U.S. Frost Dates by Weather Station

NOAA station USC00137312 · Iowa

Frost Dates for Sac City, IA

NOAA weather station Sac City (USC00137312), Iowa · elevation 1210 ft (369 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 11only 1 spring in 10 still has a frost later
  • Typical last frostApril 3050% chance of a frost after it
  • Typical first fall frostOctober 650% chance of a frost before it
  • Frost-free season158 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Sac City, IASpring: a frost after April 15 in 9 years out of 10, after April 30 in half of the years, after May 11 in 1 year out of 10. Fall: the first frost comes before September 23 in 1 year out of 10, before October 6 in half of the years, before October 20 in 9 years out of 10. Typical frost-free season: 158 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 30First frost ~Oct 6Frost season at Sac City, IASpring: a frost after April 15 in 9 years out of 10, after April 30 in half of the years, after May 11 in 1 year out of 10. Fall: the first frost comes before September 23 in 1 year out of 10, before October 6 in half of the years, before October 20 in 9 years out of 10. Typical frost-free season: 158 days.JFMAMJJASONDLast frost ~Apr 30First frost ~Oct 6
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 11September 23
50% (typical)April 30October 6
90% (likely)April 15October 20
Frost-free season (32°F, 50% chance)
158 days
Hard frost (28°F), last in spring, 50% chance after
April 19
Hard frost (28°F), first in fall, 50% chance before
October 17

The last 15 years (2006–2020 normals)

Typical last frost April 30 (same as the 30-year normal), typical first fall frost October 10 (4 days later). Frost-free season 164 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 Sac City: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 11, 20% May 7, 30% May 4, 40% May 2, 50% April 30, 60% April 28, 70% April 24, 80% April 20, 90% April 15. Observed last spring frost in recent years: 2021 May 11, 2022 May 4, 2023 April 27, 2024 April 21, 2025 April 9.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 11Apr 30Apr 152021: May 112022: May 42023: April 272024: April 212025: April 9Fall at Sac City: chance of a frost before this dateFall, chance of a frost before the date: 10% September 23, 20% September 28, 30% October 1, 40% October 4, 50% October 6, 60% October 10, 70% October 12, 80% October 16, 90% October 20. Observed first fall frost in recent years: 2021 October 22, 2022 September 28, 2024 October 15, 2025 October 23.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 23Oct 6Oct 202021: October 222022: September 282024: October 152025: 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
2021May 11October 22
2022May 4September 28
2023April 27incomplete record
2024April 21October 15
2025April 9October 23
2026incomplete recordseason not over yet

What these dates mean

May 11 marks the cautious spring date for light frost (32 °F) in Sac City, Iowa; with only a 10 % chance of a frost later, a gardener can plan to set out tender crops after this day.

The 50 % date of April 30 indicates the point at which a light frost is equally likely to have occurred or not, while the hard-frost 50 % date of April 19 shows the same balance for a 28 °F event. Both dates give a gardener a reference for when the risk of frost is balanced.

In the fall the cautious date is September 23, when there is only a 10 % chance that a light frost has already arrived, permitting the final harvest of tender crops. A hard frost at 28 °F, such as the median date of October 17, can cause far greater damage to plants 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 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 23" 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 Sac City, IANumbered nearest stations: 1 — Rockwell City, IA — 18 mi; 2 — Storm Lake, IA — 19 mi; 3 — Carroll, IA — 25 mi; 4 — Pocahontas, IA — 27 mi; 5 — Denison, IA — 32 mi.NESD25 mi · 40 km1. Rockwell City, IA — 18 mi12. Storm Lake, IA — 19 mi23. Carroll, IA — 25 mi34. Pocahontas, IA — 27 mi45. Denison, IA — 32 mi5
  1. Rockwell City, IA 18 mi (29 km)
  2. Storm Lake, IA 19 mi (31 km)
  3. Carroll, IA 25 mi (41 km)
  4. Pocahontas, IA 27 mi (43 km)
  5. Denison, IA 32 mi (52 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: 42.4194, -94.9761.