USDA Hardiness Zone 5b
Frost Dates for 59901 — Kalispell, Montana
NOAA 1991–2020 normals from Kalispell Glacier Airport, MT (2,957 ft), 8 miles north.
Updated
In Kalispell, the last spring frost (32°F) is around May 31 in half of years and has passed by June 22 in nine years out of ten. The first fall frost comes around September 10, as early as August 26 one year in ten, leaving a typical freeze-free season of 100 days (NOAA, Kalispell Glacier Airport, MT).
- Last spring frost
- May 31
- First fall frost
- September 10
- Growing season
- 100 days
- Hardiness zone
- 5b
50% probability
50% probability
freeze-free, 50%
-15 to -10°F (-26.1 to -23.3°C) coldest night
- First snow
- November 3
- Last snow
- April 13
- Winters with snow
- 100%
- Snow per year
- 54.4"
median, 1991–2020
median, 1991–2020
25 of 25 observed
NOAA normal
Frost risk by date in Kalispell
Half of springs at Kalispell Glacier Airport, MT see their last 32°F night by May 31; only one in ten is past it by May 13, and one in ten still has one after June 22. Planting tender crops after June 7 leaves a 30% risk of a frost on them, after June 14 20%, and after June 22 10%. The 22 days between the even-odds date and the one-in-ten date is wider than at 93% of the 68 Montana stations behind this site's ZIP pages, so a fixed calendar date is a gamble here.
In fall the first 32°F night comes by September 10 in half of years, as early as August 26 one year in ten, and holds off past September 25 one year in ten. A hard freeze of 28°F follows 17 days later, around September 27; in spring the one-in-ten date for 28°F is May 26, 27 days before the 32°F one. The freeze-free season lasts 100 days in a typical year, shorter than at 88% of the 68 Montana stations; it reaches 123 days one year in ten and falls short of 70 one year in ten. On average 187 nights a year drop to 32°F or below. Severe cold of 16°F or below comes every winter, usually between November 1 and March 15.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | too rare for a date | ||||||||
| 32°F | May 13 | May 19 | May 23 | May 27 | May 31 | Jun 3 | Jun 7 | Jun 14 | Jun 22 |
| 28°F | Apr 28 | May 2 | May 5 | May 8 | May 10 | May 13 | May 16 | May 20 | May 26 |
| 24°F | Apr 9 | Apr 16 | Apr 21 | Apr 24 | Apr 28 | May 1 | May 4 | May 7 | May 11 |
| 20°F | Mar 14 | Mar 21 | Mar 27 | Mar 31 | Apr 3 | Apr 8 | Apr 14 | Apr 18 | Apr 25 |
| 16°F | Feb 28 | Mar 5 | Mar 8 | Mar 12 | Mar 15 | Mar 19 | Mar 25 | Mar 30 | Apr 5 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | too rare for a date | ||||||||
| 32°F | Aug 26 | Aug 31 | Sep 4 | Sep 7 | Sep 10 | Sep 13 | Sep 17 | Sep 21 | Sep 25 |
| 28°F | Sep 9 | Sep 17 | Sep 20 | Sep 23 | Sep 27 | Sep 29 | Oct 1 | Oct 3 | Oct 7 |
| 24°F | Sep 24 | Sep 29 | Oct 1 | Oct 4 | Oct 6 | Oct 9 | Oct 13 | Oct 16 | Oct 21 |
| 20°F | Oct 3 | Oct 8 | Oct 12 | Oct 16 | Oct 19 | Oct 22 | Oct 25 | Oct 30 | Nov 4 |
| 16°F | Oct 14 | Oct 20 | Oct 25 | Oct 28 | Nov 1 | Nov 4 | Nov 9 | Nov 15 | Nov 25 |
Freeze probabilities 1991–2020 at Kalispell Glacier 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 59901 →Compare Kalispell with another place →
Frost risk through the year in Kalispell
In Kalispell, the spring curve drops under 10% on June 22 and the fall curve passes 10% on August 26, 65 days later; that gap is shorter than at 90% of the 68 Montana stations with frost dates. The spring risk falls from 90% to 10% over 40 days (May 13 to June 22) and the fall risk climbs from 10% to 90% over 30 days (August 26 to September 25): the last frost moves more from year to year than the first. At Whitefish, MT, 14 miles north, the same gap runs from June 6 to September 8, 29 days longer.
| Planted on | Another 32°F night | 28°F night |
|---|---|---|
| May 17 | 83% | 28% |
| May 24 | 68% | 13% |
| May 3150% date | 50% | under 10% |
| Jun 7 | 30% | under 10% |
| Jun 14 | 20% | under 10% |
| Jun 21 | 11% | under 10% |
Weather by month in Kalispell
July is the warmest month at Kalispell Glacier Airport, MT, averaging 82°F by day and 48°F at night; January is the coldest at 31°F and 16°F. A freezing night is all but certain in every month from September to May (a 90% chance or more). July is the only month with under a 10% chance of a 32°F night. In spring, June still brings one in 44% of years.
Warmth for growing adds up to 1,425 growing degree days a year (base 50°F), fewer than at 91% of the 68 Montana stations. 25% of them (358) have built up by the end of June, and July adds the most, 462. Precipitation totals 16.8 inches a year, most in June (2.8") and least in August (0.8"); May to September bring 46% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 31 | 16 | 1.4 | 100% | 29 | 0 |
| Feb | 36 | 18 | 1.0 | 100% | 27 | 0 |
| Mar | 45 | 24 | 1.1 | 100% | 27 | 0 |
| Apr | 55 | 31 | 1.3 | 100% | 18 | 13 |
| May | 65 | 38 | 1.8 | 97% | 6 | 109 |
| Jun | 71 | 44 | 2.8 | 44% | 1 | 236 |
| Jul | 82 | 48 | 1.1 | 6% | <1 | 462 |
| Aug | 82 | 46 | 0.8 | 20% | <1 | 426 |
| Sep | 70 | 38 | 1.2 | 95% | 5 | 164 |
| Oct | 54 | 29 | 1.4 | 100% | 20 | 16 |
| Nov | 39 | 24 | 1.4 | 100% | 25 | 0 |
| Dec | 31 | 17 | 1.5 | 100% | 30 | 0 |
Monthly normals 1991–2020 at Kalispell Glacier Airport, MT (2,957 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, Whitefish, MT, 14 miles north of Kalispell, has a last frost 15 days earlier (May 16), a first frost 15 days later (September 25), a season 29 days longer.
When it snows in Kalispell, Montana
The first measurable snow (0.1 inch or more) in Kalispell usually arrives around November 3, and the last of the season around April 13. Those are the middle dates across the winters of 1991–2020 at Kalispell Glacier Airport, MT, 7.6 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 48 days after the last snow.
Planting calendar for 59901
| When | What to do |
|---|---|
| March 22 – April 5 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| April 5 – April 19 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| May 3 – May 17 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 31 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by June 18 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by August 27 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| September 10 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 59901 is 8 miles from Kalispell Glacier Airport, MT, which stands at 2,957 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 59901 in zone 5b, the band where the coldest night of the year averaged -15 to -10°F (-26.1 to -23.3°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.