USDA Hardiness Zone 5a
Frost Dates for 82609 — Casper, Wyoming
NOAA 1991–2020 normals from Casper 1SW, WY (5,143 ft), under a mile northwest.
Updated
In Casper, the last spring frost (32°F) is around May 12 in half of years and has passed by May 26 in nine years out of ten. The first fall frost comes around October 1, as early as September 18 one year in ten, leaving a typical freeze-free season of 143 days (NOAA, Casper 1SW, WY).
- Last spring frost
- May 12
- First fall frost
- October 1
- Growing season
- 143 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
- October 25
- Last snow
- April 28
- Winters with snow
- 100%
- Snow per year
- —
median, 1991–2020
median, 1991–2020
17 of 17 observed
NOAA normal
Frost risk by date in Casper
Half of springs at Casper 1SW, WY see their last 32°F night by May 12; only one in ten is past it by April 28, and one in ten still has one after May 26. Planting tender crops after May 18 leaves a 30% risk of a frost on them, after May 22 20%, and after May 26 10%. The 14 days between the even-odds date and the one-in-ten date is narrower than at 58% of the 33 Wyoming stations behind this site's ZIP pages.
In fall the first 32°F night comes by October 1 in half of years, as early as September 18 one year in ten, and holds off past October 19 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 14, 12 days before the 32°F one. The freeze-free season lasts 143 days in a typical year, longer than at 91% of the 33 Wyoming stations; it reaches 163 days one year in ten and falls short of 123 one year in ten. On average 156 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 12 days longer, to about May 24, and return around September 23. Severe cold of 16°F or below comes every winter, usually between November 11 and March 22.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 11 | May 16 | May 19 | May 22 | May 24 | May 27 | May 30 | Jun 1 | Jun 5 |
| 32°F | Apr 28 | May 2 | May 5 | May 9 | May 12 | May 15 | May 18 | May 22 | May 26 |
| 28°F | Apr 13 | Apr 18 | Apr 22 | Apr 27 | Apr 30 | May 2 | May 5 | May 9 | May 14 |
| 24°F | Mar 29 | Apr 3 | Apr 8 | Apr 12 | Apr 15 | Apr 19 | Apr 23 | Apr 27 | May 1 |
| 20°F | Mar 13 | Mar 21 | Mar 27 | Mar 31 | Apr 3 | Apr 7 | Apr 11 | Apr 16 | Apr 22 |
| 16°F | Mar 2 | Mar 8 | Mar 12 | Mar 18 | Mar 22 | Mar 28 | Apr 1 | Apr 6 | Apr 12 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 10 | Sep 15 | Sep 18 | Sep 21 | Sep 23 | Sep 26 | Sep 28 | Oct 1 | Oct 6 |
| 32°F | Sep 18 | Sep 23 | Sep 27 | Sep 30 | Oct 1 | Oct 5 | Oct 8 | Oct 13 | Oct 19 |
| 28°F | Sep 27 | Oct 2 | Oct 6 | Oct 10 | Oct 13 | Oct 16 | Oct 19 | Oct 23 | Oct 28 |
| 24°F | Oct 5 | Oct 12 | Oct 15 | Oct 18 | Oct 22 | Oct 26 | Oct 29 | Nov 2 | Nov 8 |
| 20°F | Oct 15 | Oct 20 | Oct 25 | Oct 29 | Nov 1 | Nov 4 | Nov 8 | Nov 12 | Nov 19 |
| 16°F | Oct 24 | Oct 30 | Nov 3 | Nov 6 | Nov 11 | Nov 14 | Nov 19 | Nov 23 | Nov 27 |
Freeze probabilities 1991–2020 at Casper 1SW, 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 82609 →Compare Casper with another place →
Compared with the next station
The nearest other station, Casper Wwtp, WY, 2 miles northwest of Casper, has a last frost 2 days earlier (May 10), a first frost 2 days earlier (September 29), a season 5 days shorter.
When it snows in Casper, Wyoming
The first measurable snow (0.1 inch or more) in Casper usually arrives around October 25, and the last of the season around April 28. Those are the middle dates across the winters of 1991–2020 at Casper 1SW, WY, 0.8 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 14 days after the last snow.
Planting calendar for 82609
| When | What to do |
|---|---|
| March 3 – March 17 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 17 – March 31 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 14 – April 28 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 12 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 82609 is under a mile from Casper 1SW, WY, which stands at 5,143 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 82609 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.