USDA Hardiness Zone 5a
Frost Dates for 59729 — Ennis, Montana
NOAA 1991–2020 normals from Ennis, MT (4,953 ft), 2 miles north.
Updated
In Ennis, the last spring frost (32°F) is around June 16 in half of years and has passed by July 6 in nine years out of ten. The first fall frost comes around September 4, as early as August 20 one year in ten, leaving a typical freeze-free season of 78 days (NOAA, Ennis, MT).
- Last spring frost
- June 16
- First fall frost
- September 4
- Growing season
- 78 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
- October 19
- Last snow
- April 29
- Winters with snow
- 97%
- Snow per year
- 44.7"
median, 1991–2020
median, 1991–2020
28 of 29 observed
NOAA normal
Frost risk by date in Ennis
Half of springs at Ennis, MT see their last 32°F night by June 16; only one in ten is past it by May 30, and one in ten still has one after July 6. Planting tender crops after June 23 leaves a 30% risk of a frost on them, after June 29 20%, and after July 6 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 4 in half of years, as early as August 20 one year in ten, and holds off past September 19 one year in ten. A hard freeze of 28°F follows 14 days later, around September 18; in spring the one-in-ten date for 28°F is June 12, 24 days before the 32°F one. The freeze-free season lasts 78 days in a typical year, the shortest of the 68 Montana stations; it reaches 103 days one year in ten and falls short of 53 one year in ten. On average 186 nights a year drop to 32°F or below. Severe cold of 16°F or below comes every winter, usually between October 25 and April 11.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | too rare for a date | ||||||||
| 32°F | May 30 | Jun 4 | Jun 8 | Jun 12 | Jun 16 | Jun 20 | Jun 23 | Jun 29 | Jul 6 |
| 28°F | May 9 | May 13 | May 17 | May 20 | May 23 | May 26 | May 30 | Jun 4 | Jun 12 |
| 24°F | Apr 24 | Apr 30 | May 3 | May 6 | May 8 | May 11 | May 13 | May 17 | May 22 |
| 20°F | Apr 10 | Apr 16 | Apr 19 | Apr 24 | Apr 28 | May 1 | May 4 | May 8 | May 12 |
| 16°F | Mar 25 | Apr 1 | Apr 5 | Apr 8 | Apr 11 | Apr 16 | Apr 20 | Apr 25 | May 2 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | too rare for a date | ||||||||
| 32°F | Aug 20 | Aug 25 | Aug 30 | Sep 1 | Sep 4 | Sep 6 | Sep 8 | Sep 13 | Sep 19 |
| 28°F | Sep 1 | Sep 6 | Sep 11 | Sep 14 | Sep 18 | Sep 21 | Sep 24 | Sep 28 | Oct 2 |
| 24°F | Sep 15 | Sep 22 | Sep 25 | Sep 28 | Oct 1 | Oct 3 | Oct 6 | Oct 11 | Oct 16 |
| 20°F | Sep 28 | Oct 2 | Oct 5 | Oct 9 | Oct 12 | Oct 16 | Oct 20 | Oct 24 | Oct 29 |
| 16°F | Oct 5 | Oct 14 | Oct 18 | Oct 21 | Oct 25 | Oct 28 | Oct 31 | Nov 3 | Nov 8 |
Freeze probabilities 1991–2020 at Ennis, 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 59729 →Compare Ennis with another place →
Weather by month in Ennis
July is the warmest month at Ennis, MT, averaging 83°F by day and 46°F at night; December is the coldest at 33°F and 15°F. A freezing night is all but certain in every month from September to May (a 90% chance or more). No month is safe from a 32°F night: even the warmest has at least a 10% chance. In spring, June still brings one in 86% of years and July still brings one in 18% of years.
Warmth for growing adds up to 1,385 growing degree days a year (base 50°F), fewer than at 93% of the 68 Montana stations. 23% of them (323) have built up by the end of June, and July adds the most, 439. Precipitation totals 12.9 inches a year, most in June (2.2") and least in January (0.5"); May to September bring 57% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 34 | 15 | 0.5 | 100% | 28 | 0 |
| Feb | 37 | 15 | 0.5 | 100% | 25 | 0 |
| Mar | 46 | 22 | 0.8 | 100% | 25 | 2 |
| Apr | 55 | 28 | 1.5 | 100% | 20 | 15 |
| May | 64 | 35 | 1.9 | 100% | 9 | 88 |
| Jun | 73 | 41 | 2.2 | 86% | 1 | 218 |
| Jul | 83 | 46 | 1.2 | 18% | <1 | 439 |
| Aug | 82 | 44 | 1.0 | 35% | 1 | 401 |
| Sep | 72 | 37 | 1.0 | 98% | 7 | 180 |
| Oct | 58 | 29 | 1.1 | 100% | 18 | 38 |
| Nov | 43 | 22 | 0.7 | 100% | 23 | 4 |
| Dec | 33 | 15 | 0.5 | 100% | 28 | 0 |
Monthly normals 1991–2020 at Ennis, MT (4,953 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, Hebgen Dam, MT, 35 miles southeast of Ennis and 1,536 feet higher, has a last frost 1 day earlier (June 15), a first frost 6 days later (September 10), a season 9 days longer.
When it snows in Ennis, Montana
The first measurable snow (0.1 inch or more) in Ennis usually arrives around October 19, and the last of the season around April 29. Those are the middle dates across the winters of 1991–2020 at Ennis, MT, 2.3 miles away: half of years saw snow earlier, half later. Snow fell in 97% of those winters. The last 32°F night of spring typically comes 48 days after the last snow.
Planting calendar for 59729
| When | What to do |
|---|---|
| April 7 – April 21 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| April 21 – May 5 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| May 19 – June 2 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| June 16 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by June 12 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by August 21 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| September 4 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 59729 is 2 miles from Ennis, MT, which stands at 4,953 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 59729 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.