U.S. Frost Dates by Weather Station

NOAA station USC00112223 · Illinois

Frost Dates for De Kalb, IL

NOAA weather station De Kalb (USC00112223), Illinois · elevation 873 ft (266 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 10only 1 spring in 10 still has a frost later
  • Typical last frostApril 2450% chance of a frost after it
  • Typical first fall frostOctober 1850% chance of a frost before it
  • Frost-free season177 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at De Kalb, ILSpring: a frost after April 9 in 9 years out of 10, after April 24 in half of the years, after May 10 in 1 year out of 10. Fall: the first frost comes before October 4 in 1 year out of 10, before October 18 in half of the years, before October 31 in 9 years out of 10. Typical frost-free season: 177 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 24First frost ~Oct 18Frost season at De Kalb, ILSpring: a frost after April 9 in 9 years out of 10, after April 24 in half of the years, after May 10 in 1 year out of 10. Fall: the first frost comes before October 4 in 1 year out of 10, before October 18 in half of the years, before October 31 in 9 years out of 10. Typical frost-free season: 177 days.JFMAMJJASONDLast frost ~Apr 24First frost ~Oct 18
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 10October 4
50% (typical)April 24October 18
90% (likely)April 9October 31
Frost-free season (32°F, 50% chance)
177 days
Hard frost (28°F), last in spring, 50% chance after
April 13
Hard frost (28°F), first in fall, 50% chance before
October 28

The last 15 years (2006–2020 normals)

Typical last frost April 23 (1 day earlier than the 30-year normal), typical first fall frost October 21 (3 days later). Frost-free season 180 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 De Kalb: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 10, 20% May 4, 30% April 30, 40% April 27, 50% April 24, 60% April 21, 70% April 17, 80% April 14, 90% April 9. Observed last spring frost in recent years: 2022 April 28, 2023 April 26, 2024 April 25, 2025 April 17, 2026 May 7.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 10Apr 24Apr 92022: April 282023: April 262024: April 252025: April 172026: May 7Fall at De Kalb: chance of a frost before this dateFall, chance of a frost before the date: 10% October 4, 20% October 9, 30% October 13, 40% October 15, 50% October 18, 60% October 21, 70% October 23, 80% October 26, 90% October 31. Observed first fall frost in recent years: 2022 October 8, 2023 October 30, 2024 October 16, 2025 October 24.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Oct 4Oct 18Oct 312022: October 82023: 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
2021incomplete recordincomplete record
2022April 28October 8
2023April 26October 30
2024April 25October 16
2025April 17October 24
2026May 7season not over yet

What these dates mean

October 4 is the cautious fall date in De Kalb for finishing the harvest of tender crops; only a 10 % chance of a light frost has arrived by then. In spring the cautious date for setting out tender crops is May 10, when a frost later than that date occurs only 10 % of the time, while planting on April 9 carries a 90 % gamble.

The 50 % light-frost dates are April 24 in spring and October 18 in fall; each marks the point at which a light frost is equally likely to have occurred or not. The 50 % hard-frost dates are April 13 and October 28, indicating when a temperature of 28 °F is as likely as not.

Hard frost at 28 °F can injure or kill plants that survive a light frost at 32 °F, so it represents a higher risk.

How to read the probabilities

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

  • Spring: "10% after May 10" 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 4" 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 De Kalb, ILNumbered nearest stations: 1 — Rochelle, IL — 15 mi; 2 — Paw Paw, IL — 21 mi; 3 — Rockford, IL — 24 mi; 4 — Aurora, IL — 26 mi; 5 — Elgin, IL — 27 mi.WIIN25 mi · 40 km1. Rochelle, IL — 15 mi12. Paw Paw, IL — 21 mi23. Rockford, IL — 24 mi34. Aurora, IL — 26 mi45. Elgin, IL — 27 mi5
  1. Rochelle, IL 15 mi (25 km)
  2. Paw Paw, IL 21 mi (34 km)
  3. Rockford, IL 24 mi (39 km)
  4. Aurora, IL 26 mi (42 km)
  5. Elgin, IL 27 mi (43 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: 41.9342, -88.7756.