U.S. Frost Dates by Weather Station

NOAA station USC00137979 · Iowa

Frost Dates for Storm Lake, IA

NOAA weather station Storm Lake (USC00137979), Iowa · elevation 1442 ft (440 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 7only 1 spring in 10 still has a frost later
  • Typical last frostApril 2550% chance of a frost after it
  • Typical first fall frostOctober 1350% chance of a frost before it
  • Frost-free season170 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Storm Lake, IASpring: a frost after April 11 in 9 years out of 10, after April 25 in half of the years, after May 7 in 1 year out of 10. Fall: the first frost comes before October 1 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: 170 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 25First frost ~Oct 13Frost season at Storm Lake, IASpring: a frost after April 11 in 9 years out of 10, after April 25 in half of the years, after May 7 in 1 year out of 10. Fall: the first frost comes before October 1 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: 170 days.JFMAMJJASONDLast frost ~Apr 25First 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 26 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 7October 1
50% (typical)April 25October 13
90% (likely)April 11October 25
Frost-free season (32°F, 50% chance)
170 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 26 (1 day later than the 30-year normal), typical first fall frost October 16 (3 days later). Frost-free season 173 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 Storm Lake: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 7, 20% May 3, 30% May 1, 40% April 29, 50% April 25, 60% April 22, 70% April 19, 80% April 16, 90% April 11. Observed last spring frost in recent years: 2021 April 23, 2022 April 27, 2023 April 25, 2024 April 21, 2025 April 15, 2026 April 20.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 7Apr 25Apr 112021: April 232022: April 272023: April 252024: April 212025: April 152026: April 20Fall at Storm Lake: chance of a frost before this dateFall, chance of a frost before the date: 10% October 1, 20% October 4, 30% October 7, 40% October 10, 50% October 13, 60% October 16, 70% October 18, 80% October 21, 90% October 25. Observed first fall frost in recent years: 2021 October 23, 2022 October 15, 2023 October 27, 2024 October 16, 2025 October 23.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Oct 1Oct 13Oct 252021: October 232022: October 152023: October 272024: October 162025: 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
2021April 23October 23
2022April 27October 15
2023April 25October 27
2024April 21October 16
2025April 15October 23
2026April 20season not over yet

What these dates mean

The cautious fall date in Storm Lake for finishing the harvest is October 1, when there is only a 10 % chance that a light frost has arrived earlier. Waiting until this date lowers the risk to tender crops, while the later date of October 25 carries a 90 % chance that a frost is already present. These probabilities come from 26 years of NOAA normals (1991-2020).

In spring the cautious date for setting out tender crops is May 7, the 10 %-chance light-frost date; the 50 % spring date, April 25, represents an even-odds point for a light frost. The 50 % fall date, October 13, represents an even-odds point for a light frost, and the gamble dates are April 11 (90 % chance) and October 25 (90 % chance). The two 32°F 50% dates are 170 days apart, marking the span of equal odds for a light frost. Hard frost at 28 °F can damage plants that survive a 32 °F light frost, so the median hard-frost dates of April 15 and October 23 are especially important.

How to read the probabilities

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

  • Spring: "10% after May 7" 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 October 1" 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 Storm Lake, IANumbered nearest stations: 1 — Sioux Rapids, IA — 18 mi; 2 — Cherokee, IA — 19 mi; 3 — Sac City, IA — 19 mi; 4 — Pocahontas, IA — 28 mi; 5 — Rockwell City, IA — 34 mi.25 mi · 40 km1. Sioux Rapids, IA — 18 mi12. Cherokee, IA — 19 mi23. Sac City, IA — 19 mi34. Pocahontas, IA — 28 mi45. Rockwell City, IA — 34 mi5
  1. Sioux Rapids, IA 18 mi (29 km)
  2. Cherokee, IA 19 mi (31 km)
  3. Sac City, IA 19 mi (31 km)
  4. Pocahontas, IA 28 mi (44 km)
  5. Rockwell City, IA 34 mi (54 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: 42.6469, -95.1933.