U.S. Frost Dates by Weather Station

NOAA station USC00472556 · Wisconsin

Frost Dates for Ellsworth, WI

NOAA weather station Ellsworth 1 E (USC00472556), Wisconsin · elevation 1030 ft (314 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 27only 1 spring in 10 still has a frost later
  • Typical last frostMay 1350% chance of a frost after it
  • Typical first fall frostSeptember 2950% chance of a frost before it
  • Frost-free season139 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Ellsworth, WISpring: a frost after April 29 in 9 years out of 10, after May 13 in half of the years, after May 27 in 1 year out of 10. Fall: the first frost comes before September 15 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: 139 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 13First frost ~Sep 29Frost season at Ellsworth, WISpring: a frost after April 29 in 9 years out of 10, after May 13 in half of the years, after May 27 in 1 year out of 10. Fall: the first frost comes before September 15 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: 139 days.JFMAMJJASONDLast frost ~May 13First 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.Today

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 27September 15
50% (typical)May 13September 29
90% (likely)April 29October 11
Frost-free season (32°F, 50% chance)
139 days
Hard frost (28°F), last in spring, 50% chance after
May 2
Hard frost (28°F), first in fall, 50% chance before
October 8

The last 15 years (2006–2020 normals)

Typical last frost May 11 (2 days earlier than the 30-year normal), typical first fall frost October 4 (5 days later). Frost-free season 143 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 Ellsworth: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 27, 20% May 22, 30% May 19, 40% May 16, 50% May 13, 60% May 10, 70% May 7, 80% May 3, 90% April 29. Observed last spring frost in recent years: 2021 May 13, 2022 May 5, 2023 May 3, 2024 April 25, 2025 May 1, 2026 May 8.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 27May 13Apr 292021: May 132022: May 52023: May 32024: April 252025: May 12026: May 8Fall at Ellsworth: chance of a frost before this dateFall, chance of a frost before the date: 10% September 15, 20% September 20, 30% September 24, 40% September 27, 50% September 29, 60% October 2, 70% October 5, 80% October 7, 90% October 11. Observed first fall frost in recent years: 2021 October 22, 2022 September 28, 2023 October 17, 2024 October 16, 2025 October 8.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 15Sep 29Oct 112021: October 222022: September 282023: October 172024: October 162025: 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 13October 22
2022May 5September 28
2023May 3October 17
2024April 25October 16
2025May 1October 8
2026May 8season not over yet

What these dates mean

Ellsworth’s 32°F 50% dates—May 13 in spring and September 29 in fall—create a 139-day span that defines the core period for tender crops. The May 13 date marks the point where there is an even chance of a light frost later, while September 29 marks the point where there is an even chance of a light frost earlier. Gardeners can use these median points to understand the middle of the frost risk window.

For a cautious approach, the spring LATE date of May 27 carries only a 10% chance of a frost later, making it the recommended time to set out tender crops. In the fall, the EARLY date of September 15 holds a 10% chance of a frost earlier, serving as the prudent endpoint for harvesting tender crops. A hard frost at 28°F—reflected by the 50% dates of May 2 and October 8—can damage plant tissue that usually survives a light frost at 32°F, so those dates are especially significant.

How to read the probabilities

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

  • Spring: "10% after May 27" 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 15" 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 Ellsworth, WINumbered nearest stations: 1 — near Red Wing, MN — 11 mi; 2 — River Falls, WI — 11 mi; 3 — near Hastings, MN — 20 mi; 4 — Menomonie, WI — 27 mi; 5 — Rosemount, MN — 31 mi.25 mi · 40 km1. near Red Wing, MN — 11 mi12. River Falls, WI — 11 mi23. near Hastings, MN — 20 mi34. Menomonie, WI — 27 mi45. Rosemount, MN — 31 mi5
  1. near Red Wing, MN 11 mi (18 km)
  2. River Falls, WI 11 mi (18 km)
  3. near Hastings, MN 20 mi (33 km)
  4. Menomonie, WI 27 mi (44 km)
  5. Rosemount, MN 31 mi (51 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: 44.7303, -92.4586.