USDA Hardiness Zone 5a
Frost Dates for 59752 — Three Forks, Montana
NOAA 1991–2020 normals from Trident, MT (4,036 ft), 4 miles northeast.
Updated
In Three Forks, the last spring frost (32°F) is around May 9 in half of years and has passed by May 24 in nine years out of ten. The first fall frost comes around September 27, as early as September 12 one year in ten, leaving a typical freeze-free season of 139 days (NOAA, Trident, MT).
- Last spring frost
- May 9
- First fall frost
- September 27
- Growing season
- 139 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 10
- Last snow
- April 17
- Winters with snow
- 100%
- Snow per year
- —
median, 1991–2020
median, 1991–2020
19 of 19 observed
NOAA normal
Frost risk by date in Three Forks
Half of springs at Trident, MT see their last 32°F night by May 9; only one in ten is past it by April 29, and one in ten still has one after May 24. Planting tender crops after May 14 leaves a 30% risk of a frost on them, after May 18 20%, and after May 24 10%. The 15 days between the even-odds date and the one-in-ten date is narrower than at 53% of the 68 Montana stations behind this site's ZIP pages.
In fall the first 32°F night comes by September 27 in half of years, as early as September 12 one year in ten, and holds off past October 9 one year in ten. A hard freeze of 28°F follows 9 days later, around October 6; in spring the one-in-ten date for 28°F is May 10, 14 days before the 32°F one. The freeze-free season lasts 139 days in a typical year, longer than at 75% of the 68 Montana stations; it reaches 156 days one year in ten and falls short of 120 one year in ten. On average 174 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 15 days longer, to about May 24, and return around September 15. Severe cold of 16°F or below comes every winter, usually between November 5 and March 18.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 10 | May 14 | May 17 | May 21 | May 24 | May 28 | May 31 | Jun 3 | Jun 10 |
| 32°F | Apr 29 | May 2 | May 4 | May 6 | May 9 | May 11 | May 14 | May 18 | May 24 |
| 28°F | Apr 12 | Apr 19 | Apr 23 | Apr 26 | Apr 29 | May 1 | May 3 | May 6 | May 10 |
| 24°F | Mar 29 | Apr 3 | Apr 8 | Apr 12 | Apr 15 | Apr 18 | Apr 22 | Apr 27 | Apr 30 |
| 20°F | Mar 10 | Mar 17 | Mar 24 | Mar 29 | Apr 1 | Apr 4 | Apr 8 | Apr 13 | Apr 17 |
| 16°F | Feb 28 | Mar 4 | Mar 10 | Mar 14 | Mar 18 | Mar 23 | Mar 28 | Apr 2 | Apr 8 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 1 | Sep 6 | Sep 10 | Sep 12 | Sep 15 | Sep 19 | Sep 22 | Sep 25 | Sep 30 |
| 32°F | Sep 12 | Sep 18 | Sep 22 | Sep 24 | Sep 27 | Sep 29 | Oct 2 | Oct 5 | Oct 9 |
| 28°F | Sep 24 | Sep 28 | Oct 1 | Oct 4 | Oct 6 | Oct 10 | Oct 13 | Oct 17 | Oct 22 |
| 24°F | Oct 1 | Oct 4 | Oct 9 | Oct 13 | Oct 17 | Oct 20 | Oct 24 | Oct 28 | Nov 1 |
| 20°F | Oct 9 | Oct 16 | Oct 20 | Oct 25 | Oct 29 | Nov 1 | Nov 2 | Nov 6 | Nov 11 |
| 16°F | Oct 18 | Oct 24 | Oct 30 | Nov 1 | Nov 5 | Nov 8 | Nov 11 | Nov 15 | Nov 20 |
Freeze probabilities 1991–2020 at Trident, 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 59752 →Compare Three Forks with another place →
Weather by month in Three Forks
July is the warmest month at Trident, MT, averaging 85°F by day and 54°F at night; December is the coldest at 33°F and 15°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 84% of years.
Warmth for growing adds up to 1,997 growing degree days a year (base 50°F), more than at 62% of the 68 Montana stations. 27% of them (534) have built up by the end of June, and July adds the most, 595. Precipitation totals 13.2 inches a year, most in June (2.4") and least in February (0.3"); May to September bring 61% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 33 | 16 | 0.4 | 100% | 30 | 0 |
| Feb | 37 | 18 | 0.3 | 100% | 26 | 1 |
| Mar | 48 | 26 | 0.7 | 100% | 25 | 5 |
| Apr | 56 | 33 | 1.5 | 100% | 17 | 29 |
| May | 66 | 42 | 2.2 | 84% | 4 | 161 |
| Jun | 74 | 49 | 2.4 | 2% | <1 | 339 |
| Jul | 85 | 54 | 1.4 | 0% | 0 | 595 |
| Aug | 84 | 51 | 1.0 | 2% | <1 | 539 |
| Sep | 73 | 43 | 1.1 | 63% | 3 | 268 |
| Oct | 58 | 33 | 0.9 | 100% | 16 | 57 |
| Nov | 42 | 23 | 0.6 | 100% | 26 | 4 |
| Dec | 33 | 15 | 0.7 | 100% | 29 | 0 |
Monthly normals 1991–2020 at Trident, MT (4,036 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, Logan Landfill, MT, 6 miles east of Three Forks and 207 feet higher, has a last frost 17 days later (May 26), a first frost 12 days earlier (September 15), a season 28 days shorter.
When it snows in Three Forks, Montana
The first measurable snow (0.1 inch or more) in Three Forks usually arrives around November 10, and the last of the season around April 17. Those are the middle dates across the winters of 1991–2020 at Trident, MT, 4.2 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 22 days after the last snow.
Planting calendar for 59752
| 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 5 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 13 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| September 27 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 59752 is 4 miles from Trident, MT, which stands at 4,036 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 59752 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.