U.S. Frost Dates by Weather Station

NOAA station USC00131319 · Iowa

Frost Dates near Marion, IA

NOAA weather station Cedar Rapids #1 (USC00131319), Iowa · elevation 813 ft (248 m) · hardiness zone 5b*

Marion is the nearest town to the station (1.2 mi away) in GeoNames (CC BY 4.0). The dates below are measured at the station, not in the town itself.

  • Lower-risk planting dateafter May 13only 1 spring in 10 still has a frost later
  • Typical last frostApril 2850% chance of a frost after it
  • Typical first fall frostOctober 1250% chance of a frost before it
  • Frost-free season166 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season near Marion, IASpring: a frost after April 14 in 9 years out of 10, after April 28 in half of the years, after May 13 in 1 year out of 10. Fall: the first frost comes before September 29 in 1 year out of 10, before October 12 in half of the years, before October 25 in 9 years out of 10. Typical frost-free season: 166 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 28First frost ~Oct 12Frost season near Marion, IASpring: a frost after April 14 in 9 years out of 10, after April 28 in half of the years, after May 13 in 1 year out of 10. Fall: the first frost comes before September 29 in 1 year out of 10, before October 12 in half of the years, before October 25 in 9 years out of 10. Typical frost-free season: 166 days.JFMAMJJASONDLast frost ~Apr 28First frost ~Oct 12
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 30 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 13September 29
50% (typical)April 28October 12
90% (likely)April 14October 25
Frost-free season (32°F, 50% chance)
166 days
Hard frost (28°F), last in spring, 50% chance after
April 17
Hard frost (28°F), first in fall, 50% chance before
October 22

The last 15 years (2006–2020 normals)

Typical last frost April 29 (1 day later than the 30-year normal), typical first fall frost October 14 (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 near Marion: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 13, 20% May 8, 30% May 4, 40% May 1, 50% April 28, 60% April 25, 70% April 22, 80% April 18, 90% April 14. Observed last spring frost in recent years: 2021 May 12, 2022 April 26, 2023 May 3, 2024 April 21, 2025 April 16, 2026 May 7.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 13Apr 28Apr 142021: May 122022: April 262023: May 32024: April 212025: April 162026: May 7Fall near Marion: chance of a frost before this dateFall, chance of a frost before the date: 10% September 29, 20% October 3, 30% October 7, 40% October 9, 50% October 12, 60% October 15, 70% October 17, 80% October 20, 90% October 25. Observed first fall frost in recent years: 2021 October 23, 2022 October 8, 2023 October 10, 2024 October 15, 2025 October 23.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 29Oct 12Oct 252021: October 232022: October 82023: 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 12October 23
2022April 26October 8
2023May 3October 10
2024April 21October 15
2025April 16October 23
2026May 7season not over yet

What these dates mean

Setting out tender crops on the early spring date, April 14, carries a 90 % chance of a frost later, so the risk is high for the Marion area.

The cautious spring date for tender crops is May 13, when only a 10 % chance of a later frost remains. The 50 % date is April 28; at that point a frost is equally likely to occur later or not, giving gardeners a clear midpoint of the light-frost probability curve. In the fall, the cautious date to finish harvesting tender crops is September 29, with a 10 % chance that a frost has already arrived, while the 50 % date is October 12, marking the even-odds point for an earlier frost.

The 50 % hard-frost dates are April 17 in spring and October 22 in fall; a hard frost can kill plant tissue that would survive a light frost, making it the more damaging temperature threshold.

How to read the probabilities

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

  • Spring: "10% after May 13" 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 29" 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 Marion, IANumbered nearest stations: 1 — Cedar Rapids, IA — 13 mi; 2 — Vinton, IA — 23 mi; 3 — near Manchester, IA — 30 mi; 4 — Iowa City, IA — 31 mi; 5 — Williamsburg, IA — 34 mi.ILWI25 mi · 40 km1. Cedar Rapids, IA — 13 mi12. Vinton, IA — 23 mi23. near Manchester, IA — 30 mi34. Iowa City, IA — 31 mi45. Williamsburg, IA — 34 mi5
  1. Cedar Rapids, IA 13 mi (21 km)
  2. Vinton, IA 23 mi (37 km)
  3. near Manchester, IA 30 mi (48 km)
  4. Iowa City, IA 31 mi (49 km)
  5. Williamsburg, IA 34 mi (55 km)

Sources

* Hardiness zone 5b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 42.0497, -91.5881.