Frost Dates for 58501 — Bismarck, North Dakota

Half of springs at Bismarck 2.4 NNW, ND see their last 32°F night by May 10; only one in ten is past it by April 30, and one in ten still has one after May 23. Planting tender crops after May 14 leaves a 30% risk of a frost on them, after May 18 20%, and after May 23 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 30 in half of years, as early as September 16 one year in ten, and holds off past October 13 one year in ten. A hard freeze of 28°F follows 9 days later, around October 9; in spring the one-in-ten date for 28°F is May 13, 10 days before the 32°F one. The freeze-free season lasts 142 days in a typical year, longer than at 70% of the 33 North Dakota stations; it reaches 159 days one year in ten and falls short of 124 one year in ten. On average 181 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 10 days longer, to about May 20, and return around September 21. Severe cold of 16°F or below comes every winter, usually between November 4 and April 6.

July is the warmest month at Bismarck 2.4 NNW, ND, averaging 82°F by day and 58°F at night; January is the coldest at 22°F and 4°F. A freezing night is all but certain in every month from October to April (a 90% chance or more). From June to August the chance of a 32°F night stays under 10% each month. In spring, May still brings one in 88% of years.

Warmth for growing adds up to 2,158 growing degree days a year (base 50°F), fewer than at 52% of the 33 North Dakota stations. 30% of them (648) have built up by the end of June, and July adds the most, 617. Precipitation totals 20.2 inches a year, most in June (3.3") and least in January (0.5"); May to September bring 68% of it.

The nearest other station, Bismarck WFO, ND, 5 miles south of Bismarck and 180 feet lower, has a last frost 4 days later (May 14), the same first-frost date, a season 4 days shorter.

The first measurable snow (0.1 inch or more) in Bismarck usually arrives around October 29, and the last of the season around April 23. Those are the middle dates across the winters of 1991–2020 at Bismarck, ND, 4.8 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 17 days after the last snow.

ZIP 58501 is 1 mile from Bismarck 2.4 NNW, ND, which stands at 1,831 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. 1 other ZIP code shares the station; its figures are presented in full for 58503 (Bismarck). The 2023 USDA Plant Hardiness Zone Map lists ZIP 58501 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.