U.S. Frost Dates by Weather Station

NOAA station USC00110338 · Illinois

Frost Dates for Aurora, IL

NOAA weather station Aurora (USC00110338), Illinois · elevation 660 ft (201 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 4only 1 spring in 10 still has a frost later
  • Typical last frostApril 1950% chance of a frost after it
  • Typical first fall frostOctober 2350% chance of a frost before it
  • Frost-free season185 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Aurora, ILSpring: a frost after April 5 in 9 years out of 10, after April 19 in half of the years, after May 4 in 1 year out of 10. Fall: the first frost comes before October 9 in 1 year out of 10, before October 23 in half of the years, before November 3 in 9 years out of 10. Typical frost-free season: 185 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 19First frost ~Oct 23Frost season at Aurora, ILSpring: a frost after April 5 in 9 years out of 10, after April 19 in half of the years, after May 4 in 1 year out of 10. Fall: the first frost comes before October 9 in 1 year out of 10, before October 23 in half of the years, before November 3 in 9 years out of 10. Typical frost-free season: 185 days.JFMAMJJASONDLast frost ~Apr 19First frost ~Oct 23
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 4October 9
50% (typical)April 19October 23
90% (likely)April 5November 3
Frost-free season (32°F, 50% chance)
185 days
Hard frost (28°F), last in spring, 50% chance after
April 8
Hard frost (28°F), first in fall, 50% chance before
November 2

The last 15 years (2006–2020 normals)

Typical last frost April 20 (1 day later than the 30-year normal), typical first fall frost October 24 (1 day later). Frost-free season 188 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 Aurora: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 4, 20% April 29, 30% April 25, 40% April 22, 50% April 19, 60% April 16, 70% April 13, 80% April 10, 90% April 5. Observed last spring frost in recent years: 2021 April 22, 2022 April 18, 2023 April 28, 2024 April 22, 2025 April 9, 2026 May 2.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 4Apr 19Apr 52021: April 222022: April 182023: April 282024: April 222025: April 92026: May 2Fall at Aurora: chance of a frost before this dateFall, chance of a frost before the date: 10% October 9, 20% October 15, 30% October 18, 40% October 21, 50% October 23, 60% October 25, 70% October 28, 80% October 30, 90% November 3. Observed first fall frost in recent years: 2021 November 1, 2022 October 15, 2023 October 30, 2024 November 21, 2025 October 24.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Oct 9Oct 23Nov 32021: November 12022: October 152023: October 302024: November 212025: October 24
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 1
2022April 18October 15
2023April 28October 30
2024April 22November 21
2025April 9October 24
2026May 2season not over yet

What these dates mean

Setting out tender crops on April 5 in Aurora is a gamble, because there is a 90 % chance that a light frost will occur later in the season. The cautious spring date for planting tender crops is May 4, when only a 10 % chance of a light frost remains.

The 50 % date of April 19 marks the moment when a light frost is equally likely to happen before or after, giving gardeners a statistical midpoint for spring risk. In the fall, October 23 serves the same purpose for light-frost timing, while the cautious date to finish harvesting tender crops is October 9, with just a 10 % chance that frost has already arrived. A hard frost at 28 °F can injure plants that tolerate a 32 °F light frost, so the 50 % hard-frost dates of April 8 and November 2 signal when that greater danger becomes equally probable.

How to read the probabilities

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

  • Spring: "10% after May 4" 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 9" 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 Aurora, ILNumbered nearest stations: 1 — Elgin, IL — 20 mi; 2 — near Joliet, IL — 22 mi; 3 — Chicago (O'Hare Airport), IL — 24 mi; 4 — De Kalb, IL — 26 mi; 5 — near Chicago, IL — 28 mi.ILIN25 mi · 40 km1. Elgin, IL — 20 mi12. near Joliet, IL — 22 mi23. Chicago (O'Hare Airport), IL — 24 mi34. De Kalb, IL — 26 mi45. near Chicago, IL — 28 mi5
  1. Elgin, IL 20 mi (31 km)
  2. near Joliet, IL 22 mi (35 km)
  3. Chicago (O'Hare Airport), IL 24 mi (39 km)
  4. De Kalb, IL 26 mi (42 km)
  5. near Chicago, IL 28 mi (44 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: 41.7803, -88.3092.