U.S. Frost Dates by Weather Station

NOAA station USC00117077 · Illinois

Frost Dates for Quincy Dam 21, IL

NOAA weather station Quincy Dam 21 (USC00117077), Illinois · elevation 483 ft (147 m) · hardiness zone 6a*

  • Lower-risk planting dateafter April 23only 1 spring in 10 still has a frost later
  • Typical last frostApril 850% chance of a frost after it
  • Typical first fall frostOctober 3050% chance of a frost before it
  • Frost-free season204 daystypical year, 32°F
  • Hardiness zone6acalculated*

The year at a glance

Frost season at Quincy Dam 21, ILSpring: a frost after March 24 in 9 years out of 10, after April 8 in half of the years, after April 23 in 1 year out of 10. Fall: the first frost comes before October 17 in 1 year out of 10, before October 30 in half of the years, before November 10 in 9 years out of 10. Typical frost-free season: 204 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 8First frost ~Oct 30Frost season at Quincy Dam 21, ILSpring: a frost after March 24 in 9 years out of 10, after April 8 in half of the years, after April 23 in 1 year out of 10. Fall: the first frost comes before October 17 in 1 year out of 10, before October 30 in half of the years, before November 10 in 9 years out of 10. Typical frost-free season: 204 days.JFMAMJJASONDLast frost ~Apr 8First frost ~Oct 30
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 26 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)April 23October 17
50% (typical)April 8October 30
90% (likely)March 24November 10
Frost-free season (32°F, 50% chance)
204 days
Hard frost (28°F), last in spring, 50% chance after
March 30
Hard frost (28°F), first in fall, 50% chance before
November 8

The last 15 years (2006–2020 normals)

Typical last frost April 7 (1 day earlier than the 30-year normal), typical first fall frost October 31 (1 day later). Frost-free season 206 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 Quincy Dam 21: chance of a frost after this dateSpring, chance of a frost after the date: 10% April 23, 20% April 18, 30% April 15, 40% April 11, 50% April 8, 60% April 5, 70% April 3, 80% March 31, 90% March 24. Observed last spring frost in recent years: 2021 April 23, 2024 March 29, 2025 April 9.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1Apr 23Apr 8Mar 242021: April 232024: March 292025: April 9Fall at Quincy Dam 21: chance of a frost before this dateFall, chance of a frost before the date: 10% October 17, 20% October 21, 30% October 25, 40% October 27, 50% October 30, 60% November 1, 70% November 3, 80% November 5, 90% November 10. Observed first fall frost in recent years: 2021 November 3, 2022 October 18, 2023 October 30, 2024 November 23.Fall: first frostChance of a frost before this date10%50%90%Nov 1Oct 17Oct 30Nov 102021: November 32022: October 182023: October 302024: November 23
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 3
2022incomplete recordOctober 18
2023incomplete recordOctober 30
2024March 29November 23
2025April 9incomplete record
2026incomplete recordseason not over yet

What these dates mean

October 17 is the cautious fall date for Quincy Dam 21, the point at which there is only a 10 % chance that a light frost has arrived and tender crops should be finished before then. Waiting beyond this date puts the harvest at a higher risk of frost damage.

For a gardener, the 50 % dates mark the moments when a light frost is equally likely to occur later (April 8 in spring) or earlier (October 30 in fall). The cautious spring plan uses April 23, the date with a 10 % chance of a frost later, while the cautious fall plan relies on October 17. These dates give clear reference points for timing tender-crop activities.

A hard frost at 28 °F is more damaging than a light frost at 32 °F because plants that can survive the milder temperature often cannot endure the colder threshold.

How to read the probabilities

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

  • Spring: "10% after April 23" 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 17" 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 Quincy Dam 21, ILNumbered nearest stations: 1 — Quincy, IL — 13 mi; 2 — Hannibal, MO — 13 mi; 3 — near Canton, MO — 17 mi; 4 — Saverton Lock and Dam 22, MO — 21 mi; 5 — Steffenville, MO — 25 mi.MOILIA25 mi · 40 km1. Quincy, IL — 13 mi12. Hannibal, MO — 13 mi23. near Canton, MO — 17 mi34. Saverton Lock and Dam 22, MO — 21 mi45. Steffenville, MO — 25 mi5
  1. Quincy, IL 13 mi (20 km)
  2. Hannibal, MO 13 mi (21 km)
  3. near Canton, MO 17 mi (28 km)
  4. Saverton Lock and Dam 22, MO 21 mi (33 km)
  5. Steffenville, MO 25 mi (40 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: 39.9036, -91.4283.