Frost Dates for 58401 — Jamestown, North Dakota

Half of springs at Jamestown State Hosp, ND see their last 32°F night by May 8; only one in ten is past it by April 26, and one in ten still has one after May 21. Planting tender crops after May 13 leaves a 30% risk of a frost on them, after May 16 20%, and after May 21 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 29 in half of years, as early as September 17 one year in ten, and holds off past October 11 one year in ten. A hard freeze of 28°F follows 8 days later, around October 7; in spring the one-in-ten date for 28°F is May 12, 9 days before the 32°F one. The freeze-free season lasts 143 days in a typical year, longer than at 73% of the 33 North Dakota stations; it reaches 161 days one year in ten and falls short of 127 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 9 days longer, to about May 17, and return around September 21. Severe cold of 16°F or below comes every winter, usually between November 6 and April 3.

July is the warmest month at Jamestown State Hosp, ND, averaging 82°F by day and 59°F at night; January is the coldest at 18°F and 0°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 78% of years.

Warmth for growing adds up to 2,209 growing degree days a year (base 50°F), more than at 58% of the 33 North Dakota stations. 31% of them (693) have built up by the end of June, and July adds the most, 621. Precipitation totals 21.0 inches a year, most in June (3.6") and least in January (0.5"); May to September bring 72% of it.

The nearest other station, Valley City 3 NNW, ND, 34 miles east of Jamestown and 257 feet lower, has a last frost 5 days later (May 13), a first frost 3 days earlier (September 26), a season 7 days shorter.

The first measurable snow (0.1 inch or more) in Jamestown usually arrives around November 4, and the last of the season around April 4. Those are the middle dates across the winters of 1991–2020 at Jamestown State Hosp, ND, 2.6 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 34 days after the last snow.

ZIP 58401 is 3 miles from Jamestown State Hosp, ND, which stands at 1,467 feet, the nearest NOAA station that publishes freeze probabilities for 1991–2020. The 2023 USDA Plant Hardiness Zone Map lists ZIP 58401 in zone 4b, the band where the coldest night of the year averaged -25 to -20°F (-31.7 to -28.9°C) over 1991–2020; a zone describes winter lows, not frost dates.