USDA Hardiness Zone 5a
Frost Dates for 59741 — Manhattan, Montana
NOAA 1991–2020 normals from Logan Landfill, MT (4,243 ft), 6 miles northwest.
Updated
In Manhattan, the last spring frost (32°F) is around May 26 in half of years and has passed by June 12 in nine years out of ten. The first fall frost comes around September 15, as early as September 1 one year in ten, leaving a typical freeze-free season of 111 days (NOAA, Logan Landfill, MT).
- Last spring frost
- May 26
- First fall frost
- September 15
- Growing season
- 111 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 Manhattan
Half of springs at Logan Landfill, MT see their last 32°F night by May 26; only one in ten is past it by May 11, and one in ten still has one after June 12. Planting tender crops after June 1 leaves a 30% risk of a frost on them, after June 4 20%, and after June 12 10%. The 17 days between the even-odds date and the one-in-ten date is wider than at 62% of the 68 Montana stations behind this site's ZIP pages.
In fall the first 32°F night comes by September 15 in half of years, as early as September 1 one year in ten, and holds off past September 28 one year in ten. A hard freeze of 28°F follows 12 days later, around September 27; in spring the one-in-ten date for 28°F is May 27, 16 days before the 32°F one. The freeze-free season lasts 111 days in a typical year, shorter than at 78% of the 68 Montana stations; it reaches 132 days one year in ten and falls short of 90 one year in ten. On average 200 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 17 days longer, to about June 12, and return around September 3. Severe cold of 16°F or below comes every winter, usually between October 26 and April 4.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 29 | Jun 2 | Jun 5 | Jun 9 | Jun 12 | Jun 16 | Jun 19 | Jun 24 | Jul 3 |
| 32°F | May 11 | May 16 | May 19 | May 23 | May 26 | May 29 | Jun 1 | Jun 4 | Jun 12 |
| 28°F | Apr 29 | May 3 | May 5 | May 8 | May 11 | May 13 | May 17 | May 21 | May 27 |
| 24°F | Apr 14 | Apr 20 | Apr 24 | Apr 28 | Apr 30 | May 2 | May 5 | May 9 | May 15 |
| 20°F | Apr 2 | Apr 6 | Apr 10 | Apr 13 | Apr 17 | Apr 21 | Apr 24 | Apr 29 | May 3 |
| 16°F | Mar 15 | Mar 23 | Mar 29 | Apr 1 | Apr 4 | Apr 7 | Apr 12 | Apr 17 | Apr 24 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Aug 17 | Aug 24 | Aug 29 | Sep 1 | Sep 3 | Sep 6 | Sep 9 | Sep 12 | Sep 16 |
| 32°F | Sep 1 | Sep 6 | Sep 9 | Sep 12 | Sep 15 | Sep 17 | Sep 21 | Sep 24 | Sep 28 |
| 28°F | Sep 12 | Sep 18 | Sep 22 | Sep 25 | Sep 27 | Sep 29 | Oct 1 | Oct 4 | Oct 8 |
| 24°F | Sep 23 | Sep 28 | Oct 1 | Oct 3 | Oct 5 | Oct 8 | Oct 11 | Oct 14 | Oct 18 |
| 20°F | Oct 1 | Oct 5 | Oct 9 | Oct 13 | Oct 16 | Oct 20 | Oct 23 | Oct 26 | Oct 30 |
| 16°F | Oct 9 | Oct 15 | Oct 20 | Oct 23 | Oct 26 | Oct 29 | Nov 1 | Nov 4 | Nov 9 |
Freeze probabilities 1991–2020 at Logan Landfill, 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 59741 →Compare Manhattan with another place →
Weather by month in Manhattan
July is the warmest month at Logan Landfill, MT, averaging 85°F by day and 49°F at night; January is the coldest at 33°F and 10°F. A freezing night is all but certain in every month from September 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 30% of years.
Warmth for growing adds up to 1,612 growing degree days a year (base 50°F), fewer than at 79% of the 68 Montana stations. 24% of them (382) have built up by the end of June, and July adds the most, 521.
| Month | High °F | Low °F | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|
| Jan | 33 | 10 | 100% | 30 | 0 |
| Feb | 37 | 13 | 100% | 27 | 1 |
| Mar | 46 | 21 | 100% | 28 | 1 |
| Apr | 55 | 29 | 100% | 22 | 15 |
| May | 64 | 36 | 99% | 8 | 98 |
| Jun | 73 | 44 | 30% | 1 | 266 |
| Jul | 85 | 49 | 1% | <1 | 521 |
| Aug | 83 | 46 | 10% | <1 | 458 |
| Sep | 73 | 39 | 92% | 5 | 211 |
| Oct | 58 | 28 | 100% | 22 | 38 |
| Nov | 42 | 19 | 100% | 27 | 1 |
| Dec | 32 | 11 | 100% | 30 | 0 |
Monthly normals 1991–2020 at Logan Landfill, MT (4,243 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, Bozeman Gallatin Field, MT, 8 miles east of Manhattan and 184 feet higher, has the same 50% last-frost date, a first frost 1 day later (September 16), a season 1 day longer.
When it snows in Manhattan, Montana
The first measurable snow (0.1 inch or more) in Manhattan 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, 11.7 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 39 days after the last snow.
Planting calendar for 59741
| When | What to do |
|---|---|
| March 17 – March 31 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 31 – April 14 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 28 – May 12 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 26 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by June 23 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 1 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| September 15 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 59741 is 6 miles from Logan Landfill, MT, which stands at 4,243 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 59741 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.