U.S. Frost Dates by Weather Station

NOAA station USC00216287 · Minnesota

Frost Dates for Owatonna, MN

NOAA weather station Owatonna (USC00216287), Minnesota · elevation 1140 ft (348 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 20only 1 spring in 10 still has a frost later
  • Typical last frostMay 550% chance of a frost after it
  • Typical first fall frostOctober 650% chance of a frost before it
  • Frost-free season154 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Owatonna, MNSpring: a frost after April 20 in 9 years out of 10, after May 5 in half of the years, after May 20 in 1 year out of 10. Fall: the first frost comes before September 23 in 1 year out of 10, before October 6 in half of the years, before October 21 in 9 years out of 10. Typical frost-free season: 154 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 5First frost ~Oct 6Frost season at Owatonna, MNSpring: a frost after April 20 in 9 years out of 10, after May 5 in half of the years, after May 20 in 1 year out of 10. Fall: the first frost comes before September 23 in 1 year out of 10, before October 6 in half of the years, before October 21 in 9 years out of 10. Typical frost-free season: 154 days.JFMAMJJASONDLast frost ~May 5First frost ~Oct 6
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 30 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 20September 23
50% (typical)May 5October 6
90% (likely)April 20October 21
Frost-free season (32°F, 50% chance)
154 days
Hard frost (28°F), last in spring, 50% chance after
April 25
Hard frost (28°F), first in fall, 50% chance before
October 18

The last 15 years (2006–2020 normals)

Typical last frost May 4 (1 day earlier than the 30-year normal), typical first fall frost October 11 (5 days later). Frost-free season 160 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 Owatonna: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 20, 20% May 14, 30% May 10, 40% May 8, 50% May 5, 60% May 2, 70% April 30, 80% April 25, 90% April 20. Observed last spring frost in recent years: 2021 May 11, 2022 April 28, 2023 May 3, 2024 April 24, 2025 April 26, 2026 May 12.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 20May 5Apr 202021: May 112022: April 282023: May 32024: April 242025: April 262026: May 12Fall at Owatonna: chance of a frost before this dateFall, chance of a frost before the date: 10% September 23, 20% September 28, 30% October 1, 40% October 4, 50% October 6, 60% October 9, 70% October 12, 80% October 16, 90% October 21. Observed first fall frost in recent years: 2021 October 22, 2022 September 28, 2023 October 10, 2025 October 8.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 23Oct 6Oct 212021: October 222022: September 282023: October 102025: 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 11October 22
2022April 28September 28
2023May 3October 10
2024April 24incomplete record
2025April 26October 8
2026May 12season not over yet

What these dates mean

September 23 is the cautious date to finish harvesting tender crops in Owatonna, when there is only a 10% chance that a light frost has already arrived.

May 5 is the 50% date for light frost in spring; there is a 50% chance of a frost later than this date. May 20 is the cautious date for setting out tender crops, carrying a 10% chance of a later frost, while April 20 would be a gamble with a 90% chance. In fall, October 6 is the 50% date, meaning there is a 50% chance of a frost earlier than this date, and October 21 would be a gamble with a 90% chance of an earlier frost.

Hard frost at 28°F is a more critical threshold than a light frost at 32°F because it can injure plants that survive the milder temperature; the 50% hard-frost dates are April 25 in spring and October 18 in fall.

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 23" 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 Owatonna, MNNumbered nearest stations: 1 — near Waseca, MN — 15 mi; 2 — Zumbrota, MN — 31 mi; 3 — Austin, MN — 33 mi; 4 — Albert Lea, MN — 34 mi; 5 — Rochester, MN — 39 mi.IAWI25 mi · 40 km1. near Waseca, MN — 15 mi12. Zumbrota, MN — 31 mi23. Austin, MN — 33 mi34. Albert Lea, MN — 34 mi45. Rochester, MN — 39 mi5
  1. near Waseca, MN 15 mi (24 km)
  2. Zumbrota, MN 31 mi (50 km)
  3. Austin, MN 33 mi (53 km)
  4. Albert Lea, MN 34 mi (55 km)
  5. Rochester, MN 39 mi (63 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: 44.0975, -93.2317.