U.S. Frost Dates by Weather Station

NOAA station USC00134142 · Iowa

Frost Dates for Iowa Falls, IA

NOAA weather station Iowa Falls (USC00134142), Iowa · elevation 1055 ft (322 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 11only 1 spring in 10 still has a frost later
  • Typical last frostApril 2850% chance of a frost after it
  • Typical first fall frostOctober 1050% chance of a frost before it
  • Frost-free season164 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Iowa Falls, IASpring: a frost after April 13 in 9 years out of 10, after April 28 in half of the years, after May 11 in 1 year out of 10. Fall: the first frost comes before September 26 in 1 year out of 10, before October 10 in half of the years, before October 22 in 9 years out of 10. Typical frost-free season: 164 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 28First frost ~Oct 10Frost season at Iowa Falls, IASpring: a frost after April 13 in 9 years out of 10, after April 28 in half of the years, after May 11 in 1 year out of 10. Fall: the first frost comes before September 26 in 1 year out of 10, before October 10 in half of the years, before October 22 in 9 years out of 10. Typical frost-free season: 164 days.JFMAMJJASONDLast frost ~Apr 28First frost ~Oct 10
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 11September 26
50% (typical)April 28October 10
90% (likely)April 13October 22
Frost-free season (32°F, 50% chance)
164 days
Hard frost (28°F), last in spring, 50% chance after
April 17
Hard frost (28°F), first in fall, 50% chance before
October 20

The last 15 years (2006–2020 normals)

Typical last frost April 29 (1 day later than the 30-year normal), typical first fall frost October 14 (4 days later). Frost-free season 169 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 Iowa Falls: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 11, 20% May 7, 30% May 3, 40% May 1, 50% April 28, 60% April 25, 70% April 22, 80% April 17, 90% April 13. Observed last spring frost in recent years: 2021 May 12, 2022 April 27, 2023 May 3, 2024 April 22, 2025 April 17, 2026 May 2.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 11Apr 28Apr 132021: May 122022: April 272023: May 32024: April 222025: April 172026: May 2Fall at Iowa Falls: chance of a frost before this dateFall, chance of a frost before the date: 10% September 26, 20% October 1, 30% October 4, 40% October 7, 50% October 10, 60% October 13, 70% October 15, 80% October 18, 90% October 22. Observed first fall frost in recent years: 2021 October 22, 2022 October 8, 2023 October 30, 2024 October 15, 2025 October 23.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 26Oct 10Oct 222021: October 222022: October 82023: October 302024: 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 22
2022April 27October 8
2023May 3October 30
2024April 22October 15
2025April 17October 23
2026May 2season not over yet

What these dates mean

September 26 is the cautious fall date for finishing the harvest in Iowa Falls; there is only a 10 % chance that a light frost has arrived earlier, so tender crops are most likely still safe to pick.

For spring planting, the cautious date is May 11, when a light frost later than that day occurs with just a 10 % chance; planting before April 13 would be a gamble because a frost later than that date is 90 % likely. The 50 % date in spring is April 28, giving a 50 % chance of a light frost later than this date, while the 50 % date in fall is October 10, with a 50 % chance of a light frost earlier than this date.

Hard-frost median dates are April 17 in spring and October 20 in fall, and hard frost matters more than light frost because the lower temperature can cause far greater damage to plants.

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 26" 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 Iowa Falls, IANumbered nearest stations: 1 — Eldora, IA — 13 mi; 2 — Hampton, IA — 17 mi; 3 — Grundy Center, IA — 27 mi; 4 — Webster City, IA — 28 mi; 5 — Allison, IA — 28 mi.25 mi · 40 km1. Eldora, IA — 13 mi12. Hampton, IA — 17 mi23. Grundy Center, IA — 27 mi34. Webster City, IA — 28 mi45. Allison, IA — 28 mi5
  1. Eldora, IA 13 mi (21 km)
  2. Hampton, IA 17 mi (27 km)
  3. Grundy Center, IA 27 mi (44 km)
  4. Webster City, IA 28 mi (45 km)
  5. Allison, IA 28 mi (45 km)

Sources

* Hardiness zone 5a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 42.5189, -93.2536.