USDA Hardiness Zone 3b
Frost Dates for 59501 — Havre, Montana
NOAA 1991–2020 normals from Havre City Co Airport, MT (2,585 ft), 3 miles south.
Updated
In Havre, the last spring frost (32°F) is around May 15 in half of years and has passed by May 27 in nine years out of ten. The first fall frost comes around September 23, as early as September 11 one year in ten, leaving a typical freeze-free season of 129 days (NOAA, Havre City Co Airport, MT).
- Last spring frost
- May 15
- First fall frost
- September 23
- Growing season
- 129 days
- Hardiness zone
- 3b
50% probability
50% probability
freeze-free, 50%
-35 to -30°F (-37.2 to -34.4°C) coldest night
- First snow
- October 27
- Last snow
- April 13
- Winters with snow
- 100%
- Snow per year
- 41"
median, 1991–2020
median, 1991–2020
25 of 25 observed
NOAA normal
Frost risk by date in Havre
Half of springs at Havre City Co Airport, MT see their last 32°F night by May 15; only one in ten is past it by May 3, and one in ten still has one after May 27. Planting tender crops after May 20 leaves a 30% risk of a frost on them, after May 24 20%, and after May 27 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 23 in half of years, as early as September 11 one year in ten, and holds off past October 5 one year in ten. A hard freeze of 28°F follows 8 days later, around October 1; in spring the one-in-ten date for 28°F is May 16, 11 days before the 32°F one. The freeze-free season lasts 129 days in a typical year, longer than at 54% of the 68 Montana stations; it reaches 146 days one year in ten and falls short of 112 one year in ten. On average 185 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 27, and return around September 12. Severe cold of 16°F or below comes every winter, usually between October 29 and April 2.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 16 | May 20 | May 23 | May 25 | May 27 | May 30 | Jun 2 | Jun 5 | Jun 11 |
| 32°F | May 3 | May 8 | May 11 | May 13 | May 15 | May 17 | May 20 | May 24 | May 27 |
| 28°F | Apr 20 | Apr 25 | Apr 29 | May 1 | May 3 | May 6 | May 8 | May 11 | May 16 |
| 24°F | Apr 7 | Apr 11 | Apr 16 | Apr 19 | Apr 22 | Apr 25 | Apr 28 | May 1 | May 4 |
| 20°F | Mar 24 | Mar 31 | Apr 4 | Apr 8 | Apr 12 | Apr 15 | Apr 19 | Apr 22 | Apr 29 |
| 16°F | Mar 12 | Mar 19 | Mar 25 | Mar 30 | Apr 2 | Apr 5 | Apr 8 | Apr 11 | Apr 18 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Aug 29 | Sep 3 | Sep 6 | Sep 10 | Sep 12 | Sep 16 | Sep 18 | Sep 20 | Sep 23 |
| 32°F | Sep 11 | Sep 16 | Sep 19 | Sep 21 | Sep 23 | Sep 26 | Sep 28 | Oct 1 | Oct 5 |
| 28°F | Sep 19 | Sep 23 | Sep 26 | Sep 29 | Oct 1 | Oct 3 | Oct 6 | Oct 9 | Oct 15 |
| 24°F | Sep 26 | Oct 1 | Oct 4 | Oct 7 | Oct 11 | Oct 14 | Oct 17 | Oct 20 | Oct 26 |
| 20°F | Oct 3 | Oct 9 | Oct 14 | Oct 17 | Oct 20 | Oct 24 | Oct 27 | Oct 30 | Nov 4 |
| 16°F | Oct 13 | Oct 18 | Oct 23 | Oct 26 | Oct 29 | Nov 1 | Nov 4 | Nov 7 | Nov 14 |
Freeze probabilities 1991–2020 at Havre City Co Airport, 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 59501 →Compare Havre with another place →
Weather by month in Havre
July is the warmest month at Havre City Co Airport, MT, averaging 86°F by day and 54°F at night; January is the coldest at 28°F and 7°F. A freezing night is all but certain in every month from October to May (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month.
Warmth for growing adds up to 2,077 growing degree days a year (base 50°F), more than at 66% of the 68 Montana stations. 28% of them (573) have built up by the end of June, and July adds the most, 615. Precipitation totals 11.9 inches a year, most in June (2.5") and least in January (0.4"); May to September bring 66% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 28 | 7 | 0.4 | 100% | 30 | 0 |
| Feb | 33 | 10 | 0.4 | 100% | 27 | 1 |
| Mar | 44 | 20 | 0.5 | 100% | 28 | 4 |
| Apr | 57 | 31 | 1.0 | 100% | 18 | 33 |
| May | 68 | 40 | 1.9 | 93% | 5 | 169 |
| Jun | 76 | 49 | 2.5 | 6% | <1 | 366 |
| Jul | 86 | 54 | 1.5 | 0% | 0 | 615 |
| Aug | 85 | 52 | 0.9 | 1% | 0 | 572 |
| Sep | 73 | 43 | 1.1 | 78% | 3 | 259 |
| Oct | 58 | 31 | 0.8 | 100% | 18 | 54 |
| Nov | 42 | 20 | 0.5 | 100% | 26 | 5 |
| Dec | 32 | 11 | 0.4 | 100% | 30 | 0 |
Monthly normals 1991–2020 at Havre City Co Airport, MT (2,585 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, Chinook, MT, 25 miles east of Havre and 165 feet lower, has a last frost 1 day earlier (May 14), the same first-frost date, a season 1 day longer.
When it snows in Havre, Montana
The first measurable snow (0.1 inch or more) in Havre usually arrives around October 27, and the last of the season around April 13. Those are the middle dates across the winters of 1991–2020 at Havre City Co Airport, MT, 3 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 32 days after the last snow.
Planting calendar for 59501
| When | What to do |
|---|---|
| March 6 – March 20 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 20 – April 3 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 17 – May 1 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 15 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by July 1 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 9 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| September 23 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 59501 is 3 miles from Havre City Co Airport, MT, which stands at 2,585 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 59501 in zone 3b, the band where the coldest night of the year averaged -35 to -30°F (-37.2 to -34.4°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.