U.S. Frost Dates by Weather Station

NOAA station USC00133718 · Iowa

Frost Dates for Hawarden, IA

NOAA weather station Hawarden (USC00133718), Iowa · elevation 1190 ft (363 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 14only 1 spring in 10 still has a frost later
  • Typical last frostMay 150% chance of a frost after it
  • Typical first fall frostOctober 450% chance of a frost before it
  • Frost-free season155 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Hawarden, IASpring: a frost after April 17 in 9 years out of 10, after May 1 in half of the years, after May 14 in 1 year out of 10. Fall: the first frost comes before September 21 in 1 year out of 10, before October 4 in half of the years, before October 18 in 9 years out of 10. Typical frost-free season: 155 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 1First frost ~Oct 4Frost season at Hawarden, IASpring: a frost after April 17 in 9 years out of 10, after May 1 in half of the years, after May 14 in 1 year out of 10. Fall: the first frost comes before September 21 in 1 year out of 10, before October 4 in half of the years, before October 18 in 9 years out of 10. Typical frost-free season: 155 days.JFMAMJJASONDLast frost ~May 1First frost ~Oct 4
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 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 14September 21
50% (typical)May 1October 4
90% (likely)April 17October 18
Frost-free season (32°F, 50% chance)
155 days
Hard frost (28°F), last in spring, 50% chance after
April 22
Hard frost (28°F), first in fall, 50% chance before
October 16

The last 15 years (2006–2020 normals)

Typical last frost May 2 (1 day later than the 30-year normal), typical first fall frost October 8 (4 days later). Frost-free season 158 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 Hawarden: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 14, 20% May 9, 30% May 6, 40% May 4, 50% May 1, 60% April 30, 70% April 26, 80% April 22, 90% April 17.Spring: last frostChance of a frost after this date10%50%90%May 1May 14May 1Apr 17Fall at Hawarden: chance of a frost before this dateFall, chance of a frost before the date: 10% September 21, 20% September 26, 30% September 29, 40% October 1, 50% October 4, 60% October 7, 70% October 10, 80% October 14, 90% October 18.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 21Oct 4Oct 18
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.

What these dates mean

May 14 is the cautious spring light-frost date, with only a 10% chance of a frost later, and it lets a gardener set out tender crops. The 50% light-frost dates, May 1 in spring and October 4 in fall, mark the median point where frost is as likely as not; they are not frost dates themselves. The cautious fall light-frost date is September 21, which carries a 10% chance of a frost earlier and signals when tender crops should be finished. The 50% hard-frost dates are April 22 for spring and October 16 for fall, indicating the median moment when temperatures reach 28 °F. A hard frost matters more than a light frost because 28 °F can damage or kill plants that would survive a 32 °F event.

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 21" 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 Hawarden, IANumbered nearest stations: 1 — Sioux Center, IA — 17 mi; 2 — Centerville, SD — 21 mi; 3 — Le Mars, IA — 23 mi; 4 — Vermillion, SD — 28 mi; 5 — Rock Rapids, IA — 34 mi.IASDNEMN25 mi · 40 km1. Sioux Center, IA — 17 mi12. Centerville, SD — 21 mi23. Le Mars, IA — 23 mi34. Vermillion, SD — 28 mi45. Rock Rapids, IA — 34 mi5
  1. Sioux Center, IA 17 mi (28 km)
  2. Centerville, SD 21 mi (34 km)
  3. Le Mars, IA 23 mi (37 km)
  4. Vermillion, SD 28 mi (44 km)
  5. Rock Rapids, 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: 43.0031, -96.485.