U.S. Frost Dates by Weather Station

NOAA station USC00475474 · Wisconsin

Frost Dates near Wauwatosa, WI

NOAA weather station Mount Mary College (USC00475474), Wisconsin · elevation 715 ft (218 m) · hardiness zone 5b*

Wauwatosa is the nearest town to the station (1.9 mi away) in GeoNames (CC BY 4.0). The dates below are measured at the station, not in the town itself.

  • Lower-risk planting dateafter May 12only 1 spring in 10 still has a frost later
  • Typical last frostApril 2650% chance of a frost after it
  • Typical first fall frostOctober 1850% chance of a frost before it
  • Frost-free season173 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season near Wauwatosa, WISpring: a frost after April 12 in 9 years out of 10, after April 26 in half of the years, after May 12 in 1 year out of 10. Fall: the first frost comes before October 2 in 1 year out of 10, before October 18 in half of the years, before November 1 in 9 years out of 10. Typical frost-free season: 173 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 26First frost ~Oct 18Frost season near Wauwatosa, WISpring: a frost after April 12 in 9 years out of 10, after April 26 in half of the years, after May 12 in 1 year out of 10. Fall: the first frost comes before October 2 in 1 year out of 10, before October 18 in half of the years, before November 1 in 9 years out of 10. Typical frost-free season: 173 days.JFMAMJJASONDLast frost ~Apr 26First frost ~Oct 18
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 12October 2
50% (typical)April 26October 18
90% (likely)April 12November 1
Frost-free season (32°F, 50% chance)
173 days
Hard frost (28°F), last in spring, 50% chance after
April 14
Hard frost (28°F), first in fall, 50% chance before
October 30

The last 15 years (2006–2020 normals)

Typical last frost April 27 (1 day later than the 30-year normal), typical first fall frost October 20 (2 days later). Frost-free season 176 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 near Wauwatosa: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 12, 20% May 6, 30% May 2, 40% April 29, 50% April 26, 60% April 23, 70% April 20, 80% April 16, 90% April 12.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 12Apr 26Apr 12Fall near Wauwatosa: chance of a frost before this dateFall, chance of a frost before the date: 10% October 2, 20% October 7, 30% October 12, 40% October 15, 50% October 18, 60% October 22, 70% October 24, 80% October 27, 90% November 1.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Oct 2Oct 18Nov 1
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

Planting tender crops on the early spring date of April 12 carries a 90 % chance of a frost and is a gamble for gardeners in the Wauwatosa area. The cautious date for setting out tender crops is May 12, when only a 10 % chance of frost remains.

The 50% date for light frost in spring is April 26, and the fall 50% date is October 18; at each of these dates the probability of frost is exactly fifty percent. The 50% hard-frost dates are April 14 and October 30, and a hard frost at 28 °F can injure plants more severely than a light frost at 32 °F.

For a cautious fall plan, the date to finish harvesting tender crops is October 2, which carries only a 10 % chance of an earlier frost; counting on crops as late as November 1 would be a gamble with a 90 % chance of frost.

How to read the probabilities

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

  • Spring: "10% after May 12" 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 October 2" 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 Wauwatosa, WINumbered nearest stations: 1 — near Milwaukee, WI — 10 mi; 2 — Germantown, WI — 12 mi; 3 — Oconomowoc, WI — 24 mi; 4 — Hartford, WI — 26 mi; 5 — Racine, WI — 28 mi.WI25 mi · 40 km1. near Milwaukee, WI — 10 mi12. Germantown, WI — 12 mi23. Oconomowoc, WI — 24 mi34. Hartford, WI — 26 mi45. Racine, WI — 28 mi5
  1. near Milwaukee, WI 10 mi (17 km)
  2. Germantown, WI 12 mi (20 km)
  3. Oconomowoc, WI 24 mi (39 km)
  4. Hartford, WI 26 mi (42 km)
  5. Racine, WI 28 mi (46 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: 43.0722, -88.0294.