Frost Dates for 58045 — Hillsboro, North Dakota

Half of springs at Hillsboro 3 N, ND see their last 32°F night by May 2; only one in ten is past it by April 15, and one in ten still has one after May 17. Planting tender crops after May 8 leaves a 30% risk of a frost on them, after May 12 20%, and after May 17 10%. The 15 days between the even-odds date and the one-in-ten date is the widest of the 33 North Dakota stations behind this site's ZIP pages.

In fall the first 32°F night comes by October 9 in half of years, as early as September 25 one year in ten, and holds off past October 25 one year in ten. A hard freeze of 28°F follows 11 days later, around October 20; in spring the one-in-ten date for 28°F is May 8, 9 days before the 32°F one. The freeze-free season lasts 158 days in a typical year, the longest of the 33 North Dakota stations; it reaches 179 days one year in ten and falls short of 139 one year in ten. On average 174 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 9 days longer, to about May 11, and return around September 30. Severe cold of 16°F or below comes every winter, usually between November 12 and March 30.

July is the warmest month at Hillsboro 3 N, ND, averaging 81°F by day and 61°F at night; January is the coldest at 18°F and 1°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 57% of years.

Warmth for growing adds up to 2,465 growing degree days a year (base 50°F), more than at 97% of the 33 North Dakota stations. 33% of them (810) have built up by the end of June, and July adds the most, 657. Precipitation totals 22.5 inches a year, most in June (3.7") and least in January (0.6"); May to September bring 65% of it.

The nearest other station, Mayville, ND, 16 miles northwest of Hillsboro, has a last frost 11 days later (May 13), a first frost 12 days earlier (September 27), a season 22 days shorter.

The first measurable snow (0.1 inch or more) in Hillsboro usually arrives around November 5, and the last of the season around April 12. Those are the middle dates across the winters of 1991–2020 at Georgetown 1 E, MN, 25.1 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 20 days after the last snow.

ZIP 58045 is 4 miles from Hillsboro 3 N, ND, which stands at 910 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 58045 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.