U.S. Frost Dates by Weather Station

NOAA station USC00477464 · Wisconsin

Frost Dates for St. Croix Falls, WI

NOAA weather station St. Croix Falls (USC00477464), Wisconsin · elevation 750 ft (229 m) · hardiness zone 4a*

  • Lower-risk planting dateafter May 18only 1 spring in 10 still has a frost later
  • Typical last frostMay 450% chance of a frost after it
  • Typical first fall frostOctober 850% chance of a frost before it
  • Frost-free season156 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season at St. Croix Falls, WISpring: a frost after April 20 in 9 years out of 10, after May 4 in half of the years, after May 18 in 1 year out of 10. Fall: the first frost comes before September 24 in 1 year out of 10, before October 8 in half of the years, before October 23 in 9 years out of 10. Typical frost-free season: 156 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 4First frost ~Oct 8Frost season at St. Croix Falls, WISpring: a frost after April 20 in 9 years out of 10, after May 4 in half of the years, after May 18 in 1 year out of 10. Fall: the first frost comes before September 24 in 1 year out of 10, before October 8 in half of the years, before October 23 in 9 years out of 10. Typical frost-free season: 156 days.JFMAMJJASONDLast frost ~May 4First frost ~Oct 8
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)May 18September 24
50% (typical)May 4October 8
90% (likely)April 20October 23
Frost-free season (32°F, 50% chance)
156 days
Hard frost (28°F), last in spring, 50% chance after
April 24
Hard frost (28°F), first in fall, 50% chance before
October 20

The last 15 years (2006–2020 normals)

Typical last frost May 2 (2 days earlier than the 30-year normal), typical first fall frost October 15 (7 days later). Frost-free season 163 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 St. Croix Falls: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 18, 20% May 14, 30% May 9, 40% May 6, 50% May 4, 60% May 1, 70% April 29, 80% April 25, 90% April 20. Observed last spring frost in recent years: 2021 May 11, 2022 April 28, 2023 April 27, 2024 April 25, 2025 April 17, 2026 May 3.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 18May 4Apr 202021: May 112022: April 282023: April 272024: April 252025: April 172026: May 3Fall at St. Croix Falls: chance of a frost before this dateFall, chance of a frost before the date: 10% September 24, 20% September 29, 30% October 1, 40% October 5, 50% October 8, 60% October 11, 70% October 14, 80% October 18, 90% October 23. Observed first fall frost in recent years: 2021 October 17, 2022 October 8, 2023 October 28, 2024 October 14, 2025 October 23.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 24Oct 8Oct 232021: October 172022: October 82023: October 282024: October 142025: October 23
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 11October 17
2022April 28October 8
2023April 27October 28
2024April 25October 14
2025April 17October 23
2026May 3season not over yet

What these dates mean

September 24 is the cautious fall date for finishing the harvest in St. Croix Falls, because only a 10 % chance of a light frost has occurred earlier.

In spring the cautious date for setting out tender crops is May 18, when the chance of a light frost later falls to 10 %; the early spring gamble is April 20 with a 90 % chance. The median 32°F dates are May 4 and October 8; each marks the point where a light frost is equally likely to have happened or not. The hard-frost median dates are April 24 in spring and October 20 in fall, indicating when a 28°F frost is equally probable.

A hard frost matters more than a light frost because the lower temperature can damage plant tissue that survives the milder 32°F event.

How to read the probabilities

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

  • Spring: "10% after May 18" 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 24" 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 St. Croix Falls, WINumbered nearest stations: 1 — Wild River State Park, MN — 9 mi; 2 — Forest Lake, MN — 13 mi; 3 — Luck, WI — 14 mi; 4 — Amery, WI — 16 mi; 5 — Grantsburg, WI — 25 mi.WIMN25 mi · 40 km1. Wild River State Park, MN — 9 mi12. Forest Lake, MN — 13 mi23. Luck, WI — 14 mi34. Amery, WI — 16 mi45. Grantsburg, WI — 25 mi5
  1. Wild River State Park, MN 9 mi (15 km)
  2. Forest Lake, MN 13 mi (22 km)
  3. Luck, WI 14 mi (22 km)
  4. Amery, WI 16 mi (25 km)
  5. Grantsburg, WI 25 mi (40 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: 45.4117, -92.6467.