U.S. Frost Dates by Weather Station

NOAA station USC00474546 · Wisconsin

Frost Dates for Lancaster, WI

NOAA weather station Lancaster 4 WSW (USC00474546), Wisconsin · elevation 1040 ft (317 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 11only 1 spring in 10 still has a frost later
  • Typical last frostApril 2750% chance of a frost after it
  • Typical first fall frostOctober 1150% chance of a frost before it
  • Frost-free season166 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Lancaster, WISpring: a frost after April 11 in 9 years out of 10, after April 27 in half of the years, after May 11 in 1 year out of 10. Fall: the first frost comes before September 27 in 1 year out of 10, before October 11 in half of the years, before October 24 in 9 years out of 10. Typical frost-free season: 166 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 27First frost ~Oct 11Frost season at Lancaster, WISpring: a frost after April 11 in 9 years out of 10, after April 27 in half of the years, after May 11 in 1 year out of 10. Fall: the first frost comes before September 27 in 1 year out of 10, before October 11 in half of the years, before October 24 in 9 years out of 10. Typical frost-free season: 166 days.JFMAMJJASONDLast frost ~Apr 27First frost ~Oct 11
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 28 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 11September 27
50% (typical)April 27October 11
90% (likely)April 11October 24
Frost-free season (32°F, 50% chance)
166 days
Hard frost (28°F), last in spring, 50% chance after
April 16
Hard frost (28°F), first in fall, 50% chance before
October 22

The last 15 years (2006–2020 normals)

Typical last frost April 29 (2 days later than the 30-year normal), typical first fall frost October 15 (4 days later). Frost-free season 170 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 Lancaster: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 11, 20% May 6, 30% May 3, 40% April 30, 50% April 27, 60% April 24, 70% April 21, 80% April 16, 90% April 11. Observed last spring frost in recent years: 2021 May 11, 2022 April 28, 2023 April 26, 2024 April 24, 2025 April 16, 2026 May 7.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 11Apr 27Apr 112021: May 112022: April 282023: April 262024: April 242025: April 162026: May 7Fall at Lancaster: chance of a frost before this dateFall, chance of a frost before the date: 10% September 27, 20% October 1, 30% October 5, 40% October 8, 50% October 11, 60% October 14, 70% October 17, 80% October 20, 90% October 24. Observed first fall frost in recent years: 2021 October 23, 2022 October 8, 2023 October 11, 2024 October 16, 2025 October 23.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 27Oct 11Oct 242021: October 232022: October 82023: October 112024: October 162025: 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 23
2022April 28October 8
2023April 26October 11
2024April 24October 16
2025April 16October 23
2026May 7season not over yet

What these dates mean

September 27 marks the cautious fall date for finishing the harvest in Lancaster, Wisconsin, when there is only a 10 % chance that a light frost has arrived earlier. In spring the cautious date for setting out tender crops is May 11, carrying a 10 % chance of a frost later, while the early April 11 date represents a 90 % gamble.

For a gardener, the 50 % dates are reference points: April 27 carries a 50 % chance of a light frost later, and October 11 carries a 50 % chance of a light frost earlier. The median hard-frost dates are April 16 and October 22; hard frost at 28 °F can damage plant tissue that survives a light frost at 32 °F. The record spans 28 years, and the interval between the two 32 °F 50 % dates is 166 days.

How to read the probabilities

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

  • Spring: "10% after May 11" 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 27" 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 Lancaster, WINumbered nearest stations: 1 — near Guttenberg, IA — 16 mi; 2 — Dubuque Lock and Dam 11, IA — 21 mi; 3 — Prairie Du Chien, WI — 23 mi; 4 — Dubuque, IA — 30 mi; 5 — Lynxville Dam 9, WI — 31 mi.IAWIILMN25 mi · 40 km1. near Guttenberg, IA — 16 mi12. Dubuque Lock and Dam 11, IA — 21 mi23. Prairie Du Chien, WI — 23 mi34. Dubuque, IA — 30 mi45. Lynxville Dam 9, WI — 31 mi5
  1. near Guttenberg, IA 16 mi (25 km)
  2. Dubuque Lock and Dam 11, IA 21 mi (34 km)
  3. Prairie Du Chien, WI 23 mi (38 km)
  4. Dubuque, IA 30 mi (48 km)
  5. Lynxville Dam 9, 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: 42.8278, -90.7889.