U.S. Frost Dates by Weather Station

NOAA station USW00014943 · Iowa

Frost Dates near Sioux City, IA

NOAA weather station Sioux City Gateway Airport (USW00014943), Iowa · elevation 1095 ft (334 m) · hardiness zone 5a*

Sioux City is the nearest town to the station (7.6 mi away) in GeoNames (CC BY 4.0). The dates below are measured at the station, not in the town itself.

  • 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 550% chance of a frost before it
  • Frost-free season159 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season near Sioux City, IASpring: a frost after April 16 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 22 in 1 year out of 10, before October 5 in half of the years, before October 18 in 9 years out of 10. Typical frost-free season: 159 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 29First frost ~Oct 5Frost season near Sioux City, IASpring: a frost after April 16 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 22 in 1 year out of 10, before October 5 in half of the years, before October 18 in 9 years out of 10. Typical frost-free season: 159 days.JFMAMJJASONDLast frost ~Apr 29First frost ~Oct 5
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 22
50% (typical)April 29October 5
90% (likely)April 16October 18
Frost-free season (32°F, 50% chance)
159 days
Hard frost (28°F), last in spring, 50% chance after
April 20
Hard frost (28°F), first in fall, 50% chance before
October 15

The last 15 years (2006–2020 normals)

Typical last frost April 29 (same as the 30-year normal), typical first fall frost October 7 (2 days later). Frost-free season 161 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 near Sioux City: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 14, 20% May 8, 30% May 4, 40% May 1, 50% April 29, 60% April 27, 70% April 24, 80% April 21, 90% April 16. Observed last spring frost in recent years: 2021 May 11, 2022 May 22, 2023 May 3, 2024 April 24, 2025 May 3, 2026 May 6.Spring: last frostChance of a frost after this date10%50%90%May 1May 14Apr 29Apr 162021: May 112022: May 222023: May 32024: April 242025: May 32026: May 6Fall near Sioux City: chance of a frost before this dateFall, chance of a frost before the date: 10% September 22, 20% September 26, 30% September 29, 40% October 2, 50% October 5, 60% October 8, 70% October 11, 80% October 14, 90% October 18. Observed first fall frost in recent years: 2021 October 21, 2022 October 7, 2023 October 7, 2024 October 7, 2025 October 21.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 22Oct 5Oct 182021: October 212022: October 72023: October 72024: October 72025: October 21
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 21
2022May 22October 7
2023May 3October 7
2024April 24October 7
2025May 3October 21
2026May 6season not over yet

What these dates mean

The 159-day span between the 32°F 50% dates, April 29 and October 5, marks the interval when light frosts are equally likely to have occurred or not, and it encloses the typical growing season for tender crops in the Sioux City area. During this window gardeners can expect a roughly even chance of a light frost either side of those dates, while the record covers 29 years.

For a low-risk schedule, the cautious spring date is May 14, when there is only a 10 % chance of a light frost later, making it the preferred day to set out tender crops. In the fall, the cautious date is September 22, with only a 10 % chance that a light frost has arrived earlier, signaling when tender crops should be finished. A hard frost, recorded at 28 °F, is more damaging than a light frost; its 50 % dates are April 20 in spring and October 15 in fall, and a 28 °F event can kill plants that survive a 32 °F 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 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 22" 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 City, IANumbered nearest stations: 1 — Wakefield, NE — 26 mi; 2 — Le Mars, IA — 29 mi; 3 — Wayne, NE — 34 mi; 4 — near Mapleton, IA — 34 mi; 5 — Castana Experiment Farm, IA — 36 mi.IASD25 mi · 40 km1. Wakefield, NE — 26 mi12. Le Mars, IA — 29 mi23. Wayne, NE — 34 mi34. near Mapleton, IA — 34 mi45. Castana Experiment Farm, IA — 36 mi5
  1. Wakefield, NE 26 mi (42 km)
  2. Le Mars, IA 29 mi (47 km)
  3. Wayne, NE 34 mi (55 km)
  4. near Mapleton, IA 34 mi (55 km)
  5. Castana Experiment Farm, IA 36 mi (58 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: 42.3914, -96.3792.