U.S. Frost Dates by Weather Station

NOAA station USC00470904 · Wisconsin

Frost Dates for Bloomer, WI

NOAA weather station Bloomer (USC00470904), Wisconsin · elevation 990 ft (302 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 19only 1 spring in 10 still has a frost later
  • Typical last frostMay 550% chance of a frost after it
  • Typical first fall frostOctober 350% chance of a frost before it
  • Frost-free season151 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Bloomer, WISpring: a frost after April 23 in 9 years out of 10, after May 5 in half of the years, after May 19 in 1 year out of 10. Fall: the first frost comes before September 20 in 1 year out of 10, before October 3 in half of the years, before October 17 in 9 years out of 10. Typical frost-free season: 151 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 5First frost ~Oct 3Frost season at Bloomer, WISpring: a frost after April 23 in 9 years out of 10, after May 5 in half of the years, after May 19 in 1 year out of 10. Fall: the first frost comes before September 20 in 1 year out of 10, before October 3 in half of the years, before October 17 in 9 years out of 10. Typical frost-free season: 151 days.JFMAMJJASONDLast frost ~May 5First frost ~Oct 3
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 19September 20
50% (typical)May 5October 3
90% (likely)April 23October 17
Frost-free season (32°F, 50% chance)
151 days
Hard frost (28°F), last in spring, 50% chance after
April 26
Hard frost (28°F), first in fall, 50% chance before
October 15

The last 15 years (2006–2020 normals)

Typical last frost May 5 (same as the 30-year normal), typical first fall frost October 7 (4 days later). Frost-free season 152 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 Bloomer: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 19, 20% May 14, 30% May 11, 40% May 8, 50% May 5, 60% May 3, 70% May 1, 80% April 28, 90% April 23. Observed last spring frost in recent years: 2021 May 12, 2022 May 4, 2023 May 3, 2024 April 25, 2025 May 3, 2026 May 11.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 19May 5Apr 232021: May 122022: May 42023: May 32024: April 252025: May 32026: May 11Fall at Bloomer: chance of a frost before this dateFall, chance of a frost before the date: 10% September 20, 20% September 26, 30% September 28, 40% October 1, 50% October 3, 60% October 6, 70% October 9, 80% October 12, 90% October 17. Observed first fall frost in recent years: 2021 October 22, 2022 September 28, 2023 October 17, 2024 October 7, 2025 October 8.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 20Oct 3Oct 172021: October 222022: September 282023: October 172024: October 72025: October 8
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 12October 22
2022May 4September 28
2023May 3October 17
2024April 25October 7
2025May 3October 8
2026May 11season not over yet

What these dates mean

The 151 days between the 50% light-frost dates of May 5 and October 3 in Bloomer frame the main growing season, allowing tender crops to be planted, matured, and harvested within that span. For a gardener, the 50% dates are simply the points where the chance of a light frost is even; they do not mark a frost occurrence themselves.

In spring the cautious date for setting out tender crops is May 19, when there is only a 10% chance of a frost later, while April 23 carries a 90% chance and is a gamble. In fall the cautious date to finish harvesting tender crops is September 20, with a 10% chance of a frost earlier, whereas October 17 has a 90% chance and is a gamble. The median hard-frost dates are April 26 in spring and October 15 in fall.

A hard frost at 28°F can injure or kill plants that survive a light frost at 32°F, making the lower temperature a greater 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 19" 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 20" 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 Bloomer, WINumbered nearest stations: 1 — Eau Claire, WI — 16 mi; 2 — Ridgeland, WI — 21 mi; 3 — Rice Lake, WI — 26 mi; 4 — Menomonie, WI — 27 mi; 5 — Mondovi, WI — 37 mi.MN25 mi · 40 km1. Eau Claire, WI — 16 mi12. Ridgeland, WI — 21 mi23. Rice Lake, WI — 26 mi34. Menomonie, WI — 27 mi45. Mondovi, WI — 37 mi5
  1. Eau Claire, WI 16 mi (25 km)
  2. Ridgeland, WI 21 mi (34 km)
  3. Rice Lake, WI 26 mi (43 km)
  4. Menomonie, WI 27 mi (43 km)
  5. Mondovi, WI 37 mi (60 km)

Sources

* Hardiness zone 4b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 45.0908, -91.4864.