U.S. Frost Dates by Weather Station

NOAA station USC00137161 · Iowa

Frost Dates for Rockwell City, IA

NOAA weather station Rockwell City (USC00137161), Iowa · elevation 1214 ft (370 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 6only 1 spring in 10 still has a frost later
  • Typical last frostApril 2650% chance of a frost after it
  • Typical first fall frostOctober 1050% chance of a frost before it
  • Frost-free season167 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Rockwell City, IASpring: a frost after April 11 in 9 years out of 10, after April 26 in half of the years, after May 6 in 1 year out of 10. Fall: the first frost comes before September 27 in 1 year out of 10, before October 10 in half of the years, before October 24 in 9 years out of 10. Typical frost-free season: 167 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 26First frost ~Oct 10Frost season at Rockwell City, IASpring: a frost after April 11 in 9 years out of 10, after April 26 in half of the years, after May 6 in 1 year out of 10. Fall: the first frost comes before September 27 in 1 year out of 10, before October 10 in half of the years, before October 24 in 9 years out of 10. Typical frost-free season: 167 days.JFMAMJJASONDLast frost ~Apr 26First frost ~Oct 10
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 6September 27
50% (typical)April 26October 10
90% (likely)April 11October 24
Frost-free season (32°F, 50% chance)
167 days
Hard frost (28°F), last in spring, 50% chance after
April 16
Hard frost (28°F), first in fall, 50% chance before
October 21

The last 15 years (2006–2020 normals)

Typical last frost April 25 (1 day earlier than the 30-year normal), typical first fall frost October 17 (7 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 Rockwell City: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 6, 20% May 3, 30% May 1, 40% April 29, 50% April 26, 60% April 23, 70% April 21, 80% April 17, 90% April 11. Observed last spring frost in recent years: 2021 April 23, 2022 April 27, 2023 April 26.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 6Apr 26Apr 112021: April 232022: April 272023: April 26Fall at Rockwell City: chance of a frost before this dateFall, chance of a frost before the date: 10% September 27, 20% October 1, 30% October 4, 40% October 7, 50% October 10, 60% October 13, 70% October 16, 80% October 19, 90% October 24. Observed first fall frost in recent years: 2021 October 22, 2022 September 28, 2023 October 10.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 27Oct 10Oct 242021: October 222022: September 282023: October 10
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 27September 28
2023April 26October 10
2024incomplete recordno data
2025incomplete recordincomplete record
2026incomplete recordseason not over yet

What these dates mean

The 167 days between the 32°F 50% dates in Rockwell City – April 26 in spring and October 10 in fall – frame the period when a light frost has an even 50 % chance of occurring either later (spring) or earlier (fall). Gardeners view these median dates as the central window for planning, while the hard-frost 28°F 50% dates, April 16 and October 21, mark the midpoint of more severe freezing risk.

For a cautious approach, the spring light-frost date with only a 10 % chance of a later frost is May 6, the point at which tender crops can be set out with low risk. In the autumn, the cautious date with only a 10 % chance of an earlier frost is September 27, after which finishing tender harvests becomes safer. A hard frost matters more because temperatures at 28 °F can damage plant tissue that survives the milder 32 °F 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 6" 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 27" 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 Rockwell City, IANumbered nearest stations: 1 — Sac City, IA — 18 mi; 2 — Pocahontas, IA — 23 mi; 3 — Fort Dodge, IA — 25 mi; 4 — Carroll, IA — 26 mi; 5 — Jefferson, IA — 29 mi.NE25 mi · 40 km1. Sac City, IA — 18 mi12. Pocahontas, IA — 23 mi23. Fort Dodge, IA — 25 mi34. Carroll, IA — 26 mi45. Jefferson, IA — 29 mi5
  1. Sac City, IA 18 mi (29 km)
  2. Pocahontas, IA 23 mi (37 km)
  3. Fort Dodge, IA 25 mi (41 km)
  4. Carroll, IA 26 mi (41 km)
  5. Jefferson, IA 29 mi (47 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: 42.3969, -94.6292.