U.S. Frost Dates by Weather Station

NOAA station USW00094910 · Iowa

Frost Dates for Waterloo, IA

NOAA weather station Waterloo Municipal Airport (USW00094910), Iowa · elevation 868 ft (265 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 10only 1 spring in 10 still has a frost later
  • Typical last frostApril 2750% chance of a frost after it
  • Typical first fall frostOctober 1050% chance of a frost before it
  • Frost-free season165 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Waterloo, IASpring: a frost after April 11 in 9 years out of 10, after April 27 in half of the years, after May 10 in 1 year out of 10. Fall: the first frost comes before September 26 in 1 year out of 10, before October 10 in half of the years, before October 21 in 9 years out of 10. Typical frost-free season: 165 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 27First frost ~Oct 10Frost season at Waterloo, IASpring: a frost after April 11 in 9 years out of 10, after April 27 in half of the years, after May 10 in 1 year out of 10. Fall: the first frost comes before September 26 in 1 year out of 10, before October 10 in half of the years, before October 21 in 9 years out of 10. Typical frost-free season: 165 days.JFMAMJJASONDLast frost ~Apr 27First 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 30 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 10September 26
50% (typical)April 27October 10
90% (likely)April 11October 21
Frost-free season (32°F, 50% chance)
165 days
Hard frost (28°F), last in spring, 50% chance after
April 16
Hard frost (28°F), first in fall, 50% chance before
October 20

The last 15 years (2006–2020 normals)

Typical last frost April 28 (1 day later than the 30-year normal), typical first fall frost October 12 (2 days later). Frost-free season 167 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 Waterloo: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 10, 20% May 5, 30% May 2, 40% April 30, 50% April 27, 60% April 24, 70% April 20, 80% April 16, 90% April 11. Observed last spring frost in recent years: 2021 May 8, 2022 May 4, 2023 May 3, 2024 April 21, 2025 April 16, 2026 May 11.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 10Apr 27Apr 112021: May 82022: May 42023: May 32024: April 212025: April 162026: May 11Fall at Waterloo: chance of a frost before this dateFall, chance of a frost before the date: 10% September 26, 20% October 1, 30% October 4, 40% October 7, 50% October 10, 60% October 12, 70% October 15, 80% October 18, 90% October 21. Observed first fall frost in recent years: 2021 October 22, 2022 September 28, 2023 October 10, 2024 October 15, 2025 October 23.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 26Oct 10Oct 212021: October 222022: September 282023: October 102024: October 152025: 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
2021May 8October 22
2022May 4September 28
2023May 3October 10
2024April 21October 15
2025April 16October 23
2026May 11season not over yet

What these dates mean

September 26 is the cautious date to finish harvesting tender crops in Waterloo, as there is only a 10% chance that a light frost has arrived earlier. The 50% date is October 10, marking even odds for a light frost in the fall, while October 21 carries a 90% chance and would be a gamble for late tender crops.

In spring the cautious date for setting out tender crops is May 10, with a 10% chance of a frost later than that day; the 50% date is April 27, and April 11 carries a 90% chance making it risky. Hard-frost thresholds are noted on April 16 and October 20; a hard frost at 28 °F can damage plants more severely than a light frost at 32 °F, so those dates are important for gardeners.

The record spans 30 years and the span between the two 32 °F 50% dates is 165 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 10" 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 26" 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 Waterloo, IANumbered nearest stations: 1 — Tripoli, IA — 19 mi; 2 — Grundy Center, IA — 22 mi; 3 — Allison, IA — 25 mi; 4 — Vinton, IA — 33 mi; 5 — New Hampton, IA — 34 mi.WI25 mi · 40 km1. Tripoli, IA — 19 mi12. Grundy Center, IA — 22 mi23. Allison, IA — 25 mi34. Vinton, IA — 33 mi45. New Hampton, IA — 34 mi5
  1. Tripoli, IA 19 mi (31 km)
  2. Grundy Center, IA 22 mi (36 km)
  3. Allison, IA 25 mi (40 km)
  4. Vinton, IA 33 mi (54 km)
  5. New Hampton, IA 34 mi (55 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: 42.5544, -92.4011.