U.S. Frost Dates by Weather Station

NOAA station USC00130157 · Iowa

Frost Dates for Allison, IA

NOAA weather station Allison (USC00130157), Iowa · elevation 1038 ft (316 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 8only 1 spring in 10 still has a frost later
  • Typical last frostApril 2750% chance of a frost after it
  • Typical first fall frostOctober 850% chance of a frost before it
  • Frost-free season165 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Allison, IASpring: a frost after April 12 in 9 years out of 10, after April 27 in half of the years, after May 8 in 1 year out of 10. Fall: the first frost comes before September 24 in 1 year out of 10, before October 8 in half of the years, before October 22 in 9 years out of 10. Typical frost-free season: 165 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 27First frost ~Oct 8Frost season at Allison, IASpring: a frost after April 12 in 9 years out of 10, after April 27 in half of the years, after May 8 in 1 year out of 10. Fall: the first frost comes before September 24 in 1 year out of 10, before October 8 in half of the years, before October 22 in 9 years out of 10. Typical frost-free season: 165 days.JFMAMJJASONDLast frost ~Apr 27First frost ~Oct 8
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 8September 24
50% (typical)April 27October 8
90% (likely)April 12October 22
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 15 (7 days later). Frost-free season 169 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 Allison: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 8, 20% May 5, 30% May 2, 40% April 30, 50% April 27, 60% April 24, 70% April 21, 80% April 17, 90% April 12. Observed last spring frost in recent years: 2021 April 26, 2022 April 27, 2023 May 2, 2024 April 21, 2026 May 7.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 8Apr 27Apr 122021: April 262022: April 272023: May 22024: April 212026: May 7Fall at Allison: chance of a frost before this dateFall, chance of a frost before the date: 10% September 24, 20% September 29, 30% October 2, 40% October 5, 50% October 8, 60% October 11, 70% October 14, 80% October 18, 90% October 22. Observed first fall frost in recent years: 2021 October 22, 2022 October 8, 2023 October 10, 2024 October 15.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 24Oct 8Oct 222021: October 222022: October 82023: October 102024: October 15
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 26October 22
2022April 27October 8
2023May 2October 10
2024April 21October 15
2025incomplete recordincomplete record
2026May 7season not over yet

What these dates mean

May 8 is the cautious spring date in Allison, providing only a 10% chance of a light frost later and allowing a gardener to set out tender crops with minimal risk. April 27 is the 50% date, a point where there is a 50% chance of a light frost later in the season, while October 8 is the 50% date, a point where there is a 50% chance of a light frost earlier in the season. September 24 is the cautious fall date, carrying a 10% chance that a light frost has already arrived, giving a gardener a reliable deadline to finish harvesting tender crops. Hard frost at 28°F can damage or kill plants more severely than a light frost at 32°F, so the April 16 and October 20 50% hard-frost dates are especially important for gardeners.

How to read the probabilities

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

  • Spring: "10% after May 8" 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 24" 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 Allison, IANumbered nearest stations: 1 — Hampton, IA — 20 mi; 2 — Charles City, IA — 22 mi; 3 — Waterloo, IA — 25 mi; 4 — Grundy Center, IA — 27 mi; 5 — Tripoli, IA — 28 mi.MNWI25 mi · 40 km1. Hampton, IA — 20 mi12. Charles City, IA — 22 mi23. Waterloo, IA — 25 mi34. Grundy Center, IA — 27 mi45. Tripoli, IA — 28 mi5
  1. Hampton, IA 20 mi (33 km)
  2. Charles City, IA 22 mi (36 km)
  3. Waterloo, IA 25 mi (40 km)
  4. Grundy Center, IA 27 mi (43 km)
  5. Tripoli, IA 28 mi (45 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: 42.7536, -92.8022.