U.S. Frost Dates by Weather Station

NOAA station USC00211374 · Minnesota

Frost Dates for Cass Lake, MN

NOAA weather station Cass Lake (USC00211374), Minnesota · elevation 1296 ft (395 m) · hardiness zone 3b*

  • Lower-risk planting dateafter May 30only 1 spring in 10 still has a frost later
  • Typical last frostMay 1750% chance of a frost after it
  • Typical first fall frostSeptember 2650% chance of a frost before it
  • Frost-free season131 daystypical year, 32°F
  • Hardiness zone3bcalculated*

The year at a glance

Frost season at Cass Lake, MNSpring: a frost after May 3 in 9 years out of 10, after May 17 in half of the years, after May 30 in 1 year out of 10. Fall: the first frost comes before September 12 in 1 year out of 10, before September 26 in half of the years, before October 11 in 9 years out of 10. Typical frost-free season: 131 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 17First frost ~Sep 26Frost season at Cass Lake, MNSpring: a frost after May 3 in 9 years out of 10, after May 17 in half of the years, after May 30 in 1 year out of 10. Fall: the first frost comes before September 12 in 1 year out of 10, before September 26 in half of the years, before October 11 in 9 years out of 10. Typical frost-free season: 131 days.JFMAMJJASONDLast frost ~May 17First frost ~Sep 26
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.Today

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 30September 12
50% (typical)May 17September 26
90% (likely)May 3October 11
Frost-free season (32°F, 50% chance)
131 days
Hard frost (28°F), last in spring, 50% chance after
May 7
Hard frost (28°F), first in fall, 50% chance before
October 6

The last 15 years (2006–2020 normals)

Typical last frost May 16 (1 day earlier than the 30-year normal), typical first fall frost September 30 (4 days later). Frost-free season 135 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 Cass Lake: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 30, 20% May 25, 30% May 22, 40% May 19, 50% May 17, 60% May 14, 70% May 11, 80% May 8, 90% May 3. Observed last spring frost in recent years: 2021 May 28, 2022 May 5, 2023 May 3, 2024 April 24, 2025 May 18, 2026 May 20.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 30May 17May 32021: May 282022: May 52023: May 32024: April 242025: May 182026: May 20Fall at Cass Lake: chance of a frost before this dateFall, chance of a frost before the date: 10% September 12, 20% September 17, 30% September 20, 40% September 23, 50% September 26, 60% September 29, 70% October 2, 80% October 5, 90% October 11. Observed first fall frost in recent years: 2021 October 17, 2022 September 27, 2023 October 9, 2024 October 8, 2025 October 8.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 12Sep 26Oct 112021: October 172022: September 272023: October 92024: October 82025: October 8
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 17
2022May 5September 27
2023May 3October 9
2024April 24October 8
2025May 18October 8
2026May 20season not over yet

What these dates mean

The cautious fall date for finishing the harvest in Cass Lake is September 12, when there is only a 10 % chance that a light frost has arrived earlier. Gardeners who wait until that day can expect a low risk of frost damage to tender crops.

In spring the cautious date for setting out tender crops is May 30, a point with a 10 % chance of a light frost later than that date; planting earlier, such as on May 3, carries a 90 % chance and is a gamble. The 50% dates—May 17 for spring and September 26 for fall—indicate the moment when there is an even odds of a light frost later (spring) or earlier (fall) and are not frost dates themselves. A hard frost at 28 °F, reflected by the median dates May 7 and October 6, can injure plant tissue that survives 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 May 30" 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 12" 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 Cass Lake, MNNumbered nearest stations: 1 — Leech Lake, MN — 21 mi; 2 — Itasca University of Minn, MN — 29 mi; 3 — Park Rapids, MN — 40 mi; 4 — near Grand Rapids, MN — 53 mi; 5 — near Crosslake, MN — 55 mi.MN25 mi · 40 km1. Leech Lake, MN — 21 mi12. Itasca University of Minn, MN — 29 mi23. Park Rapids, MN — 40 mi34. near Grand Rapids, MN — 53 mi45. near Crosslake, MN — 55 mi5
  1. Leech Lake, MN 21 mi (33 km)
  2. Itasca University of Minn, MN 29 mi (47 km)
  3. Park Rapids, MN 40 mi (64 km)
  4. near Grand Rapids, MN 53 mi (86 km)
  5. near Crosslake, MN 55 mi (88 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: 47.3847, -94.6147.