U.S. Frost Dates by Weather Station

NOAA station USC00134389 · Iowa

Frost Dates for Keosauqua, IA

NOAA weather station Keosauqua (USC00134389), Iowa · elevation 629 ft (192 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 11only 1 spring in 10 still has a frost later
  • Typical last frostApril 2650% chance of a frost after it
  • Typical first fall frostOctober 1350% chance of a frost before it
  • Frost-free season169 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Keosauqua, IASpring: a frost after April 10 in 9 years out of 10, after April 26 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 13 in half of the years, before October 26 in 9 years out of 10. Typical frost-free season: 169 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 26First frost ~Oct 13Frost season at Keosauqua, IASpring: a frost after April 10 in 9 years out of 10, after April 26 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 13 in half of the years, before October 26 in 9 years out of 10. Typical frost-free season: 169 days.JFMAMJJASONDLast frost ~Apr 26First frost ~Oct 13
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 26October 13
90% (likely)April 10October 26
Frost-free season (32°F, 50% chance)
169 days
Hard frost (28°F), last in spring, 50% chance after
April 14
Hard frost (28°F), first in fall, 50% chance before
October 23

The last 15 years (2006–2020 normals)

Typical last frost April 24 (2 days earlier than the 30-year normal), typical first fall frost October 18 (5 days later). Frost-free season 176 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 Keosauqua: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 11, 20% May 5, 30% May 2, 40% April 29, 50% April 26, 60% April 23, 70% April 19, 80% April 16, 90% April 10. Observed last spring frost in recent years: 2021 April 23, 2022 April 27, 2023 April 24, 2024 April 21, 2025 April 9, 2026 April 21.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 11Apr 26Apr 102021: April 232022: April 272023: April 242024: April 212025: April 92026: April 21Fall at Keosauqua: 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 10, 50% October 13, 60% October 15, 70% October 19, 80% October 21, 90% October 26. Observed first fall frost in recent years: 2021 November 2, 2022 October 8, 2023 October 28, 2024 October 16, 2025 October 24.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 28Oct 13Oct 262021: November 22022: October 82023: October 282024: October 162025: October 24
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 23November 2
2022April 27October 8
2023April 24October 28
2024April 21October 16
2025April 9October 24
2026April 21season not over yet

What these dates mean

May 11 is the cautious spring date, allowing a gardener to set out tender crops with only a 10 % chance of a light frost later. The 50% date is April 26, meaning a light frost is equally likely to occur after this point in spring. April 14 and October 23 are the 50% dates for hard frost, indicating the median chance of a 28 °F frost at those times.

In the fall, September 28 is the cautious date for finishing the harvest of tender crops, carrying only a 10 % chance that a light frost has arrived earlier. The 50% date is October 13, marking even odds for a light frost occurring before that day. Hard frost at 28 °F can cause far more severe damage to plants than a light frost at 32 °F, so its median dates are especially important for planning.

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 Keosauqua, IANumbered nearest stations: 1 — Fairfield, IA — 20 mi; 2 — Bloomfield, IA — 23 mi; 3 — Mount Pleasant, IA — 26 mi; 4 — Fort Madison, IA — 34 mi; 5 — near Ottumwa, IA — 36 mi.MOIL25 mi · 40 km1. Fairfield, IA — 20 mi12. Bloomfield, IA — 23 mi23. Mount Pleasant, IA — 26 mi34. Fort Madison, IA — 34 mi45. near Ottumwa, IA — 36 mi5
  1. Fairfield, IA 20 mi (32 km)
  2. Bloomfield, IA 23 mi (37 km)
  3. Mount Pleasant, IA 26 mi (41 km)
  4. Fort Madison, IA 34 mi (55 km)
  5. near Ottumwa, IA 36 mi (58 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: 40.7356, -91.9697.