U.S. Frost Dates by Weather Station

NOAA station USC00130241 · Iowa

Frost Dates for Ankeny, IA

NOAA weather station Ankeny (USC00130241), Iowa · elevation 975 ft (297 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 6only 1 spring in 10 still has a frost later
  • Typical last frostApril 2350% chance of a frost after it
  • Typical first fall frostOctober 1550% chance of a frost before it
  • Frost-free season173 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Ankeny, IASpring: a frost after April 8 in 9 years out of 10, after April 23 in half of the years, after May 6 in 1 year out of 10. Fall: the first frost comes before September 30 in 1 year out of 10, before October 15 in half of the years, before October 28 in 9 years out of 10. Typical frost-free season: 173 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 23First frost ~Oct 15Frost season at Ankeny, IASpring: a frost after April 8 in 9 years out of 10, after April 23 in half of the years, after May 6 in 1 year out of 10. Fall: the first frost comes before September 30 in 1 year out of 10, before October 15 in half of the years, before October 28 in 9 years out of 10. Typical frost-free season: 173 days.JFMAMJJASONDLast frost ~Apr 23First frost ~Oct 15
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 27 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 6September 30
50% (typical)April 23October 15
90% (likely)April 8October 28
Frost-free season (32°F, 50% chance)
173 days
Hard frost (28°F), last in spring, 50% chance after
April 13
Hard frost (28°F), first in fall, 50% chance before
October 25

The last 15 years (2006–2020 normals)

Typical last frost April 21 (2 days earlier than the 30-year normal), typical first fall frost October 17 (2 days later). Frost-free season 178 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 Ankeny: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 6, 20% May 2, 30% April 29, 40% April 25, 50% April 23, 60% April 19, 70% April 16, 80% April 13, 90% April 8.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 6Apr 23Apr 8Fall at Ankeny: chance of a frost before this dateFall, chance of a frost before the date: 10% September 30, 20% October 5, 30% October 9, 40% October 12, 50% October 15, 60% October 18, 70% October 20, 80% October 23, 90% October 28.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 30Oct 15Oct 28
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.

What these dates mean

May 6 is the cautious spring date for light frost, giving a gardener a ten-percent chance that a frost will occur later and therefore marking a reliable point to set out tender crops. The median light-frost date, April 23, represents an even odds point for when a frost might appear, while the hard-frost median, April 13, indicates the day a fifty-percent chance of temperatures reaching 28 °F occurs. In the fall, September 30 is the cautious date, with only a ten-percent chance that a frost has arrived earlier, making it the sensible time to finish harvesting tender crops. The median light-frost date for autumn is October 15, and the hard-frost median is October 25, each showing a fifty-percent likelihood of their respective temperature thresholds. A hard frost at 28 °F can damage plant tissue that would survive a light frost at 32 °F.

How to read the probabilities

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

  • Spring: "10% after May 6" 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 30" 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 Ankeny, IANumbered nearest stations: 1 — Des Moines, IA — 14 mi; 2 — Ames, IA — 21 mi; 3 — Boone, IA — 25 mi; 4 — Perry, IA — 25 mi; 5 — Indianola, IA — 25 mi.IA25 mi · 40 km1. Des Moines, IA — 14 mi12. Ames, IA — 21 mi23. Boone, IA — 25 mi34. Perry, IA — 25 mi45. Indianola, IA — 25 mi5
  1. Des Moines, IA 14 mi (22 km)
  2. Ames, IA 21 mi (34 km)
  3. Boone, IA 25 mi (40 km)
  4. Perry, IA 25 mi (40 km)
  5. Indianola, IA 25 mi (41 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: 41.7322, -93.65.