U.S. Frost Dates by Weather Station

NOAA station USC00130807 · Iowa

Frost Dates for Boone, IA

NOAA weather station Boone (USC00130807), Iowa · elevation 1035 ft (316 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 1250% chance of a frost before it
  • Frost-free season165 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Boone, 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 28 in 1 year out of 10, before October 12 in half of the years, before October 25 in 9 years out of 10. Typical frost-free season: 165 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 28First frost ~Oct 12Frost season at Boone, 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 28 in 1 year out of 10, before October 12 in half of the years, before October 25 in 9 years out of 10. Typical frost-free season: 165 days.JFMAMJJASONDLast frost ~Apr 28First frost ~Oct 12
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 11September 28
50% (typical)April 28October 12
90% (likely)April 13October 25
Frost-free season (32°F, 50% chance)
165 days
Hard frost (28°F), last in spring, 50% chance after
April 16
Hard frost (28°F), first in fall, 50% chance before
October 22

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 (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 Boone: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 11, 20% May 6, 30% May 3, 40% April 30, 50% April 28, 60% April 24, 70% April 21, 80% April 18, 90% April 13. Observed last spring frost in recent years: 2021 April 22, 2022 April 27, 2023 May 3, 2024 April 22, 2025 April 9, 2026 May 3.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 11Apr 28Apr 132021: April 222022: April 272023: May 32024: April 222025: April 92026: May 3Fall at Boone: chance of a frost before this dateFall, chance of a frost before the date: 10% September 28, 20% October 2, 30% October 6, 40% October 9, 50% October 12, 60% October 14, 70% October 18, 80% October 21, 90% October 25. Observed first fall frost in recent years: 2021 October 22, 2022 September 28, 2023 October 10, 2024 October 14, 2025 October 22.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 28Oct 12Oct 252021: October 222022: September 282023: October 102024: October 142025: October 22
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 22October 22
2022April 27September 28
2023May 3October 10
2024April 22October 14
2025April 9October 22
2026May 3season not over yet

What these dates mean

In Boone, the cautious spring light-frost date is May 11, when there is only a 10 % chance of a frost later; this date lets a gardener plan to set out tender crops with minimal risk. The cautious fall light-frost date is September 28, which carries a 10 % chance of a frost earlier and therefore marks the point to finish harvesting tender crops.

Between those periods the 50 % light-frost dates are April 28 and October 12; at each of those dates the chance of a frost is evenly split, giving a clear benchmark for when frost risk is at its median. The hard-frost 50 % dates are April 16 in spring and October 22 in fall, dates that are important because a hard frost at 28 °F can damage plant tissue that survives a light frost at 32 °F. The record spans 30 years, and the interval between the two 32 °F 50 % dates is 165 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 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 28" 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 Boone, IANumbered nearest stations: 1 — Ames, IA — 6 mi; 2 — Perry, IA — 18 mi; 3 — Ankeny, IA — 25 mi; 4 — Jefferson, IA — 26 mi; 5 — Webster City, IA — 30 mi.25 mi · 40 km1. Ames, IA — 6 mi12. Perry, IA — 18 mi23. Ankeny, IA — 25 mi34. Jefferson, IA — 26 mi45. Webster City, IA — 30 mi5
  1. Ames, IA 6 mi (10 km)
  2. Perry, IA 18 mi (29 km)
  3. Ankeny, IA 25 mi (40 km)
  4. Jefferson, IA 26 mi (42 km)
  5. Webster City, IA 30 mi (48 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: 42.0417, -93.8908.