 48 | 4% | <1 | 352 |
| Jul | 85 | 55 | 0% | 0 | 606 |
| Aug | 84 | 54 | 0% | 0 | 586 |
| Sep | 75 | 46 | 34% | 1 | 327 |
| Oct | 60 | 35 | 99% | 12 | 70 |
| Nov | 43 | 25 | 100% | 23 | 3 |
| Dec | 30 | 16 | 100% | 30 | 0 |
Monthly normals 1991–2020 at Rigby, ID (4,856 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, Rexburg Byu Idaho, ID, 10 miles northeast of Rigby, has a last frost 3 days later (May 12), a first frost 11 days earlier (September 24), a season 16 days shorter.
When it snows in Rigby, Idaho
The first measurable snow (0.1 inch or more) in Rigby usually arrives around November 9, and the last of the season around April 3. Those are the middle dates across the winters of 1991–2020 at Rexburg Byu Idaho, ID, 10.1 miles away: half of years saw snow earlier, half later. Snow fell in 93% of those winters. The last 32°F night of spring typically comes 36 days after the last snow.
Planting calendar for 83442
| 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 13 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 21 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| October 5 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 83442 is 2 miles from Rigby, ID, which stands at 4,856 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 83442 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.