U.S. Frost Dates by Weather Station

NOAA station USC00327027 · North Dakota

Frost Dates for Petersburg, ND

NOAA weather station Petersburg 2 N (USC00327027), North Dakota · elevation 1532 ft (467 m) · hardiness zone 4a*

  • Lower-risk planting dateafter May 25only 1 spring in 10 still has a frost later
  • Typical last frostMay 1150% chance of a frost after it
  • Typical first fall frostSeptember 2850% chance of a frost before it
  • Frost-free season138 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season at Petersburg, NDSpring: a frost after April 29 in 9 years out of 10, after May 11 in half of the years, after May 25 in 1 year out of 10. Fall: the first frost comes before September 16 in 1 year out of 10, before September 28 in half of the years, before October 10 in 9 years out of 10. Typical frost-free season: 138 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 11First frost ~Sep 28Frost season at Petersburg, NDSpring: a frost after April 29 in 9 years out of 10, after May 11 in half of the years, after May 25 in 1 year out of 10. Fall: the first frost comes before September 16 in 1 year out of 10, before September 28 in half of the years, before October 10 in 9 years out of 10. Typical frost-free season: 138 days.JFMAMJJASONDLast frost ~May 11First frost ~Sep 28
frost likely chance fading 90% → 10% frost-free in a typical yearThe year at a glance. Blue: frost is likely; the gradient fades as the chance drops from 90% to 10%; green: the frost-free part of a typical year.Today

Frost dates (32°F)

Probability of frost, based on 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 25September 16
50% (typical)May 11September 28
90% (likely)April 29October 10
Frost-free season (32°F, 50% chance)
138 days
Hard frost (28°F), last in spring, 50% chance after
May 2
Hard frost (28°F), first in fall, 50% chance before
October 7

The last 15 years (2006–2020 normals)

Typical last frost May 11 (same as the 30-year normal), typical first fall frost September 29 (1 day later). Frost-free season 140 days.

A shorter, more recent NOAA period. The 30-year normals above remain the main reference: 15 years carry more year-to-year noise.

Add these dates to your calendar Yearly reminders for the typical last frost, the lower-risk planting date and the typical first fall frost (.ics).

How the chance of frost changes with the date

Spring at Petersburg: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 25, 20% May 20, 30% May 17, 40% May 14, 50% May 11, 60% May 8, 70% May 5, 80% May 3, 90% April 29. Observed last spring frost in recent years: 2022 May 21, 2023 May 2, 2024 April 30, 2025 April 30, 2026 May 11.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 25May 11Apr 292022: May 212023: May 22024: April 302025: April 302026: May 11Fall at Petersburg: chance of a frost before this dateFall, chance of a frost before the date: 10% September 16, 20% September 21, 30% September 23, 40% September 26, 50% September 28, 60% September 30, 70% October 3, 80% October 6, 90% October 10. Observed first fall frost in recent years: 2021 October 16, 2022 October 6, 2023 October 7, 2024 October 15, 2025 October 7.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 16Sep 28Oct 102021: October 162022: October 62023: October 72024: October 152025: October 7
Two charts, because spring and fall answer different questions: in spring, the chance that a frost still comes after a date; in fall, the chance that the first frost has already come before it. NOAA publishes these odds from 10% to 90%, so the lines stop there. ◆ marks the actual date in each recent year.

What actually happened in recent years

Observed dates of the last spring and first fall frost (32°F) at this station; ◆ marks them on the charts above
YearLast spring frostFirst fall frost
2021incomplete recordOctober 16
2022May 21October 6
2023May 2October 7
2024April 30October 15
2025April 30October 7
2026May 11season not over yet

What these dates mean

Planting tender crops on April 29 in Petersburg is a gamble, because there is a 90 % chance of a light frost occurring after that date. The 50 % spring date, May 11, marks the point at which a light frost has a 50 % chance of occurring later, while the 50 % fall date, September 28, indicates a 50 % chance of a light frost occurring earlier. For a cautious plan, gardeners would wait until May 25 to set out tender crops, when only a 10 % chance of a later frost remains, and would aim to finish harvesting tender crops by September 16, when there is only a 10 % chance that a frost has arrived earlier. Hard frost at 28 °F can damage plants that would otherwise survive a light frost at 32 °F.

How to read the probabilities

The dates are probabilities from 30 years of weather, not a forecast for this year.

  • Spring: "10% after May 25" means that in about one spring out of ten a frost still happens after that date. The 90% date is the earliest: a frost after it happens in most years.
  • Fall: "10% before September 16" means that in about one fall out of ten the first frost arrives before that date.
  • 50% is the typical date: half of the years are earlier, half are later.
  • A light frost (32°F) damages tender plants; a hard frost (28°F) also stops most hardy vegetables.

Nearby weather stations

Map of weather stations near Petersburg, NDNumbered nearest stations: 1 — Grand Forks (Airport), ND — 39 mi; 2 — near Grand Forks, ND — 43 mi; 3 — McHenry, ND — 43 mi; 4 — Argyle, MN — 58 mi; 5 — Cavalier, ND — 59 mi.NDMN25 mi · 40 km1. Grand Forks (Airport), ND — 39 mi12. near Grand Forks, ND — 43 mi23. McHenry, ND — 43 mi34. Argyle, MN — 58 mi45. Cavalier, ND — 59 mi5
  1. Grand Forks (Airport), ND 39 mi (62 km)
  2. near Grand Forks, ND 43 mi (69 km)
  3. McHenry, ND 43 mi (69 km)
  4. Argyle, MN 58 mi (94 km)
  5. Cavalier, ND 59 mi (95 km)

Sources

* Hardiness zone 4a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 48.0356, -98.0097.