U.S. Frost Dates by Weather Station

NOAA station USW00094846 · Illinois

Frost Dates for Chicago (O'Hare Airport), IL

NOAA weather station Chicago O'Hare International Airport (USW00094846), Illinois · elevation 658 ft (201 m) · hardiness zone 6a*

  • Lower-risk planting dateafter May 1only 1 spring in 10 still has a frost later
  • Typical last frostApril 1650% chance of a frost after it
  • Typical first fall frostOctober 2850% chance of a frost before it
  • Frost-free season193 daystypical year, 32°F
  • Hardiness zone6acalculated*

The year at a glance

Frost season at Chicago (O'Hare Airport), ILSpring: a frost after April 3 in 9 years out of 10, after April 16 in half of the years, after May 1 in 1 year out of 10. Fall: the first frost comes before October 15 in 1 year out of 10, before October 28 in half of the years, before November 11 in 9 years out of 10. Typical frost-free season: 193 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 16First frost ~Oct 28Frost season at Chicago (O'Hare Airport), ILSpring: a frost after April 3 in 9 years out of 10, after April 16 in half of the years, after May 1 in 1 year out of 10. Fall: the first frost comes before October 15 in 1 year out of 10, before October 28 in half of the years, before November 11 in 9 years out of 10. Typical frost-free season: 193 days.JFMAMJJASONDLast frost ~Apr 16First frost ~Oct 28
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.Today

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 1October 15
50% (typical)April 16October 28
90% (likely)April 3November 11
Frost-free season (32°F, 50% chance)
193 days
Hard frost (28°F), last in spring, 50% chance after
April 5
Hard frost (28°F), first in fall, 50% chance before
November 7

The last 15 years (2006–2020 normals)

Typical last frost April 15 (1 day earlier than the 30-year normal), typical first fall frost October 31 (3 days later). Frost-free season 196 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 Chicago (O'Hare Airport): chance of a frost after this dateSpring, chance of a frost after the date: 10% May 1, 20% April 26, 30% April 22, 40% April 19, 50% April 16, 60% April 14, 70% April 11, 80% April 8, 90% April 3. Observed last spring frost in recent years: 2021 April 22, 2022 April 17, 2023 April 26, 2024 April 6, 2025 April 8, 2026 May 2.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 1Apr 16Apr 32021: April 222022: April 172023: April 262024: April 62025: April 82026: May 2Fall at Chicago (O'Hare Airport): chance of a frost before this dateFall, chance of a frost before the date: 10% October 15, 20% October 20, 30% October 24, 40% October 26, 50% October 28, 60% October 31, 70% November 3, 80% November 5, 90% November 11. Observed first fall frost in recent years: 2021 November 2, 2022 November 11, 2023 October 30, 2024 November 20, 2025 November 9.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Oct 15Oct 28Nov 112021: November 22022: November 112023: October 302024: November 202025: November 9
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
2021April 22November 2
2022April 17November 11
2023April 26October 30
2024April 6November 20
2025April 8November 9
2026May 2season not over yet

What these dates mean

Setting out tender crops on April 3 in Chicago (O’Hare Airport) carries a 90 % chance of a frost later than this date, so it is a gamble for growers. The cautious spring date for tender crops is May 1, when only a 10 % chance of a frost later than that day remains.

The 50% date in spring is April 16, which means there is a 50 % chance of a frost later than this date; in fall the 50% date is October 28, indicating a 50 % chance of a frost earlier than this date. The cautious fall date for finishing tender crops is October 15, when the probability of a frost earlier than that day is just 10 %.

A hard frost, recorded at 28 °F, is more consequential than a light frost at 32 °F because it can damage plant tissue that survives the milder temperature. The 50 % hard-frost dates are April 5 and November 7.

How to read the probabilities

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

  • Spring: "10% after May 1" 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 15" 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 Chicago (O'Hare Airport), ILNumbered nearest stations: 1 — Chicago Botanic Garden, IL — 13 mi; 2 — Elgin, IL — 19 mi; 3 — near Chicago, IL — 20 mi; 4 — Aurora, IL — 24 mi; 5 — near McHenry, IL — 27 mi.ILWIINMI25 mi · 40 km1. Chicago Botanic Garden, IL — 13 mi12. Elgin, IL — 19 mi23. near Chicago, IL — 20 mi34. Aurora, IL — 24 mi45. near McHenry, IL — 27 mi5
  1. Chicago Botanic Garden, IL 13 mi (20 km)
  2. Elgin, IL 19 mi (30 km)
  3. near Chicago, IL 20 mi (31 km)
  4. Aurora, IL 24 mi (39 km)
  5. near McHenry, IL 27 mi (44 km)

Sources

* Hardiness zone 6a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 41.995, -87.9336.