USDA Hardiness Zone 5a
Frost Dates for 82435 — Powell, Wyoming
NOAA 1991–2020 normals from Powell Field Stn, WY (4,372 ft), 5 miles east.
Updated
In Powell, the last spring frost (32°F) is around May 19 in half of years and has passed by June 4 in nine years out of ten. The first fall frost comes around September 20, as early as September 7 one year in ten, leaving a typical freeze-free season of 123 days (NOAA, Powell Field Stn, WY).
- Last spring frost
- May 19
- First fall frost
- September 20
- Growing season
- 123 days
- Hardiness zone
- 5a
50% probability
50% probability
freeze-free, 50%
-20 to -15°F (-28.9 to -26.1°C) coldest night
- First snow
- November 2
- Last snow
- April 5
- Winters with snow
- 100%
- Snow per year
- 11.2"
median, 1991–2020
median, 1991–2020
25 of 25 observed
NOAA normal
Frost risk by date in Powell
Half of springs at Powell Field Stn, WY see their last 32°F night by May 19; only one in ten is past it by May 5, and one in ten still has one after June 4. Planting tender crops after May 26 leaves a 30% risk of a frost on them, after May 29 20%, and after June 4 10%. The 16 days between the even-odds date and the one-in-ten date is wider than at 55% of the 33 Wyoming stations behind this site's ZIP pages.
In fall the first 32°F night comes by September 20 in half of years, as early as September 7 one year in ten, and holds off past October 1 one year in ten. A hard freeze of 28°F follows 9 days later, around September 29; in spring the one-in-ten date for 28°F is May 20, 15 days before the 32°F one. The freeze-free season lasts 123 days in a typical year, shorter than at 52% of the 33 Wyoming stations; it reaches 141 days one year in ten and falls short of 102 one year in ten. On average 191 nights a year drop to 32°F or below. Severe cold of 16°F or below comes every winter, usually between October 29 and April 6.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | too rare for a date | ||||||||
| 32°F | May 5 | May 9 | May 13 | May 16 | May 19 | May 23 | May 26 | May 29 | Jun 4 |
| 28°F | Apr 25 | Apr 29 | Apr 30 | May 3 | May 5 | May 7 | May 10 | May 14 | May 20 |
| 24°F | Apr 11 | Apr 16 | Apr 20 | Apr 23 | Apr 25 | Apr 28 | Apr 30 | May 3 | May 7 |
| 20°F | Apr 1 | Apr 6 | Apr 9 | Apr 13 | Apr 16 | Apr 18 | Apr 22 | Apr 25 | Apr 29 |
| 16°F | Mar 20 | Mar 28 | Mar 31 | Apr 3 | Apr 6 | Apr 9 | Apr 13 | Apr 16 | Apr 22 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | too rare for a date | ||||||||
| 32°F | Sep 7 | Sep 12 | Sep 15 | Sep 17 | Sep 20 | Sep 22 | Sep 24 | Sep 27 | Oct 1 |
| 28°F | Sep 16 | Sep 21 | Sep 24 | Sep 27 | Sep 29 | Oct 2 | Oct 4 | Oct 8 | Oct 14 |
| 24°F | Sep 26 | Oct 1 | Oct 3 | Oct 6 | Oct 10 | Oct 14 | Oct 17 | Oct 20 | Oct 25 |
| 20°F | Oct 5 | Oct 11 | Oct 14 | Oct 17 | Oct 20 | Oct 23 | Oct 26 | Oct 30 | Nov 3 |
| 16°F | Oct 13 | Oct 19 | Oct 22 | Oct 26 | Oct 29 | Nov 1 | Nov 3 | Nov 7 | Nov 12 |
Freeze probabilities 1991–2020 at Powell Field Stn, 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 82435 →Compare Powell with another place →
Weather by month in Powell
July is the warmest month at Powell Field Stn, WY, averaging 85°F by day and 52°F at night; January is the coldest at 32°F and 6°F. A freezing night is all but certain in every month from October to May (a 90% chance or more). From July to August the chance of a 32°F night stays under 10% each month. In spring, June still brings one in 12% of years.
Warmth for growing adds up to 1,934 growing degree days a year (base 50°F), fewer than at 70% of the 33 Wyoming stations. 28% of them (547) have built up by the end of June, and July adds the most, 583. Precipitation totals 6.8 inches a year, most in June (1.3") and least in December (0.1"); May to September bring 66% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 32 | 6 | 0.2 | 100% | 31 | 0 |
| Feb | 36 | 10 | 0.2 | 100% | 28 | 0 |
| Mar | 48 | 20 | 0.3 | 100% | 28 | 4 |
| Apr | 57 | 28 | 0.6 | 100% | 19 | 30 |
| May | 66 | 40 | 1.2 | 97% | 5 | 159 |
| Jun | 76 | 47 | 1.3 | 12% | <1 | 354 |
| Jul | 85 | 52 | 0.8 | 2% | <1 | 583 |
| Aug | 84 | 50 | 0.4 | 2% | 0 | 519 |
| Sep | 73 | 41 | 0.8 | 87% | 3 | 241 |
| Oct | 58 | 29 | 0.7 | 100% | 19 | 42 |
| Nov | 43 | 17 | 0.2 | 100% | 29 | 1 |
| Dec | 33 | 8 | 0.1 | 100% | 31 | 0 |
Monthly normals 1991–2020 at Powell Field Stn, WY (4,372 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, Lovell, WY, 23 miles east of Powell and 525 feet lower, has a last frost 10 days earlier (May 9), a first frost 9 days later (September 29), a season 19 days longer.
When it snows in Powell, Wyoming
The first measurable snow (0.1 inch or more) in Powell usually arrives around November 2, and the last of the season around April 5. Those are the middle dates across the winters of 1991–2020 at Powell Field Stn, WY, 5.4 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 44 days after the last snow.
Planting calendar for 82435
| When | What to do |
|---|---|
| March 10 – March 24 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 24 – April 7 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 21 – May 5 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 19 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by June 28 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 6 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| September 20 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 82435 is 5 miles from Powell Field Stn, WY, which stands at 4,372 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 82435 in zone 5a, the band where the coldest night of the year averaged -20 to -15°F (-28.9 to -26.1°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.