U.S. Frost Dates by Weather Station

NOAA station USC00110072 · Illinois

Frost Dates for Aledo, IL

NOAA weather station Aledo (USC00110072), Illinois · elevation 730 ft (223 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 6only 1 spring in 10 still has a frost later
  • Typical last frostApril 2250% chance of a frost after it
  • Typical first fall frostOctober 1950% chance of a frost before it
  • Frost-free season181 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Aledo, ILSpring: a frost after April 7 in 9 years out of 10, after April 22 in half of the years, after May 6 in 1 year out of 10. Fall: the first frost comes before October 6 in 1 year out of 10, before October 19 in half of the years, before October 31 in 9 years out of 10. Typical frost-free season: 181 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 22First frost ~Oct 19Frost season at Aledo, ILSpring: a frost after April 7 in 9 years out of 10, after April 22 in half of the years, after May 6 in 1 year out of 10. Fall: the first frost comes before October 6 in 1 year out of 10, before October 19 in half of the years, before October 31 in 9 years out of 10. Typical frost-free season: 181 days.JFMAMJJASONDLast frost ~Apr 22First frost ~Oct 19
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 6October 6
50% (typical)April 22October 19
90% (likely)April 7October 31
Frost-free season (32°F, 50% chance)
181 days
Hard frost (28°F), last in spring, 50% chance after
April 11
Hard frost (28°F), first in fall, 50% chance before
October 29

The last 15 years (2006–2020 normals)

Typical last frost April 22 (same as the 30-year normal), typical first fall frost October 21 (2 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 Aledo: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 6, 20% May 2, 30% April 29, 40% April 25, 50% April 22, 60% April 19, 70% April 16, 80% April 12, 90% April 7. Observed last spring frost in recent years: 2021 April 23, 2022 April 27, 2023 April 27, 2024 April 22, 2025 April 9, 2026 April 21.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 6Apr 22Apr 72021: April 232022: April 272023: April 272024: April 222025: April 92026: April 21Fall at Aledo: chance of a frost before this dateFall, chance of a frost before the date: 10% October 6, 20% October 12, 30% October 14, 40% October 17, 50% October 19, 60% October 21, 70% October 24, 80% October 27, 90% October 31. Observed first fall frost in recent years: 2021 November 1, 2022 October 14, 2023 October 30, 2024 October 16, 2025 October 24.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Oct 6Oct 19Oct 312021: November 12022: October 142023: October 302024: October 162025: 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 23November 1
2022April 27October 14
2023April 27October 30
2024April 22October 16
2025April 9October 24
2026April 21season not over yet

What these dates mean

May 6 carries a 10 % chance of a frost later in the season, making it the cautious spring date for setting out tender crops and giving a gardener the confidence to move seedlings outdoors.

The 50 % light-frost dates are April 22 in spring and October 19 in fall; each represents an even chance that a light frost will occur, serving as a midpoint reference for risk. The 50 % hard-frost dates are April 11 and October 29, indicating when a freeze to 28 °F is as likely as not. In the fall, the cautious date for finishing tender crops is October 6, which has only a 10 % chance that a frost has arrived earlier.

A hard frost at 28 °F can damage plant tissue that a 32 °F light frost typically does not, so it is a more critical 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 6" 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 6" 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 Aledo, ILNumbered nearest stations: 1 — Monmouth, IL — 18 mi; 2 — near Moline, IL — 22 mi; 3 — Muscatine, IA — 22 mi; 4 — near Rock Island, IL — 24 mi; 5 — Galesburg, IL — 26 mi.ILIA25 mi · 40 km1. Monmouth, IL — 18 mi12. near Moline, IL — 22 mi23. Muscatine, IA — 22 mi34. near Rock Island, IL — 24 mi45. Galesburg, IL — 26 mi5
  1. Monmouth, IL 18 mi (30 km)
  2. near Moline, IL 22 mi (35 km)
  3. Muscatine, IA 22 mi (36 km)
  4. near Rock Island, IL 24 mi (39 km)
  5. Galesburg, IL 26 mi (41 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: 41.1978, -90.7447.