U.S. Frost Dates by Weather Station

NOAA station USC00470645 · Wisconsin

Frost Dates for Beaver Dam, WI

NOAA weather station Beaver Dam WWTP (USC00470645), Wisconsin · elevation 861 ft (262 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 16only 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 zone5acalculated*

The year at a glance

Frost season at Beaver Dam, WISpring: a frost after April 19 in 9 years out of 10, after May 2 in half of the years, after May 16 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 23 in 9 years out of 10. Typical frost-free season: 157 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 2First frost ~Oct 9Frost season at Beaver Dam, WISpring: a frost after April 19 in 9 years out of 10, after May 2 in half of the years, after May 16 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 23 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.

Frost dates (32°F)

Probability of frost, based on 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 16September 25
50% (typical)May 2October 9
90% (likely)April 19October 23
Frost-free season (32°F, 50% chance)
157 days
Hard frost (28°F), last in spring, 50% chance after
April 22
Hard frost (28°F), first in fall, 50% chance before
October 20

The last 15 years (2006–2020 normals)

Typical last frost May 3 (1 day later than the 30-year normal), typical first fall frost October 11 (2 days later). Frost-free season 159 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 Beaver Dam: 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 2, 60% April 30, 70% April 27, 80% April 23, 90% April 19. Observed last spring frost in recent years: 2021 April 22, 2022 April 28, 2023 April 26, 2024 April 25, 2025 May 21, 2026 May 7.Spring: last frostChance of a frost after this date10%50%90%May 1May 16May 2Apr 192021: April 222022: April 282023: April 262024: April 252025: May 212026: May 7Fall at Beaver Dam: 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 11, 70% October 15, 80% October 18, 90% October 23. Observed first fall frost in recent years: 2021 November 1, 2022 October 15, 2023 October 17, 2024 October 16, 2025 October 12.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 25Oct 9Oct 232021: November 12022: October 152023: October 172024: October 162025: October 12
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 22November 1
2022April 28October 15
2023April 26October 17
2024April 25October 16
2025May 21October 12
2026May 7season not over yet

What these dates mean

The 157 days between the 50% dates of May 2 and October 9 in Beaver Dam mark the span in which a light frost (32 °F) is less than even-odds likely, and within which most tender gardening activities can be scheduled. The median hard-frost dates of April 22 and October 20 indicate when a 28 °F event is equally probable, a colder threshold that can be more damaging.

A cautious spring plan uses the May 16 date, which carries a 10 % chance that a light frost will occur later, while the April 19 date (90 % chance) would be a gamble. In the fall, the September 25 date is the cautious point, offering only a 10 % chance that a light frost has already arrived, whereas October 23 (90 % chance) is risky for late-season tender crops. A hard frost at 28 °F matters more than a light frost at 32 °F because the lower temperature can cause more severe damage to plant tissues.

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 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 Beaver Dam, WINumbered nearest stations: 1 — Horicon, WI — 11 mi; 2 — Watertown, WI — 19 mi; 3 — Hartford, WI — 23 mi; 4 — Arlington, WI — 27 mi; 5 — Oconomowoc, WI — 29 mi.WI25 mi · 40 km1. Horicon, WI — 11 mi12. Watertown, WI — 19 mi23. Hartford, WI — 23 mi34. Arlington, WI — 27 mi45. Oconomowoc, WI — 29 mi5
  1. Horicon, WI 11 mi (17 km)
  2. Watertown, WI 19 mi (31 km)
  3. Hartford, WI 23 mi (37 km)
  4. Arlington, WI 27 mi (43 km)
  5. Oconomowoc, WI 29 mi (47 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: 43.4428, -88.8453.