U.S. Frost Dates by Weather Station

NOAA station USC00117391 · Illinois

Frost Dates near Rock Island, IL

NOAA weather station Rock Island Lock and Dam 15 (USC00117391), Illinois · elevation 568 ft (173 m) · hardiness zone 5b*

Rock Island is the nearest town to the station (0.9 mi away) in GeoNames (CC BY 4.0). The dates below are measured at the station, not in the town itself.

  • Lower-risk planting dateafter May 4only 1 spring in 10 still has a frost later
  • Typical last frostApril 1950% chance of a frost after it
  • Typical first fall frostOctober 2250% chance of a frost before it
  • Frost-free season184 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season near Rock Island, ILSpring: a frost after April 6 in 9 years out of 10, after April 19 in half of the years, after May 4 in 1 year out of 10. Fall: the first frost comes before October 7 in 1 year out of 10, before October 22 in half of the years, before November 2 in 9 years out of 10. Typical frost-free season: 184 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 19First frost ~Oct 22Frost season near Rock Island, ILSpring: a frost after April 6 in 9 years out of 10, after April 19 in half of the years, after May 4 in 1 year out of 10. Fall: the first frost comes before October 7 in 1 year out of 10, before October 22 in half of the years, before November 2 in 9 years out of 10. Typical frost-free season: 184 days.JFMAMJJASONDLast frost ~Apr 19First frost ~Oct 22
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.Today

Frost dates (32°F)

Probability of frost, based on 30 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 4October 7
50% (typical)April 19October 22
90% (likely)April 6November 2
Frost-free season (32°F, 50% chance)
184 days
Hard frost (28°F), last in spring, 50% chance after
April 8
Hard frost (28°F), first in fall, 50% chance before
October 31

The last 15 years (2006–2020 normals)

Typical last frost April 21 (2 days later than the 30-year normal), typical first fall frost October 23 (1 day later). Frost-free season 184 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 near Rock Island: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 4, 20% April 29, 30% April 24, 40% April 21, 50% April 19, 60% April 16, 70% April 13, 80% April 10, 90% April 6. Observed last spring frost in recent years: 2021 April 16, 2022 April 26, 2023 April 7, 2024 April 6, 2025 April 8.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 4Apr 19Apr 62021: April 162022: April 262023: April 72024: April 62025: April 8Fall near Rock Island: chance of a frost before this dateFall, chance of a frost before the date: 10% October 7, 20% October 13, 30% October 17, 40% October 19, 50% October 22, 60% October 24, 70% October 27, 80% October 30, 90% November 2. Observed first fall frost in recent years: 2021 November 3, 2022 October 18, 2023 October 30, 2024 November 20.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Oct 7Oct 22Nov 22021: November 32022: October 182023: October 302024: November 20
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 16November 3
2022April 26October 18
2023April 7October 30
2024April 6November 20
2025April 8incomplete record
2026incomplete recordseason not over yet

What these dates mean

May 4, when there is only a 10 % chance of a light frost later, is the cautious date for setting out tender crops in the Rock Island area. After this date a gardener can move seedlings or transplants outdoors with minimal risk of a damaging frost, allowing the growing season to begin confidently.

The 50 % dates—April 19 in spring and October 22 in fall—mark the median point at which a light frost is equally likely to have occurred or not; they are not frost dates but give a sense of the central tendency of the frost window. For hard frost (28 °F), the median dates are April 8 and October 31, reflecting the same even-odds concept for colder freezes. October 7, with a 10 % chance of a light frost earlier, is the cautious date for finishing tender-crop harvests. Because a hard frost reaches a lower temperature, it can injure or kill plants that survive a light frost, making it a more serious threat.

How to read the probabilities

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

  • Spring: "10% after May 4" 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 7" 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 Rock Island, ILNumbered nearest stations: 1 — near Moline, IL — 4 mi; 2 — near Le Claire, IA — 9 mi; 3 — Geneseo, IL — 22 mi; 4 — Aledo, IL — 24 mi; 5 — near Camanche, IA — 25 mi.ILIA25 mi · 40 km1. near Moline, IL — 4 mi12. near Le Claire, IA — 9 mi23. Geneseo, IL — 22 mi34. Aledo, IL — 24 mi45. near Camanche, IA — 25 mi5
  1. near Moline, IL 4 mi (7 km)
  2. near Le Claire, IA 9 mi (15 km)
  3. Geneseo, IL 22 mi (35 km)
  4. Aledo, IL 24 mi (39 km)
  5. near Camanche, IA 25 mi (40 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: 41.5181, -90.5647.