U.S. Frost Dates by Weather Station

NOAA station USC00470273 · Wisconsin

Frost Dates for UW Arboretum - Madison, WI

NOAA weather station UW Arboretum - Madison (USC00470273), Wisconsin · elevation 870 ft (265 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 17only 1 spring in 10 still has a frost later
  • Typical last frostMay 150% chance of a frost after it
  • Typical first fall frostOctober 950% chance of a frost before it
  • Frost-free season161 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at UW Arboretum - Madison, WISpring: a frost after April 18 in 9 years out of 10, after May 1 in half of the years, after May 17 in 1 year out of 10. Fall: the first frost comes before September 26 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: 161 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 1First frost ~Oct 9Frost season at UW Arboretum - Madison, WISpring: a frost after April 18 in 9 years out of 10, after May 1 in half of the years, after May 17 in 1 year out of 10. Fall: the first frost comes before September 26 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: 161 days.JFMAMJJASONDLast frost ~May 1First 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 27 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 17September 26
50% (typical)May 1October 9
90% (likely)April 18October 24
Frost-free season (32°F, 50% chance)
161 days
Hard frost (28°F), last in spring, 50% chance after
April 20
Hard frost (28°F), first in fall, 50% chance before
October 20

The last 15 years (2006–2020 normals)

Typical last frost April 30 (1 day earlier than the 30-year normal), typical first fall frost October 14 (5 days later). Frost-free season 167 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 UW Arboretum - Madison: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 17, 20% May 11, 30% May 7, 40% May 4, 50% May 1, 60% April 29, 70% April 25, 80% April 22, 90% April 18. Observed last spring frost in recent years: 2021 May 11, 2022 April 28, 2023 April 26, 2024 April 25, 2025 May 9, 2026 May 10.Spring: last frostChance of a frost after this date10%50%90%May 1May 17May 1Apr 182021: May 112022: April 282023: April 262024: April 252025: May 92026: May 10Fall at UW Arboretum - Madison: chance of a frost before this dateFall, chance of a frost before the date: 10% September 26, 20% October 1, 30% October 3, 40% October 6, 50% October 9, 60% October 12, 70% October 15, 80% October 18, 90% October 24. Observed first fall frost in recent years: 2021 October 23, 2022 October 8, 2023 October 11, 2024 October 16, 2025 October 9.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 26Oct 9Oct 242021: October 232022: October 82023: October 112024: October 162025: October 9
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 28October 8
2023April 26October 11
2024April 25October 16
2025May 9October 9
2026May 10season not over yet

What these dates mean

The two 32 °F 50 % dates—May 1 and October 9—are 161 days apart, framing the period in which gardeners at UW Arboretum – Madison can expect an even chance of a light frost either side. These median dates are not frost dates themselves; they simply mark the point where the probability of a frost later (spring) or earlier (fall) is 50 %. The hard-frost 50 % dates are April 20 in spring and October 20 in fall.

For a low-risk schedule, the cautious spring date is May 17, when only a 10 % chance of a light frost remains, making it the preferred day to set out tender crops. In autumn, the cautious date is September 26, with only a 10 % chance that a light frost has arrived, so it is the recommended time to finish harvesting tender crops. A hard frost at 28 °F can damage plant tissue more severely than a light frost at 32 °F.

How to read the probabilities

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

  • Spring: "10% after May 17" 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 26" 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 UW Arboretum - Madison, WINumbered nearest stations: 1 — Charmany Farm, WI — 3 mi; 2 — Madison (Madison-Dane Airport), WI — 8 mi; 3 — Arlington, WI — 19 mi; 4 — Brodhead, WI — 29 mi; 5 — Fort Atkinson, WI — 30 mi.ILIA25 mi · 40 km1. Charmany Farm, WI — 3 mi12. Madison (Madison-Dane Airport), WI — 8 mi23. Arlington, WI — 19 mi34. Brodhead, WI — 29 mi45. Fort Atkinson, WI — 30 mi5
  1. Charmany Farm, WI 3 mi (5 km)
  2. Madison (Madison-Dane Airport), WI 8 mi (13 km)
  3. Arlington, WI 19 mi (30 km)
  4. Brodhead, WI 29 mi (47 km)
  5. Fort Atkinson, WI 30 mi (49 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: 43.0411, -89.4286.