U.S. Frost Dates by Weather Station

NOAA station USC00111497 · Illinois

Frost Dates for Chicago Botanic Garden, IL

NOAA weather station Chicago Botanic Garden (USC00111497), Illinois · elevation 630 ft (192 m) · hardiness zone 6a*

  • Lower-risk planting dateafter May 11only 1 spring in 10 still has a frost later
  • Typical last frostApril 2650% chance of a frost after it
  • Typical first fall frostOctober 2150% chance of a frost before it
  • Frost-free season176 daystypical year, 32°F
  • Hardiness zone6acalculated*

The year at a glance

Frost season at Chicago Botanic Garden, ILSpring: a frost after April 11 in 9 years out of 10, after April 26 in half of the years, after May 11 in 1 year out of 10. Fall: the first frost comes before October 5 in 1 year out of 10, before October 21 in half of the years, before November 2 in 9 years out of 10. Typical frost-free season: 176 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 26First frost ~Oct 21Frost season at Chicago Botanic Garden, ILSpring: a frost after April 11 in 9 years out of 10, after April 26 in half of the years, after May 11 in 1 year out of 10. Fall: the first frost comes before October 5 in 1 year out of 10, before October 21 in half of the years, before November 2 in 9 years out of 10. Typical frost-free season: 176 days.JFMAMJJASONDLast frost ~Apr 26First frost ~Oct 21
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 11October 5
50% (typical)April 26October 21
90% (likely)April 11November 2
Frost-free season (32°F, 50% chance)
176 days
Hard frost (28°F), last in spring, 50% chance after
April 13
Hard frost (28°F), first in fall, 50% chance before
November 1

The last 15 years (2006–2020 normals)

Typical last frost April 24 (2 days earlier than the 30-year normal), typical first fall frost October 24 (3 days later). Frost-free season 182 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 Botanic Garden: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 11, 20% May 6, 30% May 2, 40% April 30, 50% April 26, 60% April 23, 70% April 20, 80% April 16, 90% April 11.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 11Apr 26Apr 11Fall at Chicago Botanic Garden: chance of a frost before this dateFall, chance of a frost before the date: 10% October 5, 20% October 11, 30% October 14, 40% October 18, 50% October 21, 60% October 23, 70% October 26, 80% October 30, 90% November 2.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Oct 5Oct 21Nov 2
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 light-frost date at Chicago Botanic Garden; with only a 10 % chance of a frost later, a gardener can plan to set out tender crops after this day.

The median light-frost date, April 26, represents the point at which a frost is equally likely to occur later or not, giving a reference for risk assessment, while the fall median, October 21, marks the same even-odds threshold for frost arriving earlier. October 5 is the cautious fall light-frost date, carrying a 10 % chance that frost has already arrived, so finishing tender-crop harvest by then minimizes risk. Hard frost dates—April 13 in spring and November 1 in fall—are listed because a 28 °F frost can damage plants that survive a 32 °F light frost, making them a more severe threat.

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 October 5" 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 Botanic Garden, ILNumbered nearest stations: 1 — Chicago (O'Hare Airport), IL — 13 mi; 2 — Elgin, IL — 26 mi; 3 — near McHenry, IL — 27 mi; 4 — near Chicago, IL — 28 mi; 5 — Kenosha, WI — 29 mi.ILWIINMI25 mi · 40 km1. Chicago (O'Hare Airport), IL — 13 mi12. Elgin, IL — 26 mi23. near McHenry, IL — 27 mi34. near Chicago, IL — 28 mi45. Kenosha, WI — 29 mi5
  1. Chicago (O'Hare Airport), IL 13 mi (20 km)
  2. Elgin, IL 26 mi (42 km)
  3. near McHenry, IL 27 mi (43 km)
  4. near Chicago, IL 28 mi (45 km)
  5. Kenosha, WI 29 mi (47 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: 42.14, -87.7853.