U.S. Frost Dates by Weather Station

NOAA station USC00479190 · Wisconsin

Frost Dates for Whitewater, WI

NOAA weather station Whitewater (USC00479190), Wisconsin · elevation 875 ft (267 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 20only 1 spring in 10 still has a frost later
  • Typical last frostMay 250% chance of a frost after it
  • Typical first fall frostOctober 950% chance of a frost before it
  • Frost-free season157 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Whitewater, WISpring: a frost after April 18 in 9 years out of 10, after May 2 in half of the years, after May 20 in 1 year out of 10. Fall: the first frost comes before September 25 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: 157 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 2First frost ~Oct 9Frost season at Whitewater, WISpring: a frost after April 18 in 9 years out of 10, after May 2 in half of the years, after May 20 in 1 year out of 10. Fall: the first frost comes before September 25 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: 157 days.JFMAMJJASONDLast frost ~May 2First 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.Today

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 20September 25
50% (typical)May 2October 9
90% (likely)April 18October 24
Frost-free season (32°F, 50% chance)
157 days
Hard frost (28°F), last in spring, 50% chance after
April 20
Hard frost (28°F), first in fall, 50% chance before
October 22

The last 15 years (2006–2020 normals)

Typical last frost May 1 (1 day earlier than the 30-year normal), typical first fall frost October 13 (4 days later). Frost-free season 162 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 Whitewater: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 20, 20% May 15, 30% May 10, 40% May 6, 50% May 2, 60% April 30, 70% April 27, 80% April 23, 90% April 18. Observed last spring frost in recent years: 2021 May 13, 2022 April 28, 2023 April 27, 2024 April 26, 2025 May 9, 2026 May 10.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 20May 2Apr 182021: May 132022: April 282023: April 272024: April 262025: May 92026: May 10Fall at Whitewater: chance of a frost before this dateFall, chance of a frost before the date: 10% September 25, 20% September 30, 30% October 3, 40% October 6, 50% October 9, 60% October 13, 70% October 15, 80% October 19, 90% October 24. Observed first fall frost in recent years: 2021 October 22, 2022 September 29, 2023 October 12, 2024 October 16, 2025 October 24.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 25Oct 9Oct 242021: October 222022: September 292023: October 122024: 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 28September 29
2023April 27October 12
2024April 26October 16
2025May 9October 24
2026May 10season not over yet

What these dates mean

May 20 is the cautious spring date for Whitewater, Wisconsin; with only a 10 % chance of a light frost occurring later, it lets a gardener set out tender crops. The counterpart cautious fall date is September 25, when there is just a 10 % chance that a light frost has already arrived, giving a gardener a clear point to finish harvesting tender crops. The dates reflect a 30-year record of observations.

The 50 % light-frost dates are May 2 in spring and October 9 in fall; each marks an even odds of a light frost occurring after or before the date, respectively. Hard-frost risk is tracked separately, with the 50 % hard-frost dates of April 20 and October 22, because temperatures of 28 °F can cause more severe damage than the milder 32 °F light frosts.

How to read the probabilities

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

  • Spring: "10% after May 20" 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 25" 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 Whitewater, WINumbered nearest stations: 1 — Fort Atkinson, WI — 8 mi; 2 — Oconomowoc, WI — 21 mi; 3 — Watertown, WI — 22 mi; 4 — near Janesville, WI — 23 mi; 5 — Burlington, WI — 28 mi.25 mi · 40 km1. Fort Atkinson, WI — 8 mi12. Oconomowoc, WI — 21 mi23. Watertown, WI — 22 mi34. near Janesville, WI — 23 mi45. Burlington, WI — 28 mi5
  1. Fort Atkinson, WI 8 mi (12 km)
  2. Oconomowoc, WI 21 mi (33 km)
  3. Watertown, WI 22 mi (36 km)
  4. near Janesville, WI 23 mi (36 km)
  5. Burlington, WI 28 mi (44 km)

Sources

* Hardiness zone 5b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 42.8508, -88.7247.