U.S. Frost Dates by Weather Station

NOAA station USC00131233 · Iowa

Frost Dates for Carroll, IA

NOAA weather station Carroll (USC00131233), Iowa · elevation 1240 ft (378 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 8only 1 spring in 10 still has a frost later
  • Typical last frostApril 2750% chance of a frost after it
  • Typical first fall frostOctober 1050% chance of a frost before it
  • Frost-free season166 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Carroll, IASpring: a frost after April 14 in 9 years out of 10, after April 27 in half of the years, after May 8 in 1 year out of 10. Fall: the first frost comes before September 25 in 1 year out of 10, before October 10 in half of the years, before October 24 in 9 years out of 10. Typical frost-free season: 166 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 27First frost ~Oct 10Frost season at Carroll, IASpring: a frost after April 14 in 9 years out of 10, after April 27 in half of the years, after May 8 in 1 year out of 10. Fall: the first frost comes before September 25 in 1 year out of 10, before October 10 in half of the years, before October 24 in 9 years out of 10. Typical frost-free season: 166 days.JFMAMJJASONDLast frost ~Apr 27First 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 30 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 8September 25
50% (typical)April 27October 10
90% (likely)April 14October 24
Frost-free season (32°F, 50% chance)
166 days
Hard frost (28°F), last in spring, 50% chance after
April 16
Hard frost (28°F), first in fall, 50% chance before
October 21

The last 15 years (2006–2020 normals)

Typical last frost April 26 (1 day earlier than the 30-year normal), typical first fall frost October 12 (2 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 Carroll: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 8, 20% May 5, 30% May 2, 40% April 30, 50% April 27, 60% April 24, 70% April 21, 80% April 18, 90% April 14. Observed last spring frost in recent years: 2021 April 23, 2022 April 27, 2023 April 25, 2024 April 22, 2025 April 9, 2026 May 2.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 8Apr 27Apr 142021: April 232022: April 272023: April 252024: April 222025: April 92026: May 2Fall at Carroll: chance of a frost before this dateFall, chance of a frost before the date: 10% September 25, 20% September 29, 30% October 2, 40% October 6, 50% October 10, 60% October 13, 70% October 16, 80% October 20, 90% October 24. Observed first fall frost in recent years: 2021 October 22, 2022 September 28, 2023 October 10, 2024 October 15, 2025 October 23.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 25Oct 10Oct 242021: October 222022: September 282023: 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
2021April 23October 22
2022April 27September 28
2023April 25October 10
2024April 22October 15
2025April 9October 23
2026May 2season not over yet

What these dates mean

Gardeners targeting the end of the season note that the cautious fall date for finishing the harvest in Carroll is September 25, when there is only a 10 % chance that a light frost has arrived.

In spring, the cautious date for setting out tender crops is May 8, which carries a 10 % chance of a frost later than that day, while April 14 carries a 90 % chance and is a gamble. The 50 % dates are April 27 in spring and October 10 in fall; they mark the point at which there is an even chance of a light frost occurring later (spring) or earlier (fall). The median hard-frost dates are April 16 and October 21, and hard frost at 28 °F can damage plants that would survive a light frost at 32 °F, making it a more critical threshold.

How to read the probabilities

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

  • Spring: "10% after May 8" 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 25" 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 Carroll, IANumbered nearest stations: 1 — Jefferson, IA — 24 mi; 2 — Denison, IA — 25 mi; 3 — Audubon, IA — 25 mi; 4 — Sac City, IA — 25 mi; 5 — Rockwell City, IA — 26 mi.NE25 mi · 40 km1. Jefferson, IA — 24 mi12. Denison, IA — 25 mi23. Audubon, IA — 25 mi34. Sac City, IA — 25 mi45. Rockwell City, IA — 26 mi5
  1. Jefferson, IA 24 mi (38 km)
  2. Denison, IA 25 mi (40 km)
  3. Audubon, IA 25 mi (40 km)
  4. Sac City, IA 25 mi (41 km)
  5. Rockwell City, IA 26 mi (41 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: 42.065, -94.85.