U.S. Frost Dates by Weather Station

NOAA station USC00475581 · Wisconsin

Frost Dates for Montello, WI

NOAA weather station Montello (USC00475581), Wisconsin · elevation 786 ft (240 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 18only 1 spring in 10 still has a frost later
  • Typical last frostMay 350% chance of a frost after it
  • Typical first fall frostOctober 550% chance of a frost before it
  • Frost-free season153 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Montello, WISpring: a frost after April 21 in 9 years out of 10, after May 3 in half of the years, after May 18 in 1 year out of 10. Fall: the first frost comes before September 22 in 1 year out of 10, before October 5 in half of the years, before October 18 in 9 years out of 10. Typical frost-free season: 153 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 3First frost ~Oct 5Frost season at Montello, WISpring: a frost after April 21 in 9 years out of 10, after May 3 in half of the years, after May 18 in 1 year out of 10. Fall: the first frost comes before September 22 in 1 year out of 10, before October 5 in half of the years, before October 18 in 9 years out of 10. Typical frost-free season: 153 days.JFMAMJJASONDLast frost ~May 3First frost ~Oct 5
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 18September 22
50% (typical)May 3October 5
90% (likely)April 21October 18
Frost-free season (32°F, 50% chance)
153 days
Hard frost (28°F), last in spring, 50% chance after
April 23
Hard frost (28°F), first in fall, 50% chance before
October 16

The last 15 years (2006–2020 normals)

Typical last frost May 4 (1 day later than the 30-year normal), typical first fall frost October 8 (3 days later). Frost-free season 157 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 Montello: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 18, 20% May 13, 30% May 9, 40% May 6, 50% May 3, 60% May 1, 70% April 28, 80% April 25, 90% April 21. Observed last spring frost in recent years: 2021 May 8, 2022 May 5, 2023 May 3, 2024 April 25, 2025 April 17, 2026 May 10.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 18May 3Apr 212021: May 82022: May 52023: May 32024: April 252025: April 172026: May 10Fall at Montello: chance of a frost before this dateFall, chance of a frost before the date: 10% September 22, 20% September 27, 30% September 30, 40% October 3, 50% October 5, 60% October 8, 70% October 11, 80% October 14, 90% October 18. Observed first fall frost in recent years: 2021 October 22, 2022 September 29, 2023 October 22, 2024 October 16, 2025 October 24.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 22Oct 5Oct 182021: October 222022: September 292023: October 222024: 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 8October 22
2022May 5September 29
2023May 3October 22
2024April 25October 16
2025April 17October 24
2026May 10season not over yet

What these dates mean

September 22 marks the cautious fall date in Montello for finishing the harvest of tender crops, with only a 10% chance that a light frost has arrived earlier.

The median 32°F dates are May 3 and October 5; each represents a 50% odds of a light frost occurring later in spring or earlier in fall. The 28°F median dates are April 23 for spring and October 16 for fall, indicating when a hard frost is equally likely to have occurred.

A cautious spring plan uses May 18 as the date to set out tender crops, because only a 10% chance of a light frost remains after that day. A cautious fall plan relies on September 22 to end the tender-crop harvest. Hard frosts matter more than light frosts because the lower temperature can damage plant tissue that survives a 32°F event.

How to read the probabilities

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

  • Spring: "10% after May 18" 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 22" 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 Montello, WINumbered nearest stations: 1 — Portage, WI — 18 mi; 2 — Wisconsin Dells, WI — 25 mi; 3 — Hancock Experiment Farm, WI — 26 mi; 4 — Arlington, WI — 33 mi; 5 — Beaver Dam, WI — 33 mi.25 mi · 40 km1. Portage, WI — 18 mi12. Wisconsin Dells, WI — 25 mi23. Hancock Experiment Farm, WI — 26 mi34. Arlington, WI — 33 mi45. Beaver Dam, WI — 33 mi5
  1. Portage, WI 18 mi (29 km)
  2. Wisconsin Dells, WI 25 mi (41 km)
  3. Hancock Experiment Farm, WI 26 mi (41 km)
  4. Arlington, WI 33 mi (53 km)
  5. Beaver Dam, WI 33 mi (53 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: 43.7806, -89.3169.