U.S. Frost Dates by Weather Station

NOAA station USC00136940 · Iowa

Frost Dates for Red Oak, IA

NOAA weather station Red Oak (USC00136940), Iowa · elevation 1040 ft (317 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 8only 1 spring in 10 still has a frost later
  • Typical last frostApril 2450% 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 Red Oak, IASpring: a frost after April 10 in 9 years out of 10, after April 24 in half of the years, after May 8 in 1 year out of 10. Fall: the first frost comes before September 26 in 1 year out of 10, before October 13 in half of the years, before October 25 in 9 years out of 10. Typical frost-free season: 169 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 24First frost ~Oct 13Frost season at Red Oak, IASpring: a frost after April 10 in 9 years out of 10, after April 24 in half of the years, after May 8 in 1 year out of 10. Fall: the first frost comes before September 26 in 1 year out of 10, before October 13 in half of the years, before October 25 in 9 years out of 10. Typical frost-free season: 169 days.JFMAMJJASONDLast frost ~Apr 24First 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 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 8September 26
50% (typical)April 24October 13
90% (likely)April 10October 25
Frost-free season (32°F, 50% chance)
169 days
Hard frost (28°F), last in spring, 50% chance after
April 15
Hard frost (28°F), first in fall, 50% chance before
October 23

The last 15 years (2006–2020 normals)

Typical last frost April 24 (same as the 30-year normal), typical first fall frost October 17 (4 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 Red Oak: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 8, 20% May 3, 30% April 30, 40% April 28, 50% April 24, 60% April 21, 70% April 18, 80% April 15, 90% April 10. Observed last spring frost in recent years: 2021 May 5, 2022 April 27, 2023 May 3, 2024 April 21, 2025 April 8.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 8Apr 24Apr 102021: May 52022: April 272023: May 32024: April 212025: April 8Fall at Red Oak: chance of a frost before this dateFall, chance of a frost before the date: 10% September 26, 20% October 1, 30% October 6, 40% October 10, 50% October 13, 60% October 16, 70% October 19, 80% October 22, 90% October 25. Observed first fall frost in recent years: 2021 October 22, 2022 October 8, 2023 October 16, 2024 October 15, 2025 October 22.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 26Oct 13Oct 252021: October 222022: October 82023: October 162024: October 152025: 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 5October 22
2022April 27October 8
2023May 3October 16
2024April 21October 15
2025April 8October 22
2026incomplete recordseason not over yet

What these dates mean

Setting out tender crops on April 10 carries a 90% chance of a light frost later that season in Red Oak, making it a gamble for a spring planting. Such a high probability means seedlings are likely to be exposed to freezing temperatures.

A cautious spring plan would wait until the May 8 date, which has only a 10% chance of a light frost later. The 50% spring date is April 24, when the odds of a light frost later are equal. For the fall, the careful date to finish harvesting tender crops is September 26, with a 10% chance of a light frost earlier, while October 13 serves as the 50% date, giving an even chance of a light frost earlier.

Hard-frost thresholds (28 °F) are noted on April 15 and October 23; a hard frost can damage plants more severely than 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 8" 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 26" 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 Red Oak, IANumbered nearest stations: 1 — Shenandoah, IA — 17 mi; 2 — Oakland, IA — 22 mi; 3 — Clarinda, IA — 23 mi; 4 — Sidney, IA — 28 mi; 5 — Atlantic, IA — 31 mi.IANEMO25 mi · 40 km1. Shenandoah, IA — 17 mi12. Oakland, IA — 22 mi23. Clarinda, IA — 23 mi34. Sidney, IA — 28 mi45. Atlantic, IA — 31 mi5
  1. Shenandoah, IA 17 mi (28 km)
  2. Oakland, IA 22 mi (36 km)
  3. Clarinda, IA 23 mi (36 km)
  4. Sidney, IA 28 mi (45 km)
  5. Atlantic, IA 31 mi (50 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: 41.0036, -95.2419.