USDA Hardiness Zone 6a
Frost Dates for 59874 — Trout Creek, Montana
NOAA 1991–2020 normals from Trout Creek Rs, MT (2,356 ft), 2 miles northwest.
Updated
In Trout Creek, the last spring frost (32°F) is around May 20 in half of years and has passed by June 9 in nine years out of ten. The first fall frost comes around September 21, as early as September 2 one year in ten, leaving a typical freeze-free season of 122 days (NOAA, Trout Creek Rs, MT).
- Last spring frost
- May 20
- First fall frost
- September 21
- Growing season
- 122 days
- Hardiness zone
- 6a
50% probability
50% probability
freeze-free, 50%
-10 to -5°F (-23.3 to -20.6°C) coldest night
- First snow
- November 30
- Last snow
- March 4
- Winters with snow
- 96%
- Snow per year
- 51.4"
median, 1991–2020
median, 1991–2020
22 of 23 observed
NOAA normal
Frost risk by date in Trout Creek
Half of springs at Trout Creek Rs, MT see their last 32°F night by May 20; only one in ten is past it by May 5, and one in ten still has one after June 9. Planting tender crops after May 28 leaves a 30% risk of a frost on them, after June 1 20%, and after June 9 10%. The 20 days between the even-odds date and the one-in-ten date is wider than at 84% of the 68 Montana stations behind this site's ZIP pages.
In fall the first 32°F night comes by September 21 in half of years, as early as September 2 one year in ten, and holds off past October 9 one year in ten. A hard freeze of 28°F follows 17 days later, around October 8; in spring the one-in-ten date for 28°F is May 17, 23 days before the 32°F one. The freeze-free season lasts 122 days in a typical year, shorter than at 57% of the 68 Montana stations; it reaches 146 days one year in ten and falls short of 92 one year in ten. On average 165 nights a year drop to 32°F or below. Severe cold of 16°F or below comes every winter, usually between November 25 and March 3.
| 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 20 | May 24 | May 28 | Jun 1 | Jun 9 |
| 28°F | Apr 15 | Apr 21 | Apr 26 | Apr 30 | May 1 | May 4 | May 7 | May 11 | May 17 |
| 24°F | Mar 17 | Mar 25 | Mar 31 | Apr 4 | Apr 10 | Apr 15 | Apr 21 | Apr 27 | May 1 |
| 20°F | Feb 28 | Mar 5 | Mar 8 | Mar 13 | Mar 17 | Mar 21 | Mar 28 | Apr 2 | Apr 12 |
| 16°F | Feb 15 | Feb 22 | Feb 27 | Mar 1 | Mar 3 | Mar 6 | Mar 10 | Mar 14 | Mar 20 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | too rare for a date | ||||||||
| 32°F | Sep 2 | Sep 7 | Sep 12 | Sep 17 | Sep 21 | Sep 25 | Sep 28 | Oct 2 | Oct 9 |
| 28°F | Sep 21 | Sep 27 | Oct 1 | Oct 4 | Oct 8 | Oct 13 | Oct 18 | Oct 23 | Nov 1 |
| 24°F | Oct 3 | Oct 11 | Oct 18 | Oct 23 | Oct 28 | Nov 1 | Nov 5 | Nov 11 | Nov 19 |
| 20°F | Oct 18 | Oct 27 | Nov 1 | Nov 5 | Nov 10 | Nov 16 | Nov 21 | Nov 25 | Dec 1 |
| 16°F | Oct 29 | Nov 6 | Nov 13 | Nov 20 | Nov 25 | Nov 29 | Dec 3 | Dec 8 | Dec 16 |
Freeze probabilities 1991–2020 at Trout Creek Rs, 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 59874 →Compare Trout Creek with another place →
Weather by month in Trout Creek
July is the warmest month at Trout Creek Rs, MT, averaging 85°F by day and 49°F at night; December is the coldest at 33°F and 22°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 20% of years.
Warmth for growing adds up to 1,759 growing degree days a year (base 50°F), fewer than at 65% of the 68 Montana stations. 27% of them (473) have built up by the end of June, and July adds the most, 521. Precipitation totals 26.9 inches a year, most in December (3.7") and least in July (0.9"); May to September bring 28% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 34 | 22 | 3.2 | 100% | 29 | 0 |
| Feb | 39 | 23 | 2.3 | 100% | 25 | 0 |
| Mar | 48 | 28 | 1.9 | 100% | 24 | 2 |
| Apr | 58 | 32 | 1.8 | 100% | 16 | 27 |
| May | 68 | 39 | 2.1 | 94% | 6 | 154 |
| Jun | 74 | 45 | 2.4 | 20% | 1 | 291 |
| Jul | 85 | 49 | 0.9 | 3% | <1 | 521 |
| Aug | 85 | 47 | 0.9 | 6% | 0 | 486 |
| Sep | 74 | 41 | 1.3 | 72% | 3 | 240 |
| Oct | 58 | 35 | 2.9 | 99% | 12 | 39 |
| Nov | 41 | 29 | 3.5 | 100% | 21 | 1 |
| Dec | 33 | 22 | 3.7 | 100% | 29 | 0 |
Monthly normals 1991–2020 at Trout Creek Rs, MT (2,356 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, Thompson Falls Ph, MT, 21 miles southeast of Trout Creek, has a last frost 13 days earlier (May 7), a first frost 13 days later (October 4), a season 28 days longer.
When it snows in Trout Creek, Montana
The first measurable snow (0.1 inch or more) in Trout Creek usually arrives around November 30, and the last of the season around March 4. Those are the middle dates across the winters of 1991–2020 at Trout Creek Rs, MT, 1.9 miles away: half of years saw snow earlier, half later. Snow fell in 96% of those winters. The last 32°F night of spring typically comes 77 days after the last snow.
Planting calendar for 59874
| When | What to do |
|---|---|
| March 11 – March 25 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 25 – April 8 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 22 – May 6 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 20 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by June 29 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 7 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| September 21 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 59874 is 2 miles from Trout Creek Rs, MT, which stands at 2,356 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 59874 in zone 6a, the band where the coldest night of the year averaged -10 to -5°F (-23.3 to -20.6°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.