U.S. Frost Dates by Weather Station

NOAA station USC00137700 · Iowa

Frost Dates for Sioux Center, IA

NOAA weather station Sioux Center 2 SE (USC00137700), Iowa · elevation 1360 ft (415 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 12only 1 spring in 10 still has a frost later
  • Typical last frostApril 3050% chance of a frost after it
  • Typical first fall frostOctober 350% chance of a frost before it
  • Frost-free season154 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Sioux Center, IASpring: a frost after April 17 in 9 years out of 10, after April 30 in half of the years, after May 12 in 1 year out of 10. Fall: the first frost comes before September 19 in 1 year out of 10, before October 3 in half of the years, before October 18 in 9 years out of 10. Typical frost-free season: 154 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 30First frost ~Oct 3Frost season at Sioux Center, IASpring: a frost after April 17 in 9 years out of 10, after April 30 in half of the years, after May 12 in 1 year out of 10. Fall: the first frost comes before September 19 in 1 year out of 10, before October 3 in half of the years, before October 18 in 9 years out of 10. Typical frost-free season: 154 days.JFMAMJJASONDLast frost ~Apr 30First frost ~Oct 3
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 30 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 12September 19
50% (typical)April 30October 3
90% (likely)April 17October 18
Frost-free season (32°F, 50% chance)
154 days
Hard frost (28°F), last in spring, 50% chance after
April 21
Hard frost (28°F), first in fall, 50% chance before
October 14

The last 15 years (2006–2020 normals)

Typical last frost April 30 (same as the 30-year normal), typical first fall frost October 6 (3 days later). Frost-free season 157 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 Sioux Center: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 12, 20% May 8, 30% May 5, 40% May 2, 50% April 30, 60% April 28, 70% April 25, 80% April 22, 90% April 17. Observed last spring frost in recent years: 2021 May 11, 2022 May 4, 2023 May 3, 2024 April 21, 2025 April 19, 2026 May 6.Spring: last frostChance of a frost after this date10%50%90%May 1May 12Apr 30Apr 172021: May 112022: May 42023: May 32024: April 212025: April 192026: May 6Fall at Sioux Center: chance of a frost before this dateFall, chance of a frost before the date: 10% September 19, 20% September 24, 30% September 28, 40% October 1, 50% October 3, 60% October 5, 70% October 9, 80% October 13, 90% October 18. Observed first fall frost in recent years: 2021 October 22, 2022 September 28, 2023 October 10, 2024 October 14, 2025 October 22.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 19Oct 3Oct 182021: October 222022: September 282023: October 102024: October 142025: 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 11October 22
2022May 4September 28
2023May 3October 10
2024April 21October 14
2025April 19October 22
2026May 6season not over yet

What these dates mean

May 12 is the cautious spring light-frost date for Sioux Center; with only a 10 % chance of a frost later than that day, a gardener can plan to set out tender crops with minimal risk. The 50 % spring date is April 30, which marks an even chance of a frost occurring later, while the 50 % fall date is October 3, indicating an even chance of a frost occurring earlier. September 19 is the cautious fall light-frost date, carrying a 10 % chance that a frost has arrived earlier, so it is the date to finish harvesting tender crops. The hard-frost median dates are April 21 in spring and October 14 in fall. A hard frost at 28 °F can damage plant tissue that survives a light frost at 32 °F. The record spans 30 years and the interval between the two 32 °F 50 % dates is 154 days.

How to read the probabilities

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

  • Spring: "10% after May 12" 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 19" 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 Sioux Center, IANumbered nearest stations: 1 — Hawarden, IA — 17 mi; 2 — Sheldon, IA — 17 mi; 3 — Le Mars, IA — 19 mi; 4 — Rock Rapids, IA — 26 mi; 5 — Sanborn, IA — 26 mi.IASDMNNE25 mi · 40 km1. Hawarden, IA — 17 mi12. Sheldon, IA — 17 mi23. Le Mars, IA — 19 mi34. Rock Rapids, IA — 26 mi45. Sanborn, IA — 26 mi5
  1. Hawarden, IA 17 mi (28 km)
  2. Sheldon, IA 17 mi (28 km)
  3. Le Mars, IA 19 mi (30 km)
  4. Rock Rapids, IA 26 mi (42 km)
  5. Sanborn, IA 26 mi (42 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: 43.0558, -96.1525.