U.S. Frost Dates by Weather Station

NOAA station USC00478027 · Wisconsin

Frost Dates for Spooner, WI

NOAA weather station Spooner Agricultural Research Station (USC00478027), Wisconsin · elevation 1100 ft (335 m) · hardiness zone 4a*

  • Lower-risk planting dateafter May 29only 1 spring in 10 still has a frost later
  • Typical last frostMay 1450% chance of a frost after it
  • Typical first fall frostSeptember 2850% chance of a frost before it
  • Frost-free season135 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season at Spooner, WISpring: a frost after April 30 in 9 years out of 10, after May 14 in half of the years, after May 29 in 1 year out of 10. Fall: the first frost comes before September 14 in 1 year out of 10, before September 28 in half of the years, before October 11 in 9 years out of 10. Typical frost-free season: 135 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 14First frost ~Sep 28Frost season at Spooner, WISpring: a frost after April 30 in 9 years out of 10, after May 14 in half of the years, after May 29 in 1 year out of 10. Fall: the first frost comes before September 14 in 1 year out of 10, before September 28 in half of the years, before October 11 in 9 years out of 10. Typical frost-free season: 135 days.JFMAMJJASONDLast frost ~May 14First frost ~Sep 28
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 29September 14
50% (typical)May 14September 28
90% (likely)April 30October 11
Frost-free season (32°F, 50% chance)
135 days
Hard frost (28°F), last in spring, 50% chance after
May 2
Hard frost (28°F), first in fall, 50% chance before
October 7

The last 15 years (2006–2020 normals)

Typical last frost May 12 (2 days earlier than the 30-year normal), typical first fall frost October 2 (4 days later). Frost-free season 141 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 Spooner: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 29, 20% May 25, 30% May 21, 40% May 17, 50% May 14, 60% May 10, 70% May 7, 80% May 4, 90% April 30. Observed last spring frost in recent years: 2021 May 29, 2022 May 4, 2023 May 3, 2024 May 10, 2025 April 26, 2026 May 15.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 29May 14Apr 302021: May 292022: May 42023: May 32024: May 102025: April 262026: May 15Fall at Spooner: chance of a frost before this dateFall, chance of a frost before the date: 10% September 14, 20% September 19, 30% September 22, 40% September 25, 50% September 28, 60% October 1, 70% October 3, 80% October 7, 90% October 11. Observed first fall frost in recent years: 2021 October 17, 2022 September 28, 2023 October 9, 2024 October 4, 2025 October 8.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 14Sep 28Oct 112021: October 172022: September 282023: October 92024: October 42025: 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 29October 17
2022May 4September 28
2023May 3October 9
2024May 10October 4
2025April 26October 8
2026May 15season not over yet

What these dates mean

May 29 is the cautious spring date for Spooner; with only a 10 % chance of a light frost later, it lets a gardener set out tender crops with a low risk of frost damage. The earlier spring date, April 30, carries a 90 % chance of frost and is a gamble, while the 50 % date is May 14, meaning there is an even chance of a frost later than that day.

In the fall, September 14 is the cautious date, offering just a 10 % chance that a light frost has arrived earlier, so it marks a prudent time to finish harvesting tender crops. The 50 % date, September 28, indicates an even odds of a frost earlier than that point, and the risky late date, October 11, has a 90 % chance of frost already occurring.

Hard-frost thresholds are more critical because a temperature of 28 °F can kill plants that survive a 32 °F light frost; the 50 % hard-frost dates are May 2 in spring and October 7 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 29" 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 14" 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 Spooner, WINumbered nearest stations: 1 — Cumberland, WI — 21 mi; 2 — Rice Lake, WI — 29 mi; 3 — Gordon, WI — 29 mi; 4 — Luck, WI — 34 mi; 5 — Grantsburg, WI — 39 mi.WIMN25 mi · 40 km1. Cumberland, WI — 21 mi12. Rice Lake, WI — 29 mi23. Gordon, WI — 29 mi34. Luck, WI — 34 mi45. Grantsburg, WI — 39 mi5
  1. Cumberland, WI 21 mi (34 km)
  2. Rice Lake, WI 29 mi (46 km)
  3. Gordon, WI 29 mi (47 km)
  4. Luck, WI 34 mi (55 km)
  5. Grantsburg, WI 39 mi (63 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: 45.8236, -91.8761.