U.S. Frost Dates by Weather Station

NOAA station USC00478919 · Wisconsin

Frost Dates for Watertown, WI

NOAA weather station Watertown WWTP (USC00478919), Wisconsin · elevation 825 ft (252 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 13only 1 spring in 10 still has a frost later
  • Typical last frostApril 2850% chance of a frost after it
  • Typical first fall frostOctober 1250% chance of a frost before it
  • Frost-free season167 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Watertown, WISpring: a frost after April 14 in 9 years out of 10, after April 28 in half of the years, after May 13 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 27 in 9 years out of 10. Typical frost-free season: 167 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 28First frost ~Oct 12Frost season at Watertown, WISpring: a frost after April 14 in 9 years out of 10, after April 28 in half of the years, after May 13 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 27 in 9 years out of 10. Typical frost-free season: 167 days.JFMAMJJASONDLast frost ~Apr 28First 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 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 13September 28
50% (typical)April 28October 12
90% (likely)April 14October 27
Frost-free season (32°F, 50% chance)
167 days
Hard frost (28°F), last in spring, 50% chance after
April 16
Hard frost (28°F), first in fall, 50% chance before
October 25

The last 15 years (2006–2020 normals)

Typical last frost April 29 (1 day later than the 30-year normal), typical first fall frost October 16 (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 Watertown: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 13, 20% May 7, 30% May 3, 40% April 30, 50% April 28, 60% April 25, 70% April 22, 80% April 18, 90% April 14. Observed last spring frost in recent years: 2021 May 11, 2022 April 28, 2023 April 27, 2024 April 26, 2025 April 16, 2026 May 7.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 13Apr 28Apr 142021: May 112022: April 282023: April 272024: April 262025: April 162026: May 7Fall at Watertown: chance of a frost before this dateFall, chance of a frost before the date: 10% September 28, 20% October 3, 30% October 6, 40% October 10, 50% October 12, 60% October 16, 70% October 18, 80% October 22, 90% October 27. Observed first fall frost in recent years: 2021 October 22, 2022 October 8, 2023 October 17, 2024 October 16, 2025 October 24.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 28Oct 12Oct 272021: October 222022: October 82023: October 172024: 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 11October 22
2022April 28October 8
2023April 27October 17
2024April 26October 16
2025April 16October 24
2026May 7season not over yet

What these dates mean

May 13 is the cautious spring date for Watertown, Wisconsin; with only a 10 % chance of a light frost occurring later, a gardener can plan to set out tender crops after that day. The 50% spring date, April 28, marks the point at which a light frost is equally likely to happen later, while the 50% fall date, October 12, marks the point at which a light frost is equally likely to have arrived earlier. September 28 is the cautious fall date, carrying a 10 % chance that a light frost has already arrived, and therefore guides the latest time to finish harvesting tender crops. A hard frost at 28 °F, represented by the median dates April 16 and October 25, can injure plants that would survive a 32 °F light frost, making it a more serious risk.

How to read the probabilities

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

  • Spring: "10% after May 13" 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 Watertown, WINumbered nearest stations: 1 — Oconomowoc, WI — 13 mi; 2 — Horicon, WI — 19 mi; 3 — Beaver Dam, WI — 19 mi; 4 — Fort Atkinson, WI — 20 mi; 5 — Hartford, WI — 20 mi.WI25 mi · 40 km1. Oconomowoc, WI — 13 mi12. Horicon, WI — 19 mi23. Beaver Dam, WI — 19 mi34. Fort Atkinson, WI — 20 mi45. Hartford, WI — 20 mi5
  1. Oconomowoc, WI 13 mi (21 km)
  2. Horicon, WI 19 mi (31 km)
  3. Beaver Dam, WI 19 mi (31 km)
  4. Fort Atkinson, WI 20 mi (32 km)
  5. Hartford, WI 20 mi (32 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: 43.1742, -88.7364.