U.S. Frost Dates by Weather Station

NOAA station USC00470124 · Wisconsin

Frost Dates near Alma, WI

NOAA weather station Alma Dam 4 (USC00470124), Wisconsin · elevation 670 ft (204 m) · hardiness zone 5a*

Alma is the nearest town to the station (0.6 mi away) in GeoNames (CC BY 4.0). The dates below are measured at the station, not in the town itself.

  • Lower-risk planting dateafter May 9only 1 spring in 10 still has a frost later
  • Typical last frostApril 2850% chance of a frost after it
  • Typical first fall frostOctober 1450% chance of a frost before it
  • Frost-free season168 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season near Alma, WISpring: a frost after April 13 in 9 years out of 10, after April 28 in half of the years, after May 9 in 1 year out of 10. Fall: the first frost comes before September 29 in 1 year out of 10, before October 14 in half of the years, before October 29 in 9 years out of 10. Typical frost-free season: 168 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 28First frost ~Oct 14Frost season near Alma, WISpring: a frost after April 13 in 9 years out of 10, after April 28 in half of the years, after May 9 in 1 year out of 10. Fall: the first frost comes before September 29 in 1 year out of 10, before October 14 in half of the years, before October 29 in 9 years out of 10. Typical frost-free season: 168 days.JFMAMJJASONDLast frost ~Apr 28First frost ~Oct 14
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 9September 29
50% (typical)April 28October 14
90% (likely)April 13October 29
Frost-free season (32°F, 50% chance)
168 days
Hard frost (28°F), last in spring, 50% chance after
April 17
Hard frost (28°F), first in fall, 50% chance before
October 26

The last 15 years (2006–2020 normals)

Typical last frost April 26 (2 days earlier than the 30-year normal), typical first fall frost October 18 (4 days later). Frost-free season 175 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 near Alma: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 9, 20% May 5, 30% May 2, 40% April 30, 50% April 28, 60% April 24, 70% April 22, 80% April 18, 90% April 13. Observed last spring frost in recent years: 2021 April 26, 2022 April 28, 2023 April 18, 2024 April 25, 2025 April 9, 2026 April 21.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 9Apr 28Apr 132021: April 262022: April 282023: April 182024: April 252025: April 92026: April 21Fall near Alma: chance of a frost before this dateFall, chance of a frost before the date: 10% September 29, 20% October 3, 30% October 7, 40% October 11, 50% October 14, 60% October 18, 70% October 21, 80% October 24, 90% October 29. Observed first fall frost in recent years: 2021 October 24, 2022 October 18, 2023 October 29, 2024 October 16, 2025 October 25.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 29Oct 14Oct 292021: October 242022: October 182023: October 292024: October 162025: October 25
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
2021April 26October 24
2022April 28October 18
2023April 18October 29
2024April 25October 16
2025April 9October 25
2026April 21season not over yet

What these dates mean

Setting tender crops on April 13 in the Alma area carries a 90% chance that a light frost will still occur, making it a high-risk gamble. A cautious plan waits until May 9, when only a 10% chance of a later frost remains.

The 50% light-frost dates are April 28 in spring and October 14 in fall; each marks the point where the odds of a frost are even, with a 50% chance of a frost later than April 28 and a 50% chance of a frost earlier than October 14. In fall, the conservative cutoff for finishing tender crops is September 29, which has only a 10% chance that a frost has already arrived, while October 29 is a 90% chance gamble. Hard frosts at 28 °F, whose median dates are April 17 and October 26, can injure plants that survive a 32 °F light frost.

How to read the probabilities

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

  • Spring: "10% after May 9" 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 29" 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 Alma, WINumbered nearest stations: 1 — Theilman, MN — 14 mi; 2 — Mondovi, WI — 20 mi; 3 — near Winona, MN — 21 mi; 4 — near Trempealeau, WI — 33 mi; 5 — Zumbrota, MN — 37 mi.MNWI25 mi · 40 km1. Theilman, MN — 14 mi12. Mondovi, WI — 20 mi23. near Winona, MN — 21 mi34. near Trempealeau, WI — 33 mi45. Zumbrota, MN — 37 mi5
  1. Theilman, MN 14 mi (22 km)
  2. Mondovi, WI 20 mi (33 km)
  3. near Winona, MN 21 mi (33 km)
  4. near Trempealeau, WI 33 mi (53 km)
  5. Zumbrota, MN 37 mi (59 km)

Sources

* Hardiness zone 5a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 44.3269, -91.9194.