U.S. Frost Dates by Weather Station

NOAA station USC00329445 · North Dakota

Frost Dates for Willow City, ND

NOAA weather station Willow City (USC00329445), North Dakota · elevation 1473 ft (449 m) · hardiness zone 3b*

  • Lower-risk planting dateafter June 1only 1 spring in 10 still has a frost later
  • Typical last frostMay 2150% chance of a frost after it
  • Typical first fall frostSeptember 2050% chance of a frost before it
  • Frost-free season119 daystypical year, 32°F
  • Hardiness zone3bcalculated*

The year at a glance

Frost season at Willow City, NDSpring: a frost after May 11 in 9 years out of 10, after May 21 in half of the years, after June 1 in 1 year out of 10. Fall: the first frost comes before September 5 in 1 year out of 10, before September 20 in half of the years, before October 1 in 9 years out of 10. Typical frost-free season: 119 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 21First frost ~Sep 20Frost season at Willow City, NDSpring: a frost after May 11 in 9 years out of 10, after May 21 in half of the years, after June 1 in 1 year out of 10. Fall: the first frost comes before September 5 in 1 year out of 10, before September 20 in half of the years, before October 1 in 9 years out of 10. Typical frost-free season: 119 days.JFMAMJJASONDLast frost ~May 21First 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 5
50% (typical)May 21September 20
90% (likely)May 11October 1
Frost-free season (32°F, 50% chance)
119 days
Hard frost (28°F), last in spring, 50% chance after
May 13
Hard frost (28°F), first in fall, 50% chance before
September 27

The last 15 years (2006–2020 normals)

Typical last frost May 18 (3 days earlier than the 30-year normal), typical first fall frost September 21 (1 day later). Frost-free season 125 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 Willow City: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 1, 20% May 29, 30% May 26, 40% May 23, 50% May 21, 60% May 19, 70% May 17, 80% May 14, 90% May 11. Observed last spring frost in recent years: 2021 June 1, 2022 May 3, 2023 May 3.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 1May 21May 112021: June 12022: May 32023: May 3Fall at Willow City: chance of a frost before this dateFall, chance of a frost before the date: 10% September 5, 20% September 11, 30% September 14, 40% September 17, 50% September 20, 60% September 22, 70% September 24, 80% September 26, 90% October 1. Observed first fall frost in recent years: 2021 October 16, 2022 September 22, 2024 October 2.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 5Sep 20Oct 12021: October 162022: September 222024: October 2
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
2021June 1October 16
2022May 3September 22
2023May 3incomplete record
2024incomplete recordOctober 2
2025incomplete recordno data
2026incomplete recordseason not over yet

What these dates mean

The 119 days between the 50% dates in Willow City define the window where a light frost is about as likely to have passed as to still occur. The median spring light-frost date is May 21, meaning there is a 50 % chance of a light frost later than that point, and the median fall light-frost date is September 20, meaning there is a 50 % chance of a light frost earlier than that point.

For a cautious spring schedule, gardeners can wait until the June 1 date, which carries only a 10 % chance of a light frost later, while in fall the September 5 date offers a 10 % chance of a light frost earlier. The hard-frost median dates are May 13 and September 27; a hard frost at 28 °F can damage plant tissue that would survive a light frost at 32 °F.

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 5" 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 Willow City, NDNumbered nearest stations: 1 — Bottineau, ND — 17 mi; 2 — Towner, ND — 17 mi; 3 — Upham, ND — 20 mi; 4 — Rugby, ND — 22 mi; 5 — Drake, ND — 39 mi.25 mi · 40 km1. Bottineau, ND — 17 mi12. Towner, ND — 17 mi23. Upham, ND — 20 mi34. Rugby, ND — 22 mi45. Drake, ND — 39 mi5
  1. Bottineau, ND 17 mi (27 km)
  2. Towner, ND 17 mi (27 km)
  3. Upham, ND 20 mi (32 km)
  4. Rugby, ND 22 mi (36 km)
  5. Drake, ND 39 mi (62 km)

Sources

* Hardiness zone 3b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 48.6061, -100.2911.