USDA Hardiness Zone 4a
Frost Dates for 59526 — Harlem, Montana
NOAA 1991–2020 normals from Fort Belknap 2 SW, MT (2,527 ft), 3 miles southwest.
Updated
In Harlem, the last spring frost (32°F) is around May 16 in half of years and has passed by May 28 in nine years out of ten. The first fall frost comes around September 22, as early as September 10 one year in ten, leaving a typical freeze-free season of 128 days (NOAA, Fort Belknap 2 SW, MT).
- Last spring frost
- May 16
- First fall frost
- September 22
- Growing season
- 128 days
- Hardiness zone
- 4a
50% probability
50% probability
freeze-free, 50%
-30 to -25°F (-34.4 to -31.7°C) coldest night
- First snow
- November 18
- Last snow
- February 27
- Winters with snow
- 89%
- Snow per year
- —
median, 1991–2020
median, 1991–2020
16 of 18 observed
NOAA normal
Frost risk by date in Harlem
Half of springs at Fort Belknap 2 SW, MT see their last 32°F night by May 16; only one in ten is past it by May 6, and one in ten still has one after May 28. Planting tender crops after May 21 leaves a 30% risk of a frost on them, after May 24 20%, and after May 28 10%. The 12 days between the even-odds date and the one-in-ten date is the narrowest of the 68 Montana stations behind this site's ZIP pages.
In fall the first 32°F night comes by September 22 in half of years, as early as September 10 one year in ten, and holds off past October 3 one year in ten. A hard freeze of 28°F follows 8 days later, around September 30; in spring the one-in-ten date for 28°F is May 16, 12 days before the 32°F one. The freeze-free season lasts 128 days in a typical year, longer than at 51% of the 68 Montana stations; it reaches 144 days one year in ten and falls short of 110 one year in ten. On average 195 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 28, and return around September 12. Severe cold of 16°F or below comes every winter, usually between October 27 and April 5.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 17 | May 21 | May 24 | May 25 | May 28 | May 31 | Jun 2 | Jun 6 | Jun 12 |
| 32°F | May 6 | May 10 | May 12 | May 14 | May 16 | May 18 | May 21 | May 24 | May 28 |
| 28°F | Apr 24 | Apr 29 | May 1 | May 4 | May 6 | May 8 | May 10 | May 13 | May 16 |
| 24°F | Apr 10 | Apr 15 | Apr 20 | Apr 23 | Apr 26 | Apr 28 | May 1 | May 4 | May 7 |
| 20°F | Mar 31 | Apr 4 | Apr 7 | Apr 11 | Apr 14 | Apr 17 | Apr 21 | Apr 25 | Apr 29 |
| 16°F | Mar 17 | Mar 24 | Mar 30 | Apr 2 | Apr 5 | Apr 7 | Apr 11 | Apr 15 | Apr 20 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Aug 29 | Sep 3 | Sep 7 | Sep 10 | Sep 12 | Sep 14 | Sep 17 | Sep 20 | Sep 24 |
| 32°F | Sep 10 | Sep 15 | Sep 18 | Sep 20 | Sep 22 | Sep 24 | Sep 27 | Sep 30 | Oct 3 |
| 28°F | Sep 19 | Sep 22 | Sep 25 | Sep 28 | Sep 30 | Oct 2 | Oct 5 | Oct 8 | Oct 13 |
| 24°F | Sep 24 | Sep 30 | Oct 3 | Oct 6 | Oct 9 | Oct 12 | Oct 14 | Oct 17 | Oct 21 |
| 20°F | Oct 2 | Oct 7 | Oct 12 | Oct 15 | Oct 18 | Oct 20 | Oct 22 | Oct 26 | Oct 30 |
| 16°F | Oct 11 | Oct 16 | Oct 20 | Oct 24 | Oct 27 | Oct 30 | Nov 1 | Nov 5 | Nov 10 |
Freeze probabilities 1991–2020 at Fort Belknap 2 SW, 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 59526 →Compare Harlem with another place →
Compared with the next station
The nearest other station, Chinook, MT, 24 miles west of Harlem, has a last frost 2 days earlier (May 14), a first frost 1 day later (September 23), a season 2 days longer.
When it snows in Harlem, Montana
The first measurable snow (0.1 inch or more) in Harlem usually arrives around November 18, and the last of the season around February 27. Those are the middle dates across the winters of 1991–2020 at Harlem, MT, 5 miles away: half of years saw snow earlier, half later. Snow fell in 89% of those winters. The last 32°F night of spring typically comes 78 days after the last snow.
Planting calendar for 59526
| When | What to do |
|---|---|
| March 7 – March 21 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 21 – April 4 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 18 – May 2 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 16 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by June 30 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 8 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| September 22 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 59526 is 3 miles from Fort Belknap 2 SW, MT, which stands at 2,527 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 59526 in zone 4a, the band where the coldest night of the year averaged -30 to -25°F (-34.4 to -31.7°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.