U.S. Frost Dates by Weather Station

NOAA station USC00323117 · North Dakota

Frost Dates for Forman, ND

NOAA weather station Forman 5 SSE (USC00323117), North Dakota · elevation 1250 ft (381 m) · hardiness zone 4a*

  • Lower-risk planting dateafter May 20only 1 spring in 10 still has a frost later
  • Typical last frostMay 750% chance of a frost after it
  • Typical first fall frostOctober 150% chance of a frost before it
  • Frost-free season146 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season at Forman, NDSpring: a frost after April 24 in 9 years out of 10, after May 7 in half of the years, after May 20 in 1 year out of 10. Fall: the first frost comes before September 18 in 1 year out of 10, before October 1 in half of the years, before October 13 in 9 years out of 10. Typical frost-free season: 146 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 7First frost ~Oct 1Frost season at Forman, NDSpring: a frost after April 24 in 9 years out of 10, after May 7 in half of the years, after May 20 in 1 year out of 10. Fall: the first frost comes before September 18 in 1 year out of 10, before October 1 in half of the years, before October 13 in 9 years out of 10. Typical frost-free season: 146 days.JFMAMJJASONDLast frost ~May 7First frost ~Oct 1
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)May 20September 18
50% (typical)May 7October 1
90% (likely)April 24October 13
Frost-free season (32°F, 50% chance)
146 days
Hard frost (28°F), last in spring, 50% chance after
April 29
Hard frost (28°F), first in fall, 50% chance before
October 9

The last 15 years (2006–2020 normals)

Typical last frost May 7 (same as the 30-year normal), typical first fall frost October 4 (3 days later). Frost-free season 149 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 Forman: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 20, 20% May 16, 30% May 12, 40% May 9, 50% May 7, 60% May 4, 70% May 1, 80% April 29, 90% April 24. Observed last spring frost in recent years: 2021 May 11.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 20May 7Apr 242021: May 11Fall at Forman: chance of a frost before this dateFall, chance of a frost before the date: 10% September 18, 20% September 23, 30% September 26, 40% September 28, 50% October 1, 60% October 2, 70% October 5, 80% October 9, 90% October 13. Observed first fall frost in recent years: 2021 October 15.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 18Oct 1Oct 132021: October 15
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 11October 15
2022no datano data
2023no datano data
2024no datano data
2025no dataincomplete record
2026incomplete recordseason not over yet

What these dates mean

Planting tender crops on the early spring date of April 24 in Forman carries a 90 % chance of frost and is therefore a gamble. The later spring date of May 20 has only a 10 % chance of a frost later than that day, making it the cautious choice for setting out tender crops.

The cautious date for finishing tender crops in the fall is September 18, when there is only a 10 % chance a frost has arrived earlier. Light-frost 50 % dates are May 7 and October 1, marking the point at which a frost is equally likely. Hard-frost 50 % dates are April 29 in spring and October 9 in fall, indicating an even chance of a 28 °F frost on those days.

A hard frost at 28 °F can damage plants that survive a light frost at 32 °F, so it represents a greater risk.

How to read the probabilities

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

  • Spring: "10% after May 20" 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 18" 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 Forman, NDNumbered nearest stations: 1 — Britton, SD — 18 mi; 2 — McLeod, ND — 30 mi; 3 — Sisseton, SD — 37 mi; 4 — Victor, SD — 38 mi; 5 — Fullerton, ND — 39 mi.NDMN25 mi · 40 km1. Britton, SD — 18 mi12. McLeod, ND — 30 mi23. Sisseton, SD — 37 mi34. Victor, SD — 38 mi45. Fullerton, ND — 39 mi5
  1. Britton, SD 18 mi (30 km)
  2. McLeod, ND 30 mi (48 km)
  3. Sisseton, SD 37 mi (59 km)
  4. Victor, SD 38 mi (60 km)
  5. Fullerton, ND 39 mi (64 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: 46.0333, -97.595.