U.S. Frost Dates by Weather Station

NOAA station USC00327311 · North Dakota

Frost Dates for Pretty Rock, ND

NOAA weather station Pretty Rock (USC00327311), North Dakota · elevation 2480 ft (756 m) · hardiness zone 4a*

  • Lower-risk planting dateafter June 3only 1 spring in 10 still has a frost later
  • Typical last frostMay 2050% chance of a frost after it
  • Typical first fall frostSeptember 2350% chance of a frost before it
  • Frost-free season124 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season at Pretty Rock, NDSpring: a frost after May 7 in 9 years out of 10, after May 20 in half of the years, after June 3 in 1 year out of 10. Fall: the first frost comes before September 8 in 1 year out of 10, before September 23 in half of the years, before October 5 in 9 years out of 10. Typical frost-free season: 124 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 20First frost ~Sep 23Frost season at Pretty Rock, NDSpring: a frost after May 7 in 9 years out of 10, after May 20 in half of the years, after June 3 in 1 year out of 10. Fall: the first frost comes before September 8 in 1 year out of 10, before September 23 in half of the years, before October 5 in 9 years out of 10. Typical frost-free season: 124 days.JFMAMJJASONDLast frost ~May 20First frost ~Sep 23
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 30 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 3September 8
50% (typical)May 20September 23
90% (likely)May 7October 5
Frost-free season (32°F, 50% chance)
124 days
Hard frost (28°F), last in spring, 50% chance after
May 9
Hard frost (28°F), first in fall, 50% chance before
October 2

The last 15 years (2006–2020 normals)

Typical last frost May 20 (same as the 30-year normal), typical first fall frost September 25 (2 days later). Frost-free season 127 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 Pretty Rock: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 3, 20% May 30, 30% May 26, 40% May 23, 50% May 20, 60% May 17, 70% May 14, 80% May 11, 90% May 7. Observed last spring frost in recent years: 2021 May 27, 2022 June 3, 2023 May 19, 2024 May 4, 2025 May 22, 2026 May 20.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 3May 20May 72021: May 272022: June 32023: May 192024: May 42025: May 222026: May 20Fall at Pretty Rock: chance of a frost before this dateFall, chance of a frost before the date: 10% September 8, 20% September 13, 30% September 17, 40% September 20, 50% September 23, 60% September 26, 70% September 28, 80% October 1, 90% October 5. Observed first fall frost in recent years: 2021 September 25, 2022 September 10, 2023 October 7, 2024 September 22, 2025 September 6.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 8Sep 23Oct 52021: September 252022: September 102023: October 72024: September 222025: September 6
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
2021May 27September 25
2022June 3September 10
2023May 19October 7
2024May 4September 22
2025May 22September 6
2026May 20season not over yet

What these dates mean

September 8 is the cautious fall date for finishing the harvest of tender crops in Pretty Rock, carrying only a 10 % chance that a light frost has arrived earlier. Gardeners who wait until that date reduce the risk of frost damage as the season draws to a close.

The 50% light-frost dates are May 20 in spring and September 23 in fall; each marks the point at which there is an even chance of a frost occurring later (spring) or earlier (fall). For a cautious plan, the spring tender-crop date is June 3, the 10 %-chance date, while the fall cautious date is September 8.

Hard frosts at 28 °F are more damaging than 32 °F light frosts because the lower temperature can cause more severe injury, and the median hard-frost dates are May 9 and October 2.

How to read the probabilities

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

  • Spring: "10% after June 3" 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 8" 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 Pretty Rock, NDNumbered nearest stations: 1 — Lemmon, SD — 22 mi; 2 — Heart Butte Dam, ND — 29 mi; 3 — Hebron, ND — 51 mi; 4 — New Salem, ND — 52 mi; 5 — Bison, SD — 53 mi.SD25 mi · 40 km1. Lemmon, SD — 22 mi12. Heart Butte Dam, ND — 29 mi23. Hebron, ND — 51 mi34. New Salem, ND — 52 mi45. Bison, SD — 53 mi5
  1. Lemmon, SD 22 mi (35 km)
  2. Heart Butte Dam, ND 29 mi (46 km)
  3. Hebron, ND 51 mi (83 km)
  4. New Salem, ND 52 mi (84 km)
  5. Bison, SD 53 mi (86 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: 46.1758, -101.8561.