U.S. Frost Dates by Weather Station

NOAA station USC00471416 · Wisconsin

Frost Dates for Charmany Farm, WI

NOAA weather station Charmany Farm (USC00471416), Wisconsin · elevation 1046 ft (319 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 11only 1 spring in 10 still has a frost later
  • Typical last frostApril 2850% chance of a frost after it
  • Typical first fall frostOctober 1550% chance of a frost before it
  • Frost-free season169 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Charmany Farm, WISpring: a frost after April 14 in 9 years out of 10, after April 28 in half of the years, after May 11 in 1 year out of 10. Fall: the first frost comes before September 29 in 1 year out of 10, before October 15 in half of the years, before October 29 in 9 years out of 10. Typical frost-free season: 169 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 28First frost ~Oct 15Frost season at Charmany Farm, WISpring: a frost after April 14 in 9 years out of 10, after April 28 in half of the years, after May 11 in 1 year out of 10. Fall: the first frost comes before September 29 in 1 year out of 10, before October 15 in half of the years, before October 29 in 9 years out of 10. Typical frost-free season: 169 days.JFMAMJJASONDLast frost ~Apr 28First frost ~Oct 15
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 11September 29
50% (typical)April 28October 15
90% (likely)April 14October 29
Frost-free season (32°F, 50% chance)
169 days
Hard frost (28°F), last in spring, 50% chance after
April 17
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 17 (2 days later). Frost-free season 169 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 Charmany Farm: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 11, 20% May 6, 30% May 3, 40% April 30, 50% April 28, 60% April 25, 70% April 22, 80% April 19, 90% April 14.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 11Apr 28Apr 14Fall at Charmany Farm: chance of a frost before this dateFall, chance of a frost before the date: 10% September 29, 20% October 5, 30% October 9, 40% October 12, 50% October 15, 60% October 18, 70% October 21, 80% October 24, 90% October 29.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 29Oct 15Oct 29
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.

What these dates mean

May 11 is the cautious spring date at Charmany Farm, allowing a gardener to plan the setting out of tender crops with only a 10 % chance that a light frost will occur later.

The 50 % spring light-frost date, April 28, marks an even odds point for a frost after that day, while the 50 % fall light-frost date, October 15, marks an even odds point for a frost before that day. For a careful fall schedule, September 29 is the cautious date, giving a 10 % chance that a light frost will have arrived earlier, so it is the date to finish harvesting tender crops. The hard-frost 50 % dates are April 17 in spring and October 25 in fall; a hard frost at 28 °F is more damaging than a light frost at 32 °F because it can freeze plant tissue that would survive a milder chill.

How to read the probabilities

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

  • Spring: "10% after May 11" 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 29" 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 Charmany Farm, WINumbered nearest stations: 1 — UW Arboretum - Madison, WI — 3 mi; 2 — Madison (Madison-Dane Airport), WI — 9 mi; 3 — Arlington, WI — 18 mi; 4 — Brodhead, WI — 31 mi; 5 — Portage, WI — 33 mi.ILIA25 mi · 40 km1. UW Arboretum - Madison, WI — 3 mi12. Madison (Madison-Dane Airport), WI — 9 mi23. Arlington, WI — 18 mi34. Brodhead, WI — 31 mi45. Portage, WI — 33 mi5
  1. UW Arboretum - Madison, WI 3 mi (5 km)
  2. Madison (Madison-Dane Airport), WI 9 mi (14 km)
  3. Arlington, WI 18 mi (29 km)
  4. Brodhead, WI 31 mi (50 km)
  5. Portage, WI 33 mi (52 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: 43.0597, -89.4819.