U.S. Frost Dates by Weather Station

NOAA station USC00325813 · North Dakota

Frost Dates for Medora, ND

NOAA weather station Medora (USC00325813), North Dakota · elevation 2268 ft (691 m) · hardiness zone 4a*

  • Lower-risk planting dateafter June 1only 1 spring in 10 still has a frost later
  • Typical last frostMay 1950% chance of a frost after it
  • Typical first fall frostSeptember 2050% chance of a frost before it
  • Frost-free season123 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season at Medora, NDSpring: a frost after May 7 in 9 years out of 10, after May 19 in half of the years, after June 1 in 1 year out of 10. Fall: the first frost comes before September 6 in 1 year out of 10, before September 20 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 20Frost season at Medora, NDSpring: a frost after May 7 in 9 years out of 10, after May 19 in half of the years, after June 1 in 1 year out of 10. Fall: the first frost comes before September 6 in 1 year out of 10, before September 20 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 20
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 27 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 1September 6
50% (typical)May 19September 20
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 8
Hard frost (28°F), first in fall, 50% chance before
September 29

The last 15 years (2006–2020 normals)

Typical last frost May 17 (2 days earlier than the 30-year normal), typical first fall frost September 25 (5 days later). Frost-free season 130 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 Medora: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 1, 20% May 27, 30% May 24, 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: 2024 May 5, 2025 May 23, 2026 May 20.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 1May 19May 72024: May 52025: May 232026: May 20Fall at Medora: chance of a frost before this dateFall, chance of a frost before the date: 10% September 6, 20% September 10, 30% September 15, 40% September 18, 50% September 20, 60% September 23, 70% September 26, 80% September 29, 90% October 4. Observed first fall frost in recent years: 2021 September 12, 2024 September 22.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 6Sep 20Oct 42021: September 122024: 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
2021incomplete recordSeptember 12
2022incomplete recordincomplete record
2023incomplete recordno data
2024May 5September 22
2025May 23incomplete record
2026May 20season not over yet

What these dates mean

June 1 is the cautious spring date for light frost in Medora, with only a 10 % chance of frost later, and it lets a gardener set out tender crops with relatively low risk. The 90 % gamble date of May 7 should be avoided for tender crops.

The 50 % date is May 19, meaning there is an even chance of a frost later, while the 50 % date is September 20, meaning there is an even chance of a frost earlier. September 6 is the cautious fall date, with only a 10 % chance of frost earlier, and it marks a sensible point to finish harvesting tender crops. The 50 % hard-frost date is May 8 and the 50 % hard-frost date is September 29. A hard frost at 28 °F can damage plants more severely than a light frost at 32 °F. Counting on tender crops as late as October 4 carries a 90 % chance of frost and is a gamble.

How to read the probabilities

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

  • Spring: "10% after June 1" 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 6" 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 Medora, NDNumbered nearest stations: 1 — near Dickinson, ND — 35 mi; 2 — Grassy Butte, ND — 37 mi; 3 — Carlyle, MT — 39 mi; 4 — New England, ND — 41 mi; 5 — Bowman, ND — 50 mi.MT25 mi · 40 km1. near Dickinson, ND — 35 mi12. Grassy Butte, ND — 37 mi23. Carlyle, MT — 39 mi34. New England, ND — 41 mi45. Bowman, ND — 50 mi5
  1. near Dickinson, ND 35 mi (57 km)
  2. Grassy Butte, ND 37 mi (59 km)
  3. Carlyle, MT 39 mi (63 km)
  4. New England, ND 41 mi (65 km)
  5. Bowman, ND 50 mi (81 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: 46.9161, -103.5264.