U.S. Frost Dates by Weather Station

NOAA station USC00328872 · North Dakota

Frost Dates for Underwood, ND

NOAA weather station Underwood (USC00328872), North Dakota · elevation 2045 ft (623 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 25only 1 spring in 10 still has a frost later
  • Typical last frostMay 1050% chance of a frost after it
  • Typical first fall frostSeptember 2950% chance of a frost before it
  • Frost-free season139 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Underwood, NDSpring: a frost after April 30 in 9 years out of 10, after May 10 in half of the years, after May 25 in 1 year out of 10. Fall: the first frost comes before September 17 in 1 year out of 10, before September 29 in half of the years, before October 11 in 9 years out of 10. Typical frost-free season: 139 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 10First frost ~Sep 29Frost season at Underwood, NDSpring: a frost after April 30 in 9 years out of 10, after May 10 in half of the years, after May 25 in 1 year out of 10. Fall: the first frost comes before September 17 in 1 year out of 10, before September 29 in half of the years, before October 11 in 9 years out of 10. Typical frost-free season: 139 days.JFMAMJJASONDLast frost ~May 10First frost ~Sep 29
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 28 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 25September 17
50% (typical)May 10September 29
90% (likely)April 30October 11
Frost-free season (32°F, 50% chance)
139 days
Hard frost (28°F), last in spring, 50% chance after
May 2
Hard frost (28°F), first in fall, 50% chance before
October 7

The last 15 years (2006–2020 normals)

Typical last frost May 11 (1 day later than the 30-year normal), typical first fall frost October 4 (5 days later). Frost-free season 146 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 Underwood: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 25, 20% May 19, 30% May 15, 40% May 12, 50% May 10, 60% May 7, 70% May 5, 80% May 3, 90% April 30. Observed last spring frost in recent years: 2021 May 28, 2022 May 21, 2023 May 3, 2024 May 4, 2025 April 30, 2026 May 10.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 25May 10Apr 302021: May 282022: May 212023: May 32024: May 42025: April 302026: May 10Fall at Underwood: chance of a frost before this dateFall, chance of a frost before the date: 10% September 17, 20% September 21, 30% September 24, 40% September 27, 50% September 29, 60% October 1, 70% October 3, 80% October 7, 90% October 11. Observed first fall frost in recent years: 2021 October 15, 2022 October 7, 2024 October 14, 2025 October 6.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 17Sep 29Oct 112021: October 152022: October 72024: October 142025: October 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 28October 15
2022May 21October 7
2023May 3incomplete record
2024May 4October 14
2025April 30October 6
2026May 10season not over yet

What these dates mean

Planting tender crops on the early spring date of April 30 in Underwood is a gamble, because there is a 90% chance that a light frost will occur later that season. The 50% dates give a sense of even odds: the 50% date is May 10 for spring light frost, and the 50% date is September 29 for fall light frost. For hard frost the median dates are May 2 in spring and October 7 in fall. A hard frost at 28 °F can damage plants that would otherwise survive a 32 °F light frost. Gardeners who prefer a cautious approach would wait until the May 25 light-frost date, which carries only a 10% chance of a later frost, and would finish tender crops by September 17, the fall date with a 10% chance that a frost has already arrived.

How to read the probabilities

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

  • Spring: "10% after May 25" 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 17" 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 Underwood, NDNumbered nearest stations: 1 — Turtle Lake, ND — 13 mi; 2 — Garrison, ND — 19 mi; 3 — Max, ND — 26 mi; 4 — McClusky, ND — 33 mi; 5 — New Salem, ND — 42 mi.25 mi · 40 km1. Turtle Lake, ND — 13 mi12. Garrison, ND — 19 mi23. Max, ND — 26 mi34. McClusky, ND — 33 mi45. New Salem, ND — 42 mi5
  1. Turtle Lake, ND 13 mi (21 km)
  2. Garrison, ND 19 mi (30 km)
  3. Max, ND 26 mi (42 km)
  4. McClusky, ND 33 mi (53 km)
  5. New Salem, ND 42 mi (68 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: 47.455, -101.1461.