USDA Hardiness Zone 4a
Frost Dates for 58801 — Williston, North Dakota
NOAA 1991–2020 normals from Williston Sloulin International Airport, ND (1,902 ft), 4 miles southeast.
Updated
In Williston, the last spring frost (32°F) is around May 21 in half of years and has passed by June 3 in nine years out of ten. The first fall frost comes around September 21, as early as September 9 one year in ten, leaving a typical freeze-free season of 123 days (NOAA, Williston Sloulin International Airport, ND).
- Last spring frost
- May 21
- First fall frost
- September 21
- Growing season
- 123 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
- October 22
- Last snow
- April 28
- Winters with snow
- 100%
- Snow per year
- 48.2"
median, 1991–2020
median, 1991–2020
22 of 22 observed
NOAA normal
Frost risk by date in Williston
Half of springs at Williston Sloulin International Airport, ND see their last 32°F night by May 21; only one in ten is past it by May 8, and one in ten still has one after June 3. Planting tender crops after May 26 leaves a 30% risk of a frost on them, after May 29 20%, and after June 3 10%. The 13 days between the even-odds date and the one-in-ten date is narrower than at 21% of the 33 North Dakota stations behind this site's ZIP pages.
In fall the first 32°F night comes by September 21 in half of years, as early as September 9 one year in ten, and holds off past October 2 one year in ten. A hard freeze of 28°F follows 7 days later, around September 28; in spring the one-in-ten date for 28°F is May 25, 9 days before the 32°F one. The freeze-free season lasts 123 days in a typical year, shorter than at 91% of the 33 North Dakota stations; it reaches 140 days one year in ten and falls short of 103 one year in ten. On average 191 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 8 days longer, to about May 29, and return around September 12. Severe cold of 16°F or below comes every winter, usually between October 25 and April 6.
| Low | 90% | 80% | 70% | 60% | 50% | 40% | 30% | 20% | 10% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | May 18 | May 22 | May 25 | May 27 | May 29 | Jun 1 | Jun 4 | Jun 8 | Jun 16 |
| 32°F | May 8 | May 13 | May 16 | May 18 | May 21 | May 24 | May 26 | May 29 | Jun 3 |
| 28°F | Apr 29 | May 3 | May 5 | May 8 | May 11 | May 14 | May 16 | May 20 | May 25 |
| 24°F | Apr 13 | Apr 19 | Apr 23 | Apr 27 | Apr 30 | May 3 | May 6 | May 10 | May 15 |
| 20°F | Apr 3 | Apr 7 | Apr 10 | Apr 14 | Apr 17 | Apr 20 | Apr 24 | Apr 29 | May 3 |
| 16°F | Mar 22 | Mar 30 | Apr 2 | Apr 4 | Apr 6 | Apr 10 | Apr 13 | Apr 17 | Apr 22 |
| Low | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Sep 1 | Sep 4 | Sep 7 | Sep 10 | Sep 12 | Sep 15 | Sep 17 | Sep 19 | Sep 23 |
| 32°F | Sep 9 | Sep 13 | Sep 17 | Sep 19 | Sep 21 | Sep 23 | Sep 25 | Sep 28 | Oct 2 |
| 28°F | Sep 16 | Sep 20 | Sep 23 | Sep 25 | Sep 28 | Sep 30 | Oct 3 | Oct 6 | Oct 11 |
| 24°F | Sep 23 | Sep 27 | Oct 1 | Oct 4 | Oct 7 | Oct 10 | Oct 13 | Oct 17 | Oct 21 |
| 20°F | Oct 1 | Oct 6 | Oct 10 | Oct 13 | Oct 16 | Oct 19 | Oct 22 | Oct 25 | Oct 30 |
| 16°F | Oct 9 | Oct 14 | Oct 19 | Oct 22 | Oct 25 | Oct 28 | Oct 31 | Nov 4 | Nov 9 |
Freeze probabilities 1991–2020 at Williston Sloulin International Airport, ND, 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 58801 →Compare Williston with another place →
Weather by month in Williston
July is the warmest month at Williston Sloulin International Airport, ND, averaging 85°F by day and 56°F at night; January is the coldest at 22°F and 1°F. A freezing night is all but certain in every month from October 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 15% of years.
Warmth for growing adds up to 2,149 growing degree days a year (base 50°F), fewer than at 55% of the 33 North Dakota stations. 29% of them (615) have built up by the end of June, and July adds the most, 632. Precipitation totals 15.2 inches a year, most in June (2.6") and least in February (0.5"); May to September bring 67% of it.
| Month | High °F | Low °F | Precip. in | 32°F night | Nights ≤ 32°F | GDD 50°F |
|---|---|---|---|---|---|---|
| Jan | 22 | 1 | 0.6 | 100% | 31 | 0 |
| Feb | 27 | 6 | 0.5 | 100% | 28 | 0 |
| Mar | 40 | 18 | 0.6 | 100% | 29 | 3 |
| Apr | 56 | 29 | 1.1 | 100% | 19 | 32 |
| May | 67 | 40 | 2.1 | 99% | 6 | 174 |
| Jun | 77 | 50 | 2.6 | 15% | <1 | 406 |
| Jul | 85 | 56 | 2.5 | 0% | 0 | 632 |
| Aug | 84 | 54 | 1.6 | 0% | 0 | 588 |
| Sep | 73 | 44 | 1.4 | 86% | 3 | 268 |
| Oct | 56 | 30 | 0.9 | 100% | 17 | 44 |
| Nov | 38 | 17 | 0.7 | 100% | 28 | 1 |
| Dec | 26 | 6 | 0.6 | 100% | 31 | 0 |
Monthly normals 1991–2020 at Williston Sloulin International Airport, ND (1,902 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, Watford City, ND, 34 miles southeast of Williston and 268 feet higher, has a last frost 12 days earlier (May 9), a first frost 6 days later (September 27), a season 16 days longer.
When it snows in Williston, North Dakota
The first measurable snow (0.1 inch or more) in Williston usually arrives around October 22, and the last of the season around April 28. Those are the middle dates across the winters of 1991–2020 at Williston Sloulin International Airport, ND, 4.4 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 23 days after the last snow.
Planting calendar for 58801
| When | What to do |
|---|---|
| March 12 – March 26 | Start peppers and aubergines indoorsThey need eight to ten weeks under lights before they can go out. |
| March 26 – April 9 | Start tomatoes indoorsSix to eight weeks gives a transplant big enough to set fruit early. |
| April 23 – May 7 | Sow peas, spinach, lettuce, radish outdoorsThese tolerate light frost and prefer to germinate in cool soil. |
| May 21 onward | Transplant tomatoes, peppers, basil, squash, cucumbersThe average last freeze has passed — still watch the actual forecast. |
| by June 29 | Sow the autumn crop of carrots, beets and brassicasThey need about twelve weeks to size up before growth stops. |
| by September 7 | Harvest tender crops, or be ready to cover themA first freeze two weeks early is well within normal variation. |
| September 21 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 58801 is 4 miles from Williston Sloulin International Airport, ND, which stands at 1,902 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 58801 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.
Frost dates across North Dakota →
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.