U.S. Frost Dates by Weather Station

NOAA station USC00135123 · Iowa

Frost Dates near Mapleton, IA

NOAA weather station Mapleton No.2 (USC00135123), Iowa · elevation 1200 ft (366 m) · hardiness zone 5a*

Mapleton is the nearest town to the station (0.6 mi away) in GeoNames (CC BY 4.0). The dates below are measured at the station, not in the town itself.

  • Lower-risk planting dateafter May 16only 1 spring in 10 still has a frost later
  • Typical last frostMay 350% chance of a frost after it
  • Typical first fall frostOctober 150% chance of a frost before it
  • Frost-free season151 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season near Mapleton, IASpring: a frost after April 21 in 9 years out of 10, after May 3 in half of the years, after May 16 in 1 year out of 10. Fall: the first frost comes before September 19 in 1 year out of 10, before October 1 in half of the years, before October 17 in 9 years out of 10. Typical frost-free season: 151 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 3First frost ~Oct 1Frost season near Mapleton, IASpring: a frost after April 21 in 9 years out of 10, after May 3 in half of the years, after May 16 in 1 year out of 10. Fall: the first frost comes before September 19 in 1 year out of 10, before October 1 in half of the years, before October 17 in 9 years out of 10. Typical frost-free season: 151 days.JFMAMJJASONDLast frost ~May 3First frost ~Oct 1
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 16September 19
50% (typical)May 3October 1
90% (likely)April 21October 17
Frost-free season (32°F, 50% chance)
151 days
Hard frost (28°F), last in spring, 50% chance after
April 24
Hard frost (28°F), first in fall, 50% chance before
October 12

The last 15 years (2006–2020 normals)

Typical last frost May 2 (1 day earlier than the 30-year normal), typical first fall frost October 7 (6 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 near Mapleton: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 16, 20% May 10, 30% May 7, 40% May 5, 50% May 3, 60% April 30, 70% April 28, 80% April 25, 90% April 21. Observed last spring frost in recent years: 2021 May 6, 2022 May 22, 2024 April 25, 2025 April 19, 2026 May 7.Spring: last frostChance of a frost after this date10%50%90%May 1May 16May 3Apr 212021: May 62022: May 222024: April 252025: April 192026: May 7Fall near Mapleton: chance of a frost before this dateFall, chance of a frost before the date: 10% September 19, 20% September 23, 30% September 27, 40% September 29, 50% October 1, 60% October 5, 70% October 7, 80% October 11, 90% October 17. Observed first fall frost in recent years: 2021 October 22, 2022 October 8, 2024 October 7, 2025 October 22.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 19Oct 1Oct 172021: October 222022: October 82024: October 72025: 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
2021May 6October 22
2022May 22October 8
2023incomplete recordincomplete record
2024April 25October 7
2025April 19October 22
2026May 7season not over yet

What these dates mean

May 16 is the cautious spring light-frost date for the Mapleton area; there is a 10 % chance of a frost later than this date, so a gardener can begin setting out tender crops with relatively low risk. In contrast, the early spring date of April 21 carries a 90 % chance of a frost later and is a gamble.

The 50% date is May 3 and means a 50 % chance of a frost later than this date; the 50% date is October 1 and means a 50 % chance of a frost earlier than this date. September 19 is the cautious fall light-frost date, with a 10 % chance of a frost earlier than this date, giving a gardener a reasonable point to finish harvesting tender crops. The hard-frost 50% dates are April 24 and October 12. Hard frost at 28 °F matters more than a light frost because it can damage plants that survive the 32 °F 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 16" 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 Mapleton, IANumbered nearest stations: 1 — Castana Experiment Farm, IA — 7 mi; 2 — Denison, IA — 25 mi; 3 — near Sioux City, IA — 34 mi; 4 — Logan, IA — 36 mi; 5 — Cherokee, IA — 43 mi.IANESD25 mi · 40 km1. Castana Experiment Farm, IA — 7 mi12. Denison, IA — 25 mi23. near Sioux City, IA — 34 mi34. Logan, IA — 36 mi45. Cherokee, IA — 43 mi5
  1. Castana Experiment Farm, IA 7 mi (12 km)
  2. Denison, IA 25 mi (40 km)
  3. near Sioux City, IA 34 mi (55 km)
  4. Logan, IA 36 mi (58 km)
  5. Cherokee, IA 43 mi (69 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: 42.1619, -95.7836.