U.S. Frost Dates by Weather Station

NOAA station USC00478827 · Wisconsin

Frost Dates for Viroqua, WI

NOAA weather station Viroqua (USC00478827), Wisconsin · elevation 1255 ft (383 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 21only 1 spring in 10 still has a frost later
  • Typical last frostMay 750% chance of a frost after it
  • Typical first fall frostOctober 250% chance of a frost before it
  • Frost-free season148 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Viroqua, WISpring: a frost after April 23 in 9 years out of 10, after May 7 in half of the years, after May 21 in 1 year out of 10. Fall: the first frost comes before September 18 in 1 year out of 10, before October 2 in half of the years, before October 17 in 9 years out of 10. Typical frost-free season: 148 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 7First frost ~Oct 2Frost season at Viroqua, WISpring: a frost after April 23 in 9 years out of 10, after May 7 in half of the years, after May 21 in 1 year out of 10. Fall: the first frost comes before September 18 in 1 year out of 10, before October 2 in half of the years, before October 17 in 9 years out of 10. Typical frost-free season: 148 days.JFMAMJJASONDLast frost ~May 7First frost ~Oct 2
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 21September 18
50% (typical)May 7October 2
90% (likely)April 23October 17
Frost-free season (32°F, 50% chance)
148 days
Hard frost (28°F), last in spring, 50% chance after
April 27
Hard frost (28°F), first in fall, 50% chance before
October 13

The last 15 years (2006–2020 normals)

Typical last frost May 2 (5 days earlier than the 30-year normal), typical first fall frost October 11 (9 days later). Frost-free season 161 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 Viroqua: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 21, 20% May 17, 30% May 13, 40% May 10, 50% May 7, 60% May 4, 70% May 1, 80% April 28, 90% April 23. Observed last spring frost in recent years: 2021 May 11, 2022 April 28, 2023 May 3, 2024 April 25, 2025 April 17, 2026 May 7.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 21May 7Apr 232021: May 112022: April 282023: May 32024: April 252025: April 172026: May 7Fall at Viroqua: chance of a frost before this dateFall, chance of a frost before the date: 10% September 18, 20% September 23, 30% September 27, 40% September 30, 50% October 2, 60% October 5, 70% October 8, 80% October 11, 90% October 17. Observed first fall frost in recent years: 2021 October 22, 2022 September 28, 2023 October 11, 2024 October 15, 2025 October 23.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 18Oct 2Oct 172021: October 222022: September 282023: October 112024: October 152025: 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 22
2022April 28September 28
2023May 3October 11
2024April 25October 15
2025April 17October 23
2026May 7season not over yet

What these dates mean

May 21 is the cautious spring date, with only a 10% chance of a frost later than this date, so a gardener can plan to set out tender crops. The 50% date is May 7, which represents a 50% chance of a frost later than that day, while the 50% hard-frost date is April 27. The early spring gamble, April 23, carries a 90% chance of frost later.

In fall, September 18 serves as the cautious date, with a 10% chance of a frost earlier than this day, guiding the final harvest of tender crops. The 50% date is October 2, giving a 50% chance of a frost earlier than that date, and the 50% hard-frost date is October 13. A hard frost at 28°F can kill plant tissue that would survive a light frost at 32°F.

How to read the probabilities

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

  • Spring: "10% after May 21" 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 18" 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 Viroqua, WINumbered nearest stations: 1 — Gays Mills, WI — 17 mi; 2 — Genoa Dam 8, WI — 18 mi; 3 — Sparta, WI — 26 mi; 4 — Lynxville Dam 9, WI — 26 mi; 5 — La Crosse, WI — 29 mi.WIIAMN25 mi · 40 km1. Gays Mills, WI — 17 mi12. Genoa Dam 8, WI — 18 mi23. Sparta, WI — 26 mi34. Lynxville Dam 9, WI — 26 mi45. La Crosse, WI — 29 mi5
  1. Gays Mills, WI 17 mi (27 km)
  2. Genoa Dam 8, WI 18 mi (28 km)
  3. Sparta, WI 26 mi (42 km)
  4. Lynxville Dam 9, WI 26 mi (43 km)
  5. La Crosse, 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: 43.5594, -90.8761.