U.S. Frost Dates by Weather Station

NOAA station USC00478349 · Wisconsin

Frost Dates for Superior, WI

NOAA weather station Superior (USC00478349), Wisconsin · elevation 607 ft (185 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 25only 1 spring in 10 still has a frost later
  • Typical last frostMay 650% chance of a frost after it
  • Typical first fall frostOctober 950% chance of a frost before it
  • Frost-free season154 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Superior, WISpring: a frost after April 24 in 9 years out of 10, after May 6 in half of the years, after May 25 in 1 year out of 10. Fall: the first frost comes before September 24 in 1 year out of 10, before October 9 in half of the years, before October 24 in 9 years out of 10. Typical frost-free season: 154 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 6First frost ~Oct 9Frost season at Superior, WISpring: a frost after April 24 in 9 years out of 10, after May 6 in half of the years, after May 25 in 1 year out of 10. Fall: the first frost comes before September 24 in 1 year out of 10, before October 9 in half of the years, before October 24 in 9 years out of 10. Typical frost-free season: 154 days.JFMAMJJASONDLast frost ~May 6First frost ~Oct 9
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 25September 24
50% (typical)May 6October 9
90% (likely)April 24October 24
Frost-free season (32°F, 50% chance)
154 days
Hard frost (28°F), last in spring, 50% chance after
April 24
Hard frost (28°F), first in fall, 50% chance before
October 24

The last 15 years (2006–2020 normals)

Typical last frost May 5 (1 day earlier than the 30-year normal), typical first fall frost October 14 (5 days later). Frost-free season 160 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 Superior: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 25, 20% May 19, 30% May 15, 40% May 10, 50% May 6, 60% May 4, 70% May 1, 80% April 29, 90% April 24. Observed last spring frost in recent years: 2021 May 11, 2022 April 29, 2023 May 3, 2024 April 24, 2025 May 9, 2026 May 11.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 25May 6Apr 242021: May 112022: April 292023: May 32024: April 242025: May 92026: May 11Fall at Superior: chance of a frost before this dateFall, chance of a frost before the date: 10% September 24, 20% September 29, 30% October 2, 40% October 6, 50% October 9, 60% October 12, 70% October 16, 80% October 20, 90% October 24. Observed first fall frost in recent years: 2021 October 23, 2022 September 28, 2023 October 17, 2024 October 16, 2025 October 8.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 24Oct 9Oct 242021: October 232022: 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 11October 23
2022April 29September 28
2023May 3October 17
2024April 24October 16
2025May 9October 8
2026May 11season not over yet

What these dates mean

Setting out tender crops on April 24 is a gamble, carrying a 90% chance that a light frost will still occur later. The cautious approach is to wait until May 25, when only a 10% chance of a later frost remains. For a gardener, the 50% date of May 6 marks the point where a light frost is equally likely to appear later or not, giving a statistical midpoint for planning.

In the autumn, the prudent date to finish harvesting tender crops is September 24, with just a 10% chance that a light frost has already arrived. The fall 50% date of October 9 signals an even odds chance of a frost occurring earlier. A hard frost, recorded at 28 °F, can damage plants more severely than a light frost at 32 °F, so its 50% dates of April 24 and October 24 are important reference points.

How to read the probabilities

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

  • Spring: "10% after May 25" 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 Superior, WINumbered nearest stations: 1 — Cloquet, MN — 21 mi; 2 — Two Harbors, MN — 28 mi; 3 — Gordon, WI — 36 mi; 4 — Bruno, MN — 37 mi; 5 — Moose Lake, MN — 38 mi.MNWI25 mi · 40 km1. Cloquet, MN — 21 mi12. Two Harbors, MN — 28 mi23. Gordon, WI — 36 mi34. Bruno, MN — 37 mi45. Moose Lake, MN — 38 mi5
  1. Cloquet, MN 21 mi (35 km)
  2. Two Harbors, MN 28 mi (45 km)
  3. Gordon, WI 36 mi (57 km)
  4. Bruno, MN 37 mi (59 km)
  5. Moose Lake, MN 38 mi (61 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: 46.7269, -92.0719.