U.S. Frost Dates by Weather Station

NOAA station USC00479304 · Wisconsin

Frost Dates for Winter, WI

NOAA weather station Winter (USC00479304), Wisconsin · elevation 1355 ft (413 m) · hardiness zone 4a*

  • Lower-risk planting dateafter June 3only 1 spring in 10 still has a frost later
  • Typical last frostMay 1950% chance of a frost after it
  • Typical first fall frostSeptember 2750% chance of a frost before it
  • Frost-free season129 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season at Winter, WISpring: a frost after May 3 in 9 years out of 10, after May 19 in half of the years, after June 3 in 1 year out of 10. Fall: the first frost comes before September 8 in 1 year out of 10, before September 27 in half of the years, before October 8 in 9 years out of 10. Typical frost-free season: 129 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 19First frost ~Sep 27Frost season at Winter, WISpring: a frost after May 3 in 9 years out of 10, after May 19 in half of the years, after June 3 in 1 year out of 10. Fall: the first frost comes before September 8 in 1 year out of 10, before September 27 in half of the years, before October 8 in 9 years out of 10. Typical frost-free season: 129 days.JFMAMJJASONDLast frost ~May 19First frost ~Sep 27
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 27 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 3September 8
50% (typical)May 19September 27
90% (likely)May 3October 8
Frost-free season (32°F, 50% chance)
129 days
Hard frost (28°F), last in spring, 50% chance after
May 6
Hard frost (28°F), first in fall, 50% chance before
October 5

The last 15 years (2006–2020 normals)

Typical last frost May 19 (same as the 30-year normal), typical first fall frost September 26 (1 day earlier). Frost-free season 128 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 Winter: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 3, 20% May 29, 30% May 26, 40% May 22, 50% May 19, 60% May 16, 70% May 13, 80% May 8, 90% May 3.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 3May 19May 3Fall at Winter: chance of a frost before this dateFall, chance of a frost before the date: 10% September 8, 20% September 15, 30% September 20, 40% September 24, 50% September 27, 60% September 30, 70% October 2, 80% October 5, 90% October 8.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 8Sep 27Oct 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.

What these dates mean

September 8 is the cautious fall date in Winter, marking the point at which there is only a 10 % chance a light frost has arrived, and it signals when tender crops should be finished.

The 50% spring light-frost date is May 19; at that moment the odds of a frost later are equal to the odds of none. The 50% fall light-frost date is September 27, with an even chance of a frost earlier. The median hard-frost dates are May 6 in spring and October 5 in fall, indicating when a 28 °F frost is equally likely to have occurred or not.

For a cautious plan, tender crops should be set out after the June 3 spring date, which carries a 10 % chance of frost later, and should be harvested by September 8 in fall, which carries a 10 % chance of frost earlier. Hard frost at 28 °F can injure plants that survive a light frost at 32 °F, making it the more critical temperature threshold.

How to read the probabilities

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

  • Spring: "10% after June 3" 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 8" 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 Winter, WINumbered nearest stations: 1 — Spooner, WI — 42 mi; 2 — Rice Lake, WI — 46 mi; 3 — Gordon, WI — 50 mi; 4 — Cumberland, WI — 53 mi; 5 — Bloomer, WI — 54 mi.WIMNMI25 mi · 40 km1. Spooner, WI — 42 mi12. Rice Lake, WI — 46 mi23. Gordon, WI — 50 mi34. Cumberland, WI — 53 mi45. Bloomer, WI — 54 mi5
  1. Spooner, WI 42 mi (68 km)
  2. Rice Lake, WI 46 mi (74 km)
  3. Gordon, WI 50 mi (80 km)
  4. Cumberland, WI 53 mi (85 km)
  5. Bloomer, WI 54 mi (88 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: 45.7992, -90.9947.