U.S. Frost Dates by Weather Station

NOAA station USC00134101 · Iowa

Frost Dates for Iowa City, IA

NOAA weather station Iowa City (USC00134101), Iowa · elevation 640 ft (195 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 14only 1 spring in 10 still has a frost later
  • Typical last frostApril 2950% chance of a frost after it
  • Typical first fall frostOctober 950% chance of a frost before it
  • Frost-free season162 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Iowa City, IASpring: a frost after April 14 in 9 years out of 10, after April 29 in half of the years, after May 14 in 1 year out of 10. Fall: the first frost comes before September 25 in 1 year out of 10, before October 9 in half of the years, before October 22 in 9 years out of 10. Typical frost-free season: 162 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 29First frost ~Oct 9Frost season at Iowa City, IASpring: a frost after April 14 in 9 years out of 10, after April 29 in half of the years, after May 14 in 1 year out of 10. Fall: the first frost comes before September 25 in 1 year out of 10, before October 9 in half of the years, before October 22 in 9 years out of 10. Typical frost-free season: 162 days.JFMAMJJASONDLast frost ~Apr 29First frost ~Oct 9
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 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 14September 25
50% (typical)April 29October 9
90% (likely)April 14October 22
Frost-free season (32°F, 50% chance)
162 days
Hard frost (28°F), last in spring, 50% chance after
April 18
Hard frost (28°F), first in fall, 50% chance before
October 20

The last 15 years (2006–2020 normals)

Typical last frost April 29 (same as the 30-year normal), typical first fall frost October 12 (3 days later). Frost-free season 166 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 Iowa City: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 14, 20% May 8, 30% May 5, 40% May 1, 50% April 29, 60% April 26, 70% April 23, 80% April 18, 90% April 14. Observed last spring frost in recent years: 2021 April 26, 2022 April 27, 2023 April 26, 2024 April 22, 2025 April 16, 2026 May 7.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 14Apr 29Apr 142021: April 262022: April 272023: April 262024: April 222025: April 162026: May 7Fall at Iowa City: chance of a frost before this dateFall, chance of a frost before the date: 10% September 25, 20% September 30, 30% October 3, 40% October 6, 50% October 9, 60% October 12, 70% October 15, 80% October 18, 90% October 22. Observed first fall frost in recent years: 2021 October 23, 2022 October 8, 2023 October 10, 2024 October 16, 2025 October 23.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 25Oct 9Oct 222021: October 232022: October 82023: October 102024: October 162025: 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
2021April 26October 23
2022April 27October 8
2023April 26October 10
2024April 22October 16
2025April 16October 23
2026May 7season not over yet

What these dates mean

In Iowa City, planting tender crops on the early spring date of April 14 carries a 90% chance of a light frost later that season, making it a high-risk gamble.

The median (50%) light-frost date is April 29 in spring and October 9 in fall; these dates mark even odds of a frost occurring later (spring) or earlier (fall) and are 162 days apart. A cautious spring plan would wait until the May 14 date, which has only a 10% chance of a frost later, while a cautious fall plan would aim for September 25, when there is only a 10% chance that a frost has arrived earlier. The 50% hard-frost dates are April 18 and October 20.

Hard frost at 28 °F can injure or kill plants that survive a light frost at 32 °F, so it represents a greater threat.

How to read the probabilities

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

  • Spring: "10% after May 14" 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 25" 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 Iowa City, IANumbered nearest stations: 1 — Cedar Rapids, IA — 22 mi; 2 — Washington, IA — 25 mi; 3 — Williamsburg, IA — 26 mi; 4 — Muscatine, IA — 26 mi; 5 — near Marion, IA — 31 mi.IL25 mi · 40 km1. Cedar Rapids, IA — 22 mi12. Washington, IA — 25 mi23. Williamsburg, IA — 26 mi34. Muscatine, IA — 26 mi45. near Marion, IA — 31 mi5
  1. Cedar Rapids, IA 22 mi (35 km)
  2. Washington, IA 25 mi (40 km)
  3. Williamsburg, IA 26 mi (41 km)
  4. Muscatine, IA 26 mi (42 km)
  5. near Marion, IA 31 mi (49 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: 41.6092, -91.505.