U.S. Frost Dates by Weather Station

NOAA station USC00324102 · North Dakota

Frost Dates for Hebron, ND

NOAA weather station Hebron (USC00324102), North Dakota · elevation 2160 ft (658 m) · hardiness zone 4a*

  • Lower-risk planting dateafter June 2only 1 spring in 10 still has a frost later
  • Typical last frostMay 1950% chance of a frost after it
  • Typical first fall frostSeptember 2150% chance of a frost before it
  • Frost-free season123 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season at Hebron, NDSpring: a frost after May 7 in 9 years out of 10, after May 19 in half of the years, after June 2 in 1 year out of 10. Fall: the first frost comes before September 7 in 1 year out of 10, before September 21 in half of the years, before October 4 in 9 years out of 10. Typical frost-free season: 123 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 19First frost ~Sep 21Frost season at Hebron, NDSpring: a frost after May 7 in 9 years out of 10, after May 19 in half of the years, after June 2 in 1 year out of 10. Fall: the first frost comes before September 7 in 1 year out of 10, before September 21 in half of the years, before October 4 in 9 years out of 10. Typical frost-free season: 123 days.JFMAMJJASONDLast frost ~May 19First frost ~Sep 21
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.

Frost dates (32°F)

Probability of frost, based on 26 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 2September 7
50% (typical)May 19September 21
90% (likely)May 7October 4
Frost-free season (32°F, 50% chance)
123 days
Hard frost (28°F), last in spring, 50% chance after
May 10
Hard frost (28°F), first in fall, 50% chance before
September 30

The last 15 years (2006–2020 normals)

Typical last frost May 20 (1 day later than the 30-year normal), typical first fall frost September 27 (6 days later). Frost-free season 128 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 Hebron: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 2, 20% May 28, 30% May 25, 40% May 21, 50% May 19, 60% May 16, 70% May 14, 80% May 11, 90% May 7. Observed last spring frost in recent years: 2021 May 31, 2022 June 3, 2024 May 25.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 2May 19May 72021: May 312022: June 32024: May 25Fall at Hebron: chance of a frost before this dateFall, chance of a frost before the date: 10% September 7, 20% September 11, 30% September 15, 40% September 19, 50% September 21, 60% September 24, 70% September 27, 80% September 30, 90% October 4. Observed first fall frost in recent years: 2022 September 22, 2023 October 7, 2024 September 22.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 7Sep 21Oct 42022: September 222023: October 72024: September 22
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 31incomplete record
2022June 3September 22
2023incomplete recordOctober 7
2024May 25September 22
2025no datano data
2026no dataseason not over yet

What these dates mean

June 2 is the cautious spring light-frost date for Hebron; only a 10 % chance of a frost later means a gardener can safely set out tender crops after that day. The 50 % spring date, May 19, marks the point where a light frost is equally likely to occur later or not, while the 50 % fall date, September 21, represents an even chance of a frost having arrived earlier.

For a cautious fall plan, the September 7 date carries only a 10 % chance that a frost has already arrived, so finishing the harvest of tender crops by then keeps risk low. The hard-frost 50 % dates—May 10 in spring and September 30 in fall—show when temperatures of 28 °F are as likely as not, and a hard frost can damage plants more seriously than a light frost because it reaches lower temperatures.

How to read the probabilities

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

  • Spring: "10% after June 2" 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 7" 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 Hebron, NDNumbered nearest stations: 1 — Richardton Abbey, ND — 13 mi; 2 — Heart Butte Dam, ND — 24 mi; 3 — New Salem, ND — 26 mi; 4 — near Dickinson, ND — 37 mi; 5 — New England, ND — 47 mi.ND25 mi · 40 km1. Richardton Abbey, ND — 13 mi12. Heart Butte Dam, ND — 24 mi23. New Salem, ND — 26 mi34. near Dickinson, ND — 37 mi45. New England, ND — 47 mi5
  1. Richardton Abbey, ND 13 mi (21 km)
  2. Heart Butte Dam, ND 24 mi (39 km)
  3. New Salem, ND 26 mi (42 km)
  4. near Dickinson, ND 37 mi (59 km)
  5. New England, ND 47 mi (75 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: 46.9075, -102.0383.