U.S. Frost Dates by Weather Station

NOAA station USC00136316 · Iowa

Frost Dates for Osceola, IA

NOAA weather station Osceola (USC00136316), Iowa · elevation 1028 ft (313 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 11only 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 Osceola, IASpring: a frost after April 13 in 9 years out of 10, after April 29 in half of the years, after May 11 in 1 year out of 10. Fall: the first frost comes before September 24 in 1 year out of 10, before October 9 in half of the years, before October 24 in 9 years out of 10. Typical frost-free season: 162 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 29First frost ~Oct 9Frost season at Osceola, IASpring: a frost after April 13 in 9 years out of 10, after April 29 in half of the years, after May 11 in 1 year out of 10. Fall: the first frost comes before September 24 in 1 year out of 10, before October 9 in half of the years, before October 24 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.Today

Frost dates (32°F)

Probability of frost, based on 26 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 11September 24
50% (typical)April 29October 9
90% (likely)April 13October 24
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 30 (1 day later than the 30-year normal), typical first fall frost October 12 (3 days later). Frost-free season 163 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 Osceola: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 11, 20% May 7, 30% May 3, 40% May 1, 50% April 29, 60% April 25, 70% April 22, 80% April 18, 90% April 13. Observed last spring frost in recent years: 2021 April 23, 2022 April 27, 2023 May 3, 2024 April 22.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 11Apr 29Apr 132021: April 232022: April 272023: May 32024: April 22Fall at Osceola: chance of a frost before this dateFall, chance of a frost before the date: 10% September 24, 20% September 29, 30% October 2, 40% October 6, 50% October 9, 60% October 12, 70% October 15, 80% October 19, 90% October 24. Observed first fall frost in recent years: 2021 October 22, 2022 October 8, 2023 October 10, 2024 October 16.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 24Oct 9Oct 242021: October 222022: October 82023: October 102024: October 16
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 23October 22
2022April 27October 8
2023May 3October 10
2024April 22October 16
2025incomplete recordno data
2026no dataseason not over yet

What these dates mean

May 11 is the cautious spring date in Osceola; with only a 10 % chance of a light frost after that day, a gardener can plan to set out tender crops with low risk. The counterpart in fall is September 24, the cautious date for finishing the harvest of tender crops because only a 10 % chance exists that a light frost has already arrived.

The median light-frost dates are April 29 in spring and October 9 in fall; each represents an even-odds point for a frost occurring later (spring) or earlier (fall). The 50 % hard-frost dates are April 18 and October 20; a hard frost at 28 °F can damage plants that survive a light frost, making it a more critical threshold. The two 32 °F 50 % dates are 162 days apart, giving a long period between the even-odds points for light frost.

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 24" 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 Osceola, IANumbered nearest stations: 1 — Beaconsfield, IA — 21 mi; 2 — Indianola, IA — 25 mi; 3 — Chariton, IA — 25 mi; 4 — Lamoni, IA — 29 mi; 5 — Creston, IA — 34 mi.IAMO25 mi · 40 km1. Beaconsfield, IA — 21 mi12. Indianola, IA — 25 mi23. Chariton, IA — 25 mi34. Lamoni, IA — 29 mi45. Creston, IA — 34 mi5
  1. Beaconsfield, IA 21 mi (34 km)
  2. Indianola, IA 25 mi (40 km)
  3. Chariton, IA 25 mi (40 km)
  4. Lamoni, IA 29 mi (47 km)
  5. Creston, IA 34 mi (54 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: 41.0194, -93.7503.