USDA Hardiness Zone 5b
Frost Dates for 83110 — Afton, Wyoming
NOAA 1991–2020 normals from Afton, WY (6,248 ft), 4 miles north.
Updated
In Afton, the last spring frost (32°F) is around June 20 in half of years and has passed by July 7 in nine years out of ten. The first fall frost comes around September 1, as early as August 12 one year in ten, leaving a typical freeze-free season of 71 days (NOAA, Afton, WY).
- Last spring frost
- June 20
- First fall frost
- September 1
- Growing season
- 71 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
- October 16
- Last snow
- May 6
- Winters with snow
- 100%
- Snow per year
- 87.8"
median, 1991–2020
median, 1991–2020
27 of 27 observed
NOAA normal
Frost risk by date in Afton
Half of springs at Afton, WY see their last 32°F night by June 20; only one in ten is past it by June 2, and one in ten still has one after July 7. Planting tender crops after June 27 leaves a 30% risk of a frost on them, after July 1 20%, and after July 7 10%. The 17 days between the even-odds date and the one-in-ten date is wider than at 73% of the 33 Wyoming stations behind this site's ZIP pages.
In fall the first 32°F night comes by September 1 in half of years, as early as August 12 one year in ten, and holds off past September 15 one year in ten. A hard freeze of 28°F follows 12 days later, around September 13; in spring the one-in-ten date for 28°F is June 20, 17 days before the 32°F one. The freeze-free season lasts 71 days in a typical year, shorter than at 97% of the 33 Wyoming stations; it reaches 93 days one year in ten and falls short of 49 one year in ten. On average 227 nights a year drop to 32°F or below. Severe cold of 16°F or below comes every winter, usually between October 23 and April 8.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | too rare for a date | ||||||||
| 32°F | Jun 2 | Jun 10 | Jun 14 | Jun 17 | Jun 20 | Jun 24 | Jun 27 | Jul 1 | Jul 7 |
| 28°F | May 10 | May 16 | May 22 | May 28 | Jun 1 | Jun 5 | Jun 9 | Jun 14 | Jun 20 |
| 24°F | Apr 24 | Apr 29 | May 2 | May 5 | May 9 | May 12 | May 16 | May 22 | May 30 |
| 20°F | Apr 8 | Apr 13 | Apr 17 | Apr 20 | Apr 24 | Apr 27 | Apr 30 | May 4 | May 10 |
| 16°F | Mar 27 | Mar 31 | Apr 3 | Apr 6 | Apr 8 | Apr 12 | Apr 15 | Apr 19 | Apr 26 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | too rare for a date | ||||||||
| 32°F | Aug 12 | Aug 20 | Aug 27 | Aug 30 | Sep 1 | Sep 4 | Sep 8 | Sep 11 | Sep 15 |
| 28°F | Aug 29 | Sep 3 | Sep 7 | Sep 10 | Sep 13 | Sep 16 | Sep 19 | Sep 22 | Sep 27 |
| 24°F | Sep 12 | Sep 17 | Sep 20 | Sep 23 | Sep 27 | Sep 29 | Oct 2 | Oct 6 | Oct 12 |
| 20°F | Sep 24 | Sep 29 | Oct 2 | Oct 6 | Oct 10 | Oct 14 | Oct 17 | Oct 21 | Oct 25 |
| 16°F | Oct 7 | Oct 13 | Oct 17 | Oct 20 | Oct 23 | Oct 26 | Oct 29 | Nov 1 | Nov 6 |
Freeze probabilities 1991–2020 at Afton, WY, 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 83110 →Compare Afton with another place →
Weather by month in Afton
July is the warmest month at Afton, WY, averaging 80°F by day and 44°F at night; January is the coldest at 26°F and 5°F. A freezing night is all but certain in every month from September to May (a 90% chance or more). No month is safe from a 32°F night: even the warmest has at least a 10% chance. In spring, June still brings one in 90% of years and July still brings one in 21% of years.
Warmth for growing adds up to 1,061 growing degree days a year (base 50°F), the fewest of the 33 Wyoming stations. 20% of them (215) have built up by the end of June, and July adds the most, 376. Precipitation totals 17.8 inches a year, most in May (2.4") and least in July (1.1"); May to September bring 44% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 26 | 5 | 1.3 | 100% | 31 | 0 |
| Feb | 31 | 8 | 1.3 | 100% | 28 | 0 |
| Mar | 40 | 17 | 1.5 | 100% | 30 | 0 |
| Apr | 50 | 25 | 1.5 | 100% | 26 | 3 |
| May | 60 | 33 | 2.4 | 100% | 13 | 43 |
| Jun | 71 | 38 | 1.8 | 90% | 4 | 169 |
| Jul | 80 | 44 | 1.1 | 21% | 1 | 376 |
| Aug | 79 | 43 | 1.1 | 44% | 1 | 343 |
| Sep | 69 | 34 | 1.5 | 100% | 9 | 117 |
| Oct | 56 | 26 | 1.6 | 100% | 25 | 11 |
| Nov | 39 | 16 | 1.3 | 100% | 29 | 0 |
| Dec | 27 | 7 | 1.4 | 100% | 31 | 0 |
Monthly normals 1991–2020 at Afton, WY (6,248 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, Bern, ID, 34 miles southwest of Afton and 284 feet lower, has a last frost 3 days earlier (June 17), a first frost 2 days later (September 3), a season 6 days longer.
When it snows in Afton, Wyoming
The first measurable snow (0.1 inch or more) in Afton usually arrives around October 16, and the last of the season around May 6. Those are the middle dates across the winters of 1991–2020 at Afton, WY, 3.6 miles away: half of years saw snow earlier, half later. Every one of those winters saw snow. The last 32°F night of spring typically comes 45 days after the last snow.
Planting calendar for 83110
| When | What to do |
|---|---|
| April 11 – April 25 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| April 25 – May 9 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| May 23 – June 6 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| June 20 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by June 9 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by August 18 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| September 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 83110 is 4 miles from Afton, WY, which stands at 6,248 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station. The 2023 USDA Plant Hardiness Zone Map lists ZIP 83110 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.