U.S. Frost Dates by Weather Station

NOAA station USC00115833 · Illinois

Frost Dates for Morrison, IL

NOAA weather station Morrison (USC00115833), Illinois · elevation 632 ft (193 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 11only 1 spring in 10 still has a frost later
  • Typical last frostApril 2650% chance of a frost after it
  • Typical first fall frostOctober 1350% chance of a frost before it
  • Frost-free season167 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Morrison, ILSpring: a frost after April 13 in 9 years out of 10, after April 26 in half of the years, after May 11 in 1 year out of 10. Fall: the first frost comes before September 30 in 1 year out of 10, before October 13 in half of the years, before October 25 in 9 years out of 10. Typical frost-free season: 167 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 26First frost ~Oct 13Frost season at Morrison, ILSpring: a frost after April 13 in 9 years out of 10, after April 26 in half of the years, after May 11 in 1 year out of 10. Fall: the first frost comes before September 30 in 1 year out of 10, before October 13 in half of the years, before October 25 in 9 years out of 10. Typical frost-free season: 167 days.JFMAMJJASONDLast frost ~Apr 26First frost ~Oct 13
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 27 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 11September 30
50% (typical)April 26October 13
90% (likely)April 13October 25
Frost-free season (32°F, 50% chance)
167 days
Hard frost (28°F), last in spring, 50% chance after
April 15
Hard frost (28°F), first in fall, 50% chance before
October 23

The last 15 years (2006–2020 normals)

Typical last frost April 26 (same as the 30-year normal), typical first fall frost October 16 (3 days later). Frost-free season 171 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 Morrison: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 11, 20% May 6, 30% May 2, 40% April 29, 50% April 26, 60% April 23, 70% April 20, 80% April 17, 90% April 13. Observed last spring frost in recent years: 2021 May 12, 2022 April 28, 2023 April 27, 2024 April 22, 2025 April 16, 2026 May 7.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 11Apr 26Apr 132021: May 122022: April 282023: April 272024: April 222025: April 162026: May 7Fall at Morrison: chance of a frost before this dateFall, chance of a frost before the date: 10% September 30, 20% October 5, 30% October 9, 40% October 11, 50% October 13, 60% October 15, 70% October 18, 80% October 21, 90% October 25. Observed first fall frost in recent years: 2021 October 23, 2022 October 8, 2023 October 10, 2024 October 15, 2025 October 23.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 30Oct 13Oct 252021: October 232022: October 82023: October 102024: 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
2021May 12October 23
2022April 28October 8
2023April 27October 10
2024April 22October 15
2025April 16October 23
2026May 7season not over yet

What these dates mean

The 167 days between the 50% dates in Morrison frame the period when tender crops can most reliably be out of frost danger. The 50% light-frost dates are April 26 and October 13, meaning there is an even chance of a frost either side of each date. The 50% hard-frost dates are April 15 and October 23, marking the point at which a temperature of 28 °F is equally likely.

For a cautious spring schedule, gardeners should wait until the May 11 light-frost date, which carries only a 10 % chance of a later frost, before setting out tender crops. In the fall, the September 30 light-frost date is the cautious marker, offering only a 10 % chance that a frost has already arrived, making it the preferred time to finish harvesting tender crops. A hard frost matters more than a light frost because the colder 28 °F threshold can damage plant tissue that survives a 32 °F event.

How to read the probabilities

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

  • Spring: "10% after May 11" 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 Morrison, ILNumbered nearest stations: 1 — near Camanche, IA — 15 mi; 2 — Walnut, IL — 25 mi; 3 — Geneseo, IL — 25 mi; 4 — near Le Claire, IA — 27 mi; 5 — near Rock Island, IL — 36 mi.ILIA25 mi · 40 km1. near Camanche, IA — 15 mi12. Walnut, IL — 25 mi23. Geneseo, IL — 25 mi34. near Le Claire, IA — 27 mi45. near Rock Island, IL — 36 mi5
  1. near Camanche, IA 15 mi (25 km)
  2. Walnut, IL 25 mi (40 km)
  3. Geneseo, IL 25 mi (41 km)
  4. near Le Claire, IA 27 mi (43 km)
  5. near Rock Island, IL 36 mi (58 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: 41.7944, -89.9681.