U.S. Frost Dates by Weather Station

NOAA station USC00471078 · Wisconsin

Frost Dates for Brodhead, WI

NOAA weather station Brodhead WWTP (USC00471078), Wisconsin · elevation 780 ft (238 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 14only 1 spring in 10 still has a frost later
  • Typical last frostApril 2950% chance of a frost after it
  • Typical first fall frostOctober 1250% chance of a frost before it
  • Frost-free season165 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Brodhead, WISpring: a frost after April 14 in 9 years out of 10, after April 29 in half of the years, after May 14 in 1 year out of 10. Fall: the first frost comes before September 28 in 1 year out of 10, before October 12 in half of the years, before October 25 in 9 years out of 10. Typical frost-free season: 165 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 29First frost ~Oct 12Frost season at Brodhead, WISpring: a frost after April 14 in 9 years out of 10, after April 29 in half of the years, after May 14 in 1 year out of 10. Fall: the first frost comes before September 28 in 1 year out of 10, before October 12 in half of the years, before October 25 in 9 years out of 10. Typical frost-free season: 165 days.JFMAMJJASONDLast frost ~Apr 29First frost ~Oct 12
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 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 14September 28
50% (typical)April 29October 12
90% (likely)April 14October 25
Frost-free season (32°F, 50% chance)
165 days
Hard frost (28°F), last in spring, 50% chance after
April 17
Hard frost (28°F), first in fall, 50% chance before
October 22

The last 15 years (2006–2020 normals)

Typical last frost April 29 (same as the 30-year normal), typical first fall frost October 15 (3 days later). Frost-free season 168 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 Brodhead: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 14, 20% May 7, 30% May 4, 40% May 1, 50% April 29, 60% April 26, 70% April 23, 80% April 19, 90% April 14. Observed last spring frost in recent years: 2021 May 13, 2022 April 28, 2023 April 27, 2024 April 26, 2025 April 17, 2026 May 8.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 14Apr 29Apr 142021: May 132022: April 282023: April 272024: April 262025: April 172026: May 8Fall at Brodhead: chance of a frost before this dateFall, chance of a frost before the date: 10% September 28, 20% October 1, 30% October 5, 40% October 8, 50% October 12, 60% October 14, 70% October 17, 80% October 20, 90% October 25. Observed first fall frost in recent years: 2021 October 22, 2022 October 8, 2023 October 11, 2024 October 16, 2025 October 24.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 28Oct 12Oct 252021: October 222022: October 82023: October 112024: October 162025: October 24
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 13October 22
2022April 28October 8
2023April 27October 11
2024April 26October 16
2025April 17October 24
2026May 8season not over yet

What these dates mean

September 28 is the cautious fall date to finish harvesting tender crops in Brodhead, Wisconsin; only a 10 % chance of a light frost has occurred by that day. October 12 is the 50 % date for light frost in the fall, the moment when the probability of a frost having already occurred is 50 %. A hard frost at 28 °F is marked by the 50 % date of October 22, indicating a one-in-two chance of such a freeze.

In spring, the cautious date for setting out tender crops is May 14, when a light frost later than that date has only a 10 % chance. April 29 is the 50 % spring light-frost date, the point at which a frost is equally likely to occur later than that date. The hard-frost 50 % date of April 17 signals a 50 % chance of a 28 °F freeze. A hard frost can injure plants that survive a light frost, so it represents a greater risk.

How to read the probabilities

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

  • Spring: "10% after May 14" 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 28" 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 Brodhead, WINumbered nearest stations: 1 — near Janesville, WI — 16 mi; 2 — Beloit, WI — 20 mi; 3 — Freeport, IL — 25 mi; 4 — UW Arboretum - Madison, WI — 29 mi; 5 — Charmany Farm, WI — 31 mi.ILIA25 mi · 40 km1. near Janesville, WI — 16 mi12. Beloit, WI — 20 mi23. Freeport, IL — 25 mi34. UW Arboretum - Madison, WI — 29 mi45. Charmany Farm, WI — 31 mi5
  1. near Janesville, WI 16 mi (26 km)
  2. Beloit, WI 20 mi (32 km)
  3. Freeport, IL 25 mi (40 km)
  4. UW Arboretum - Madison, WI 29 mi (47 km)
  5. Charmany Farm, WI 31 mi (50 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: 42.6181, -89.3867.