U.S. Frost Dates by Weather Station

NOAA station USC00118020 · Illinois

Frost Dates for Smithland Lock and Dam, IL

NOAA weather station Smithland Lock and Dam (USC00118020), Illinois · elevation 357 ft (109 m) · hardiness zone 7a*

  • Lower-risk planting dateafter April 21only 1 spring in 10 still has a frost later
  • Typical last frostApril 350% chance of a frost after it
  • Typical first fall frostOctober 3050% chance of a frost before it
  • Frost-free season207 daystypical year, 32°F
  • Hardiness zone7acalculated*

The year at a glance

Frost season at Smithland Lock and Dam, ILSpring: a frost after March 18 in 9 years out of 10, after April 3 in half of the years, after April 21 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 12 in 9 years out of 10. Typical frost-free season: 207 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 3First frost ~Oct 30Frost season at Smithland Lock and Dam, ILSpring: a frost after March 18 in 9 years out of 10, after April 3 in half of the years, after April 21 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 12 in 9 years out of 10. Typical frost-free season: 207 days.JFMAMJJASONDLast frost ~Apr 3First 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 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)April 21October 17
50% (typical)April 3October 30
90% (likely)March 18November 12
Frost-free season (32°F, 50% chance)
207 days
Hard frost (28°F), last in spring, 50% chance after
March 23
Hard frost (28°F), first in fall, 50% chance before
November 8

The last 15 years (2006–2020 normals)

Typical last frost April 3 (same as the 30-year normal), typical first fall frost October 30. Frost-free season 207 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 Smithland Lock and Dam: chance of a frost after this dateSpring, chance of a frost after the date: 10% April 21, 20% April 14, 30% April 10, 40% April 6, 50% April 3, 60% March 31, 70% March 28, 80% March 24, 90% March 18. Observed last spring frost in recent years: 2021 April 22, 2022 March 21, 2023 March 21, 2024 April 7, 2025 March 22, 2026 March 18.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1Apr 21Apr 3Mar 182021: April 222022: March 212023: March 212024: April 72025: March 222026: March 18Fall at Smithland Lock and Dam: chance of a frost before this dateFall, chance of a frost before the date: 10% October 17, 20% October 22, 30% October 25, 40% October 28, 50% October 30, 60% November 1, 70% November 4, 80% November 7, 90% November 12. Observed first fall frost in recent years: 2021 November 4, 2023 October 31, 2024 October 17, 2025 November 10.Fall: first frostChance of a frost before this date10%50%90%Nov 1Oct 17Oct 30Nov 122021: November 42023: October 312024: October 172025: November 10
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 4
2022March 21incomplete record
2023March 21October 31
2024April 7October 17
2025March 22November 10
2026March 18season not over yet

What these dates mean

October 17 is the cautious fall date for finishing the harvest of tender crops at Smithland Lock and Dam, with only a ten percent chance that a light frost has arrived earlier.

In spring the cautious date for setting out tender crops is April 21, when the risk of a later light frost is low; planting on April 3, the 50% date, means there is an even chance of a frost later, while March 18 carries a ninety percent chance of a frost later and is a gamble. The 50% dates—April 3 and October 30—signal the median point where a light frost is equally likely to occur before or after, giving gardeners a neutral reference for timing.

Hard frost at 28°F can cause damage that a light frost at 32°F often does not, so the median hard-frost dates of March 23 and November 8 are especially relevant.

How to read the probabilities

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

  • Spring: "10% after April 21" 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 Smithland Lock and Dam, ILNumbered nearest stations: 1 — near Metropolis, IL — 12 mi; 2 — Paducah, KY — 20 mi; 3 — Rosiclare, IL — 21 mi; 4 — Princeton, KY — 31 mi; 5 — Murray, KY — 39 mi.TNILMO25 mi · 40 km1. near Metropolis, IL — 12 mi12. Paducah, KY — 20 mi23. Rosiclare, IL — 21 mi34. Princeton, KY — 31 mi45. Murray, KY — 39 mi5
  1. near Metropolis, IL 12 mi (20 km)
  2. Paducah, KY 20 mi (32 km)
  3. Rosiclare, IL 21 mi (35 km)
  4. Princeton, KY 31 mi (50 km)
  5. Murray, KY 39 mi (62 km)

Sources

* Hardiness zone 7a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 37.1644, -88.4311.