U.S. Frost Dates by Weather Station

NOAA station USC00320382 · North Dakota

Frost Dates for Ashley, ND

NOAA weather station Ashley (USC00320382), North Dakota · elevation 2014 ft (614 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 26only 1 spring in 10 still has a frost later
  • Typical last frostMay 1350% chance of a frost after it
  • Typical first fall frostSeptember 2850% chance of a frost before it
  • Frost-free season137 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Ashley, NDSpring: a frost after May 1 in 9 years out of 10, after May 13 in half of the years, after May 26 in 1 year out of 10. Fall: the first frost comes before September 15 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: 137 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 13First frost ~Sep 28Frost season at Ashley, NDSpring: a frost after May 1 in 9 years out of 10, after May 13 in half of the years, after May 26 in 1 year out of 10. Fall: the first frost comes before September 15 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: 137 days.JFMAMJJASONDLast frost ~May 13First 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.

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 26September 15
50% (typical)May 13September 28
90% (likely)May 1October 10
Frost-free season (32°F, 50% chance)
137 days
Hard frost (28°F), last in spring, 50% chance after
May 5
Hard frost (28°F), first in fall, 50% chance before
October 4

The last 15 years (2006–2020 normals)

Typical last frost May 11 (2 days earlier than the 30-year normal), typical first fall frost October 4 (6 days later). Frost-free season 144 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 Ashley: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 26, 20% May 21, 30% May 18, 40% May 15, 50% May 13, 60% May 10, 70% May 7, 80% May 4, 90% May 1. Observed last spring frost in recent years: 2021 May 29, 2022 May 3, 2023 May 2, 2024 April 29, 2025 May 22.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 26May 13May 12021: May 292022: May 32023: May 22024: April 292025: May 22Fall at Ashley: chance of a frost before this dateFall, chance of a frost before the date: 10% September 15, 20% September 19, 30% September 23, 40% September 25, 50% September 28, 60% September 30, 70% October 2, 80% October 5, 90% October 10. Observed first fall frost in recent years: 2021 October 21, 2022 October 7, 2023 October 7, 2024 October 14, 2025 October 13.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 15Sep 28Oct 102021: October 212022: October 72023: October 72024: October 142025: October 13
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 29October 21
2022May 3October 7
2023May 2October 7
2024April 29October 14
2025May 22October 13
2026incomplete recordseason not over yet

What these dates mean

The 137 days between the 50% dates of May 13 and September 28 in Ashley outline the span during which a light frost (32°F) is less likely than not.

The 50% dates themselves are not frost dates; they simply mark the point where the chance of a light frost is even. For a cautious spring schedule, the date with a 10% chance of frost later is May 26, while planting on May 1 carries a 90% chance of a frost and is a gamble. In the fall, the cautious date to finish tender crops is September 15, which has a 10% chance of a frost earlier, whereas aiming for October 10 involves a 90% chance of an early frost.

Hard frosts, recorded at 28°F on May 5 and October 4, can damage plants more severely than the 32°F light frosts.

How to read the probabilities

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

  • Spring: "10% after May 26" 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 15" 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 Ashley, NDNumbered nearest stations: 1 — Napoleon, ND — 37 mi; 2 — Roscoe, SD — 41 mi; 3 — Ipswich, SD — 44 mi; 4 — Pollock, SD — 45 mi; 5 — Streeter, ND — 47 mi.SD25 mi · 40 km1. Napoleon, ND — 37 mi12. Roscoe, SD — 41 mi23. Ipswich, SD — 44 mi34. Pollock, SD — 45 mi45. Streeter, ND — 47 mi5
  1. Napoleon, ND 37 mi (60 km)
  2. Roscoe, SD 41 mi (65 km)
  3. Ipswich, SD 44 mi (71 km)
  4. Pollock, SD 45 mi (72 km)
  5. Streeter, ND 47 mi (75 km)

Sources

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

Station coordinates: 46.0406, -99.3742.