U.S. Frost Dates by Weather Station

NOAA station USC00118916 · Illinois

Frost Dates for Walnut, IL

NOAA weather station Walnut (USC00118916), Illinois · elevation 671 ft (205 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 9only 1 spring in 10 still has a frost later
  • Typical last frostApril 2450% chance of a frost after it
  • Typical first fall frostOctober 1450% chance of a frost before it
  • Frost-free season172 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Walnut, ILSpring: a frost after April 10 in 9 years out of 10, after April 24 in half of the years, after May 9 in 1 year out of 10. Fall: the first frost comes before September 30 in 1 year out of 10, before October 14 in half of the years, before October 27 in 9 years out of 10. Typical frost-free season: 172 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 24First frost ~Oct 14Frost season at Walnut, ILSpring: a frost after April 10 in 9 years out of 10, after April 24 in half of the years, after May 9 in 1 year out of 10. Fall: the first frost comes before September 30 in 1 year out of 10, before October 14 in half of the years, before October 27 in 9 years out of 10. Typical frost-free season: 172 days.JFMAMJJASONDLast frost ~Apr 24First frost ~Oct 14
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 9September 30
50% (typical)April 24October 14
90% (likely)April 10October 27
Frost-free season (32°F, 50% chance)
172 days
Hard frost (28°F), last in spring, 50% chance after
April 12
Hard frost (28°F), first in fall, 50% chance before
October 24

The last 15 years (2006–2020 normals)

Typical last frost April 24 (same as the 30-year normal), typical first fall frost October 17 (3 days later). Frost-free season 176 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 Walnut: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 9, 20% May 4, 30% April 30, 40% April 27, 50% April 24, 60% April 21, 70% April 18, 80% April 15, 90% April 10. Observed last spring frost in recent years: 2021 April 22, 2022 April 20, 2023 April 26, 2024 April 25, 2025 April 16, 2026 May 2.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 9Apr 24Apr 102021: April 222022: April 202023: April 262024: April 252025: April 162026: May 2Fall at Walnut: chance of a frost before this dateFall, chance of a frost before the date: 10% September 30, 20% October 5, 30% October 8, 40% October 11, 50% October 14, 60% October 16, 70% October 19, 80% October 22, 90% October 27. Observed first fall frost in recent years: 2021 October 23, 2022 October 8, 2023 October 30, 2024 October 15, 2025 October 23.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 30Oct 14Oct 272021: October 232022: October 82023: October 302024: October 152025: October 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 22October 23
2022April 20October 8
2023April 26October 30
2024April 25October 15
2025April 16October 23
2026May 2season not over yet

What these dates mean

Setting out tender crops on the early spring date of April 10 carries a 90 % chance of a frost later, so it is a gamble for Walnut gardeners. The cautious spring date is May 9, when only a 10 % chance of a later frost remains. In the fall, the cautious date to finish harvesting tender crops is September 30, with only a 10 % chance that a frost has already arrived, while counting on crops through October 27 would be a gamble.

The 50 % dates—April 24 in spring and October 14 in fall—mark the point where the odds of a light frost are even; a gardener has a 50 % chance of a frost later than April 24 and a 50 % chance of a frost earlier than October 14. The hard-frost median dates are April 12 and October 24, and a hard frost at 28 °F can injure plants that would otherwise survive a light frost at 32 °F.

How to read the probabilities

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

  • Spring: "10% after May 9" 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 September 30" 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 Walnut, ILNumbered nearest stations: 1 — Princeton, IL — 16 mi; 2 — Morrison, IL — 25 mi; 3 — Kewanee, IL — 27 mi; 4 — Geneseo, IL — 29 mi; 5 — Peru, IL — 29 mi.IA25 mi · 40 km1. Princeton, IL — 16 mi12. Morrison, IL — 25 mi23. Kewanee, IL — 27 mi34. Geneseo, IL — 29 mi45. Peru, IL — 29 mi5
  1. Princeton, IL 16 mi (25 km)
  2. Morrison, IL 25 mi (40 km)
  3. Kewanee, IL 27 mi (43 km)
  4. Geneseo, IL 29 mi (47 km)
  5. Peru, IL 29 mi (47 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: 41.5603, -89.6025.