USDA Hardiness Zone 4b
Frost Dates for 59758 — West Yellowstone, Montana
NOAA 1991–2020 normals from Hebgen Dam, MT (6,489 ft), 12 miles northwest.
Updated
In West Yellowstone, the last spring frost (32°F) is around June 15 in half of years and has passed by July 7 in nine years out of ten. The first fall frost comes around September 10, as early as August 25 one year in ten, leaving a typical freeze-free season of 87 days (NOAA, Hebgen Dam, MT).
- Last spring frost
- June 15
- First fall frost
- September 10
- Growing season
- 87 days
- Hardiness zone
- 4b
50% probability
50% probability
freeze-free, 50%
-25 to -20°F (-31.7 to -28.9°C) coldest night
- First snow
- October 20
- Last snow
- April 20
- Winters with snow
- 100%
- Snow per year
- 177.2"
median, 1991–2020
median, 1991–2020
24 of 24 observed
NOAA normal
Frost risk by date in West Yellowstone
Half of springs at Hebgen Dam, MT see their last 32°F night by June 15; only one in ten is past it by May 29, and one in ten still has one after July 7. Planting tender crops after June 23 leaves a 30% risk of a frost on them, after June 30 20%, and after July 7 10%. The 22 days between the even-odds date and the one-in-ten date is wider than at 93% of the 68 Montana 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 September 10 in half of years, as early as August 25 one year in ten, and holds off past September 27 one year in ten. A hard freeze of 28°F follows 16 days later, around September 26; in spring the one-in-ten date for 28°F is June 16, 21 days before the 32°F one. The freeze-free season lasts 87 days in a typical year, shorter than at 96% of the 68 Montana stations; it reaches 111 days one year in ten and falls short of 59 one year in ten. On average 226 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 20.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | too rare for a date | ||||||||
| 32°F | May 29 | Jun 4 | Jun 7 | Jun 11 | Jun 15 | Jun 19 | Jun 23 | Jun 30 | Jul 7 |
| 28°F | May 8 | May 12 | May 16 | May 20 | May 24 | May 27 | Jun 1 | Jun 7 | Jun 16 |
| 24°F | Apr 27 | May 1 | May 3 | May 5 | May 7 | May 10 | May 13 | May 17 | May 27 |
| 20°F | Apr 15 | Apr 19 | Apr 23 | Apr 26 | Apr 29 | May 1 | May 4 | May 6 | May 10 |
| 16°F | Apr 6 | Apr 10 | Apr 13 | Apr 17 | Apr 20 | Apr 22 | Apr 26 | Apr 29 | May 4 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | too rare for a date | ||||||||
| 32°F | Aug 25 | Sep 1 | Sep 3 | Sep 6 | Sep 10 | Sep 13 | Sep 16 | Sep 20 | Sep 27 |
| 28°F | Sep 10 | Sep 15 | Sep 19 | Sep 23 | Sep 26 | Sep 29 | Oct 2 | Oct 5 | Oct 10 |
| 24°F | Sep 20 | Sep 27 | Oct 1 | Oct 4 | Oct 7 | Oct 11 | Oct 15 | Oct 19 | Oct 24 |
| 20°F | Oct 2 | Oct 6 | Oct 12 | Oct 16 | Oct 20 | Oct 23 | Oct 27 | Nov 1 | Nov 5 |
| 16°F | Oct 11 | Oct 18 | Oct 22 | Oct 26 | Oct 29 | Nov 1 | Nov 4 | Nov 8 | Nov 13 |
Freeze probabilities 1991–2020 at Hebgen Dam, MT, 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 59758 →Compare West Yellowstone with another place →
Weather by month in West Yellowstone
July is the warmest month at Hebgen Dam, MT, averaging 79°F by day and 45°F at night; January is the coldest at 23°F and 4°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 85% of years and July still brings one in 18% of years.
Warmth for growing adds up to 1,017 growing degree days a year (base 50°F), fewer than at 99% of the 68 Montana stations. 18% of them (182) have built up by the end of June, and July adds the most, 363. Precipitation totals 28.8 inches a year, most in January (3.1") and least in August (1.4"); May to September bring 37% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 23 | 4 | 3.1 | 100% | 31 | 0 |
| Feb | 28 | 5 | 2.8 | 100% | 28 | 0 |
| Mar | 38 | 14 | 2.2 | 100% | 30 | 0 |
| Apr | 47 | 23 | 2.3 | 100% | 28 | 1 |
| May | 58 | 32 | 3.1 | 100% | 16 | 34 |
| Jun | 68 | 39 | 3.0 | 85% | 3 | 147 |
| Jul | 79 | 45 | 1.6 | 18% | <1 | 363 |
| Aug | 78 | 43 | 1.4 | 20% | 1 | 335 |
| Sep | 68 | 37 | 1.6 | 93% | 7 | 128 |
| Oct | 51 | 28 | 2.1 | 100% | 23 | 10 |
| Nov | 34 | 18 | 2.5 | 100% | 29 | 0 |
| Dec | 23 | 6 | 3.1 | 100% | 31 | 0 |
Monthly normals 1991–2020 at Hebgen Dam, MT (6,489 ft), NOAA NCEI. "32°F night": chance of at least one in the month. GDD: growing degree days, base 50°F.
When it snows in West Yellowstone, Montana
The first measurable snow (0.1 inch or more) in West Yellowstone usually arrives around October 20, and the last of the season around April 20. Those are the middle dates across the winters of 1991–2020 at Hebgen Dam, MT, 12.2 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 56 days after the last snow.
Planting calendar for 59758
| When | What to do |
|---|---|
| April 6 – April 20 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| April 20 – May 4 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| May 18 – June 1 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| June 15 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by June 18 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by August 27 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| September 10 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 59758 is 12 miles from Hebgen Dam, MT, which stands at 6,489 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 59758 in zone 4b, the band where the coldest night of the year averaged -25 to -20°F (-31.7 to -28.9°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.