U.S. Frost Dates by Weather Station

NOAA station USC00131394 · Iowa

Frost Dates for Chariton, IA

NOAA weather station Chariton 1 E (USC00131394), Iowa · elevation 965 ft (294 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 19only 1 spring in 10 still has a frost later
  • Typical last frostMay 550% chance of a frost after it
  • Typical first fall frostOctober 550% chance of a frost before it
  • Frost-free season151 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Chariton, IASpring: a frost after April 21 in 9 years out of 10, after May 5 in half of the years, after May 19 in 1 year out of 10. Fall: the first frost comes before September 20 in 1 year out of 10, before October 5 in half of the years, before October 18 in 9 years out of 10. Typical frost-free season: 151 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 5First frost ~Oct 5Frost season at Chariton, IASpring: a frost after April 21 in 9 years out of 10, after May 5 in half of the years, after May 19 in 1 year out of 10. Fall: the first frost comes before September 20 in 1 year out of 10, before October 5 in half of the years, before October 18 in 9 years out of 10. Typical frost-free season: 151 days.JFMAMJJASONDLast frost ~May 5First frost ~Oct 5
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 19September 20
50% (typical)May 5October 5
90% (likely)April 21October 18
Frost-free season (32°F, 50% chance)
151 days
Hard frost (28°F), last in spring, 50% chance after
April 26
Hard frost (28°F), first in fall, 50% chance before
October 16

The last 15 years (2006–2020 normals)

Typical last frost May 5 (same as the 30-year normal), typical first fall frost October 11 (6 days later). Frost-free season 157 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 Chariton: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 19, 20% May 14, 30% May 10, 40% May 7, 50% May 5, 60% May 2, 70% April 30, 80% April 26, 90% April 21. Observed last spring frost in recent years: 2021 May 13, 2022 May 2, 2023 May 4, 2024 April 25, 2026 May 10.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 19May 5Apr 212021: May 132022: May 22023: May 42024: April 252026: May 10Fall at Chariton: chance of a frost before this dateFall, chance of a frost before the date: 10% September 20, 20% September 25, 30% September 29, 40% October 1, 50% October 5, 60% October 8, 70% October 11, 80% October 14, 90% October 18. Observed first fall frost in recent years: 2021 October 22, 2022 September 29, 2023 October 9, 2024 October 7, 2025 October 23.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 20Oct 5Oct 182021: October 222022: September 292023: October 92024: October 72025: 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 13October 22
2022May 2September 29
2023May 4October 9
2024April 25October 7
2025incomplete recordOctober 23
2026May 10season not over yet

What these dates mean

September 20 marks the cautious fall date for finishing the harvest in Chariton, Iowa; there is a 10 % chance that a light frost has arrived earlier. Tender crops planted after that date face a high risk of frost damage.

In spring, the cautious date for setting out tender crops is May 19, when a light frost still has a 10 % chance of occurring later. The 50 % light-frost date is May 5, meaning there is an even chance of a frost later than that date. The median hard-frost date is April 26, indicating a 50 % chance of temperatures reaching 28 °F.

Fall’s cautious date is September 20, while the 50 % light-frost date is October 5, meaning there is an even chance of a frost earlier than that date, and the median hard-frost date is October 16. A hard frost of 28 °F can damage plants that survive a light frost of 32 °F, so it poses a greater 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 19" 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 20" 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 Chariton, IANumbered nearest stations: 1 — Osceola, IA — 25 mi; 2 — Albia, IA — 26 mi; 3 — Indianola, IA — 31 mi; 4 — Oskaloosa, IA — 39 mi; 5 — Des Moines, IA — 41 mi.IA25 mi · 40 km1. Osceola, IA — 25 mi12. Albia, IA — 26 mi23. Indianola, IA — 31 mi34. Oskaloosa, IA — 39 mi45. Des Moines, IA — 41 mi5
  1. Osceola, IA 25 mi (40 km)
  2. Albia, IA 26 mi (42 km)
  3. Indianola, IA 31 mi (50 km)
  4. Oskaloosa, IA 39 mi (63 km)
  5. Des Moines, IA 41 mi (65 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: 41.0164, -93.2792.