U.S. Frost Dates by Weather Station

NOAA station USC00130385 · Iowa

Frost Dates for Audubon, IA

NOAA weather station Audubon (USC00130385), Iowa · elevation 1280 ft (390 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 15only 1 spring in 10 still has a frost later
  • Typical last frostMay 250% chance of a frost after it
  • Typical first fall frostOctober 350% chance of a frost before it
  • Frost-free season154 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Audubon, IASpring: a frost after April 19 in 9 years out of 10, after May 2 in half of the years, after May 15 in 1 year out of 10. Fall: the first frost comes before September 19 in 1 year out of 10, before October 3 in half of the years, before October 17 in 9 years out of 10. Typical frost-free season: 154 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 2First frost ~Oct 3Frost season at Audubon, IASpring: a frost after April 19 in 9 years out of 10, after May 2 in half of the years, after May 15 in 1 year out of 10. Fall: the first frost comes before September 19 in 1 year out of 10, before October 3 in half of the years, before October 17 in 9 years out of 10. Typical frost-free season: 154 days.JFMAMJJASONDLast frost ~May 2First frost ~Oct 3
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 15September 19
50% (typical)May 2October 3
90% (likely)April 19October 17
Frost-free season (32°F, 50% chance)
154 days
Hard frost (28°F), last in spring, 50% chance after
April 22
Hard frost (28°F), first in fall, 50% chance before
October 14

The last 15 years (2006–2020 normals)

Typical last frost May 2 (same as the 30-year normal), typical first fall frost October 8 (5 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 Audubon: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 15, 20% May 9, 30% May 6, 40% May 4, 50% May 2, 60% April 30, 70% April 27, 80% April 23, 90% April 19. Observed last spring frost in recent years: 2021 May 13, 2022 May 22, 2023 May 4, 2024 April 22, 2026 May 10.Spring: last frostChance of a frost after this date10%50%90%May 1May 15May 2Apr 192021: May 132022: May 222023: May 42024: April 222026: May 10Fall at Audubon: chance of a frost before this dateFall, chance of a frost before the date: 10% September 19, 20% September 24, 30% September 28, 40% October 1, 50% October 3, 60% October 5, 70% October 9, 80% October 13, 90% October 17. Observed first fall frost in recent years: 2021 September 26, 2022 September 28, 2023 October 8, 2024 October 7, 2025 October 23.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 19Oct 3Oct 172021: September 262022: September 282023: October 82024: 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 13September 26
2022May 22September 28
2023May 4October 8
2024April 22October 7
2025incomplete recordOctober 23
2026May 10season not over yet

What these dates mean

May 15 is the cautious spring light-frost date for Audubon; with only a 10 % chance of a frost later, it lets a gardener plan to set out tender crops. The 50% date is May 2, a 50 % chance of a light frost later than this date, while the earlier April 19 date carries a 90 % chance and is a gamble.

In fall, September 19 is the cautious light-frost date, giving a 10 % chance of a frost earlier and marking when tender crops should be finished. The 50% date is October 3, a 50 % chance of a light frost earlier than this date, and the later October 17 date has a 90 % chance, making a late harvest risky. The 50% hard-frost dates are April 22 and October 14; a hard frost at 28 °F can damage plants more severely than a light frost at 32 °F. The record spans 30 years and the interval between the two 32 °F 50% dates is 154 days.

How to read the probabilities

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

  • Spring: "10% after May 15" 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 19" 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 Audubon, IANumbered nearest stations: 1 — Atlantic, IA — 20 mi; 2 — Guthrie Center, IA — 22 mi; 3 — Carroll, IA — 25 mi; 4 — Denison, IA — 31 mi; 5 — Jefferson, IA — 34 mi.IANE25 mi · 40 km1. Atlantic, IA — 20 mi12. Guthrie Center, IA — 22 mi23. Carroll, IA — 25 mi34. Denison, IA — 31 mi45. Jefferson, IA — 34 mi5
  1. Atlantic, IA 20 mi (33 km)
  2. Guthrie Center, IA 22 mi (36 km)
  3. Carroll, IA 25 mi (40 km)
  4. Denison, IA 31 mi (50 km)
  5. Jefferson, IA 34 mi (55 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: 41.7069, -94.9222.