U.S. Frost Dates by Weather Station

NOAA station USC00210939 · Minnesota

Frost Dates for Brainerd, MN

NOAA weather station Brainerd (USC00210939), Minnesota · elevation 1180 ft (360 m) · hardiness zone 4a*

  • Lower-risk planting dateafter May 21only 1 spring in 10 still has a frost later
  • Typical last frostMay 850% chance of a frost after it
  • Typical first fall frostSeptember 2950% chance of a frost before it
  • Frost-free season141 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season at Brainerd, MNSpring: a frost after April 28 in 9 years out of 10, after May 8 in half of the years, after May 21 in 1 year out of 10. Fall: the first frost comes before September 16 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: 141 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 8First frost ~Sep 29Frost season at Brainerd, MNSpring: a frost after April 28 in 9 years out of 10, after May 8 in half of the years, after May 21 in 1 year out of 10. Fall: the first frost comes before September 16 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: 141 days.JFMAMJJASONDLast frost ~May 8First 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 21September 16
50% (typical)May 8September 29
90% (likely)April 28October 11
Frost-free season (32°F, 50% chance)
141 days
Hard frost (28°F), last in spring, 50% chance after
April 30
Hard frost (28°F), first in fall, 50% chance before
October 8

The last 15 years (2006–2020 normals)

Typical last frost May 6 (2 days earlier than the 30-year normal), typical first fall frost October 4 (5 days later). Frost-free season 147 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 Brainerd: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 21, 20% May 16, 30% May 13, 40% May 10, 50% May 8, 60% May 5, 70% May 3, 80% May 1, 90% April 28. Observed last spring frost in recent years: 2021 May 29, 2022 April 29, 2023 April 28, 2024 April 25, 2025 May 4, 2026 May 20.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 21May 8Apr 282021: May 292022: April 292023: April 282024: April 252025: May 42026: May 20Fall at Brainerd: chance of a frost before this dateFall, chance of a frost before the date: 10% September 16, 20% September 21, 30% September 24, 40% September 27, 50% September 29, 60% October 1, 70% October 4, 80% October 7, 90% October 11. Observed first fall frost in recent years: 2021 October 17, 2022 September 28, 2023 October 9, 2024 October 4, 2025 October 8.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 16Sep 29Oct 112021: October 172022: September 282023: October 92024: October 42025: 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 29October 17
2022April 29September 28
2023April 28October 9
2024April 25October 4
2025May 4October 8
2026May 20season not over yet

What these dates mean

May 21 is the cautious spring date, letting a gardener plan to set out tender crops with only a 10% chance of a later light frost. The 50% date is May 8, meaning a 50% chance of a light frost later than this date. In the fall, September 16 is the cautious date for finishing harvest of tender crops, carrying a 10% chance of an earlier light frost, and the 50% date is September 29, meaning a 50% chance of a light frost earlier than this date.

Hard-frost thresholds are lower; the 50% hard-frost dates are April 30 in spring and October 8 in fall, and a hard frost at 28 °F can damage or kill vegetation that survives a light frost at 32 °F.

The span between the two 32°F 50% dates is 141 days, and the record comprises 28 years of observations, giving a solid statistical basis for these probabilities.

How to read the probabilities

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

  • Spring: "10% after May 21" 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 16" 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 Brainerd, MNNumbered nearest stations: 1 — near East Gull Lake, MN — 9 mi; 2 — near Crosslake, MN — 23 mi; 3 — Long Prairie, MN — 42 mi; 4 — near Collegeville, MN — 54 mi; 5 — Mora, MN — 54 mi.MNWI25 mi · 40 km1. near East Gull Lake, MN — 9 mi12. near Crosslake, MN — 23 mi23. Long Prairie, MN — 42 mi34. near Collegeville, MN — 54 mi45. Mora, MN — 54 mi5
  1. near East Gull Lake, MN 9 mi (14 km)
  2. near Crosslake, MN 23 mi (37 km)
  3. Long Prairie, MN 42 mi (67 km)
  4. near Collegeville, MN 54 mi (86 km)
  5. Mora, MN 54 mi (86 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: 46.3433, -94.2086.