U.S. Frost Dates by Weather Station

NOAA station USC00218227 · Minnesota

Frost Dates for Theilman, MN

NOAA weather station Theilman 1 SSW (USC00218227), Minnesota · elevation 753 ft (230 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 22only 1 spring in 10 still has a frost later
  • Typical last frostMay 750% chance of a frost after it
  • Typical first fall frostOctober 250% chance of a frost before it
  • Frost-free season148 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Theilman, MNSpring: a frost after April 24 in 9 years out of 10, after May 7 in half of the years, after May 22 in 1 year out of 10. Fall: the first frost comes before September 20 in 1 year out of 10, before October 2 in half of the years, before October 15 in 9 years out of 10. Typical frost-free season: 148 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 7First frost ~Oct 2Frost season at Theilman, MNSpring: a frost after April 24 in 9 years out of 10, after May 7 in half of the years, after May 22 in 1 year out of 10. Fall: the first frost comes before September 20 in 1 year out of 10, before October 2 in half of the years, before October 15 in 9 years out of 10. Typical frost-free season: 148 days.JFMAMJJASONDLast frost ~May 7First frost ~Oct 2
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 26 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 22September 20
50% (typical)May 7October 2
90% (likely)April 24October 15
Frost-free season (32°F, 50% chance)
148 days
Hard frost (28°F), last in spring, 50% chance after
April 28
Hard frost (28°F), first in fall, 50% chance before
October 12

The last 15 years (2006–2020 normals)

Typical last frost May 5 (2 days earlier than the 30-year normal), typical first fall frost October 7 (5 days later). Frost-free season 154 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 Theilman: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 22, 20% May 15, 30% May 12, 40% May 9, 50% May 7, 60% May 4, 70% May 2, 80% April 29, 90% April 24. Observed last spring frost in recent years: 2021 May 12, 2022 May 23, 2023 May 3, 2024 April 25, 2025 April 30, 2026 May 11.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 22May 7Apr 242021: May 122022: May 232023: May 32024: April 252025: April 302026: May 11Fall at Theilman: chance of a frost before this dateFall, chance of a frost before the date: 10% September 20, 20% September 24, 30% September 27, 40% September 30, 50% October 2, 60% October 4, 70% October 7, 80% October 10, 90% October 15. Observed first fall frost in recent years: 2021 October 17, 2022 September 28, 2023 October 9, 2024 October 7, 2025 October 8.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 20Oct 2Oct 152021: October 172022: September 282023: October 92024: October 72025: 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 12October 17
2022May 23September 28
2023May 3October 9
2024April 25October 7
2025April 30October 8
2026May 11season not over yet

What these dates mean

Setting out tender crops on the early spring date, April 24, carries a 90% chance of a frost later than that date, making it a high-risk move for Theilman gardeners.

The 50% light-frost dates—May 7 in spring and October 2 in fall—are the points at which the odds of a frost later (spring) or earlier (fall) are exactly even. The 50% hard-frost dates, April 28 and October 12, mark the same median odds for temperatures of 28 °F. For a cautious planting schedule, the spring date to use is May 22, which has only a 10% chance of a later frost, and the fall date to finish tender crops is September 20, which has only a 10% chance of an earlier frost.

A hard frost at 28 °F can damage plants more severely than 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 22" 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 20" 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 Theilman, MNNumbered nearest stations: 1 — near Alma, WI — 14 mi; 2 — Zumbrota, MN — 23 mi; 3 — near Winona, MN — 29 mi; 4 — Rochester, MN — 30 mi; 5 — near Red Wing, MN — 31 mi.MNWI25 mi · 40 km1. near Alma, WI — 14 mi12. Zumbrota, MN — 23 mi23. near Winona, MN — 29 mi34. Rochester, MN — 30 mi45. near Red Wing, MN — 31 mi5
  1. near Alma, WI 14 mi (22 km)
  2. Zumbrota, MN 23 mi (38 km)
  3. near Winona, MN 29 mi (47 km)
  4. Rochester, MN 30 mi (48 km)
  5. near Red Wing, MN 31 mi (49 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: 44.2811, -92.1944.