U.S. Frost Dates by Weather Station

NOAA station USC00470696 · Wisconsin

Frost Dates for Beloit, WI

NOAA weather station Beloit (USC00470696), Wisconsin · elevation 788 ft (240 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 16only 1 spring in 10 still has a frost later
  • Typical last frostMay 150% chance of a frost after it
  • Typical first fall frostOctober 1250% chance of a frost before it
  • Frost-free season162 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Beloit, WISpring: a frost after April 17 in 9 years out of 10, after May 1 in half of the years, after May 16 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 24 in 9 years out of 10. Typical frost-free season: 162 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 1First frost ~Oct 12Frost season at Beloit, WISpring: a frost after April 17 in 9 years out of 10, after May 1 in half of the years, after May 16 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 24 in 9 years out of 10. Typical frost-free season: 162 days.JFMAMJJASONDLast frost ~May 1First 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 27 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 16September 28
50% (typical)May 1October 12
90% (likely)April 17October 24
Frost-free season (32°F, 50% chance)
162 days
Hard frost (28°F), last in spring, 50% chance after
April 20
Hard frost (28°F), first in fall, 50% chance before
October 23

The last 15 years (2006–2020 normals)

Typical last frost May 1 (same as the 30-year normal), typical first fall frost October 16 (4 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 Beloit: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 16, 20% May 11, 30% May 7, 40% May 4, 50% May 1, 60% April 29, 70% April 26, 80% April 22, 90% April 17. Observed last spring frost in recent years: 2021 April 23, 2022 April 28, 2023 April 27, 2024 April 25, 2025 April 9, 2026 May 8.Spring: last frostChance of a frost after this date10%50%90%May 1May 16May 1Apr 172021: April 232022: April 282023: April 272024: April 252025: April 92026: May 8Fall at Beloit: chance of a frost before this dateFall, chance of a frost before the date: 10% September 28, 20% October 2, 30% October 6, 40% October 9, 50% October 12, 60% October 15, 70% October 18, 80% October 21, 90% October 24. Observed first fall frost in recent years: 2021 November 1, 2022 October 8, 2023 October 30, 2024 October 16, 2025 October 24.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 28Oct 12Oct 242021: November 12022: October 82023: October 302024: 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
2021April 23November 1
2022April 28October 8
2023April 27October 30
2024April 25October 16
2025April 9October 24
2026May 8season not over yet

What these dates mean

The cautious fall date in Beloit for finishing the harvest is September 28, when there is only a 10% chance that a light frost has already arrived. By that time tender crops should be harvested, since a later date such as October 24 carries a 90% chance of a frost and would be a gamble.

The 50% light-frost dates are May 1 in spring and October 12 in fall; each marks the point at which a light frost is equally likely to occur on either side of the date. The 50% hard-frost dates are April 20 and October 23, and hard frost can damage plants that survive a light frost, making it a more critical threshold.

The cautious spring date for setting out tender crops is May 16, which has a 10% chance of a frost later than that date, while planting on April 17 would be a gamble with a 90% chance of frost.

How to read the probabilities

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

  • Spring: "10% after May 16" 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 Beloit, WINumbered nearest stations: 1 — near Janesville, WI — 9 mi; 2 — Brodhead, WI — 20 mi; 3 — Rockford, IL — 22 mi; 4 — Whitewater, WI — 29 mi; 5 — Fort Atkinson, WI — 29 mi.WIIA25 mi · 40 km1. near Janesville, WI — 9 mi12. Brodhead, WI — 20 mi23. Rockford, IL — 22 mi34. Whitewater, WI — 29 mi45. Fort Atkinson, WI — 29 mi5
  1. near Janesville, WI 9 mi (15 km)
  2. Brodhead, WI 20 mi (32 km)
  3. Rockford, IL 22 mi (35 km)
  4. Whitewater, WI 29 mi (46 km)
  5. Fort Atkinson, WI 29 mi (47 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: 42.5039, -89.0311.