U.S. Frost Dates by Weather Station

NOAA station USC00137594 · Iowa

Frost Dates for Sheldon, IA

NOAA weather station Sheldon (USC00137594), Iowa · elevation 1420 ft (433 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 18only 1 spring in 10 still has a frost later
  • Typical last frostMay 550% chance of a frost after it
  • Typical first fall frostSeptember 2850% chance of a frost before it
  • Frost-free season145 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Sheldon, IASpring: a frost after April 24 in 9 years out of 10, after May 5 in half of the years, after May 18 in 1 year out of 10. Fall: the first frost comes before September 14 in 1 year out of 10, before September 28 in half of the years, before October 12 in 9 years out of 10. Typical frost-free season: 145 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 5First frost ~Sep 28Frost season at Sheldon, IASpring: a frost after April 24 in 9 years out of 10, after May 5 in half of the years, after May 18 in 1 year out of 10. Fall: the first frost comes before September 14 in 1 year out of 10, before September 28 in half of the years, before October 12 in 9 years out of 10. Typical frost-free season: 145 days.JFMAMJJASONDLast frost ~May 5First frost ~Sep 28
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 18September 14
50% (typical)May 5September 28
90% (likely)April 24October 12
Frost-free season (32°F, 50% chance)
145 days
Hard frost (28°F), last in spring, 50% chance after
April 28
Hard frost (28°F), first in fall, 50% chance before
October 6

The last 15 years (2006–2020 normals)

Typical last frost May 5 (same as the 30-year normal), typical first fall frost October 3 (5 days later). Frost-free season 149 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 Sheldon: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 18, 20% May 13, 30% May 9, 40% May 7, 50% May 5, 60% May 3, 70% May 1, 80% April 28, 90% April 24.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 18May 5Apr 24Fall at Sheldon: chance of a frost before this dateFall, chance of a frost before the date: 10% September 14, 20% September 19, 30% September 23, 40% September 26, 50% September 28, 60% October 1, 70% October 3, 80% October 7, 90% October 12.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 14Sep 28Oct 12
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

Setting out tender crops on April 24 in Sheldon carries a 90 % chance that a light frost will still occur, so planting that early is a gamble for the season.

The 50 % spring light-frost date is May 5, marking the point at which a gardener faces an even chance of a frost later, while the cautious spring date is May 18, when only a 10 % chance of a later frost remains. In fall, the 50 % light-frost date is September 28, and the cautious date to finish harvesting tender crops is September 14, when there is just a 10 % chance a frost has already arrived; October 12 would be a gamble with a 90 % chance of an earlier frost.

A hard frost, recorded at 28 °F, is more damaging than a light frost at 32 °F because it can kill plant tissue that would otherwise survive milder freezing.

How to read the probabilities

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

  • Spring: "10% after May 18" 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 14" 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 Sheldon, IANumbered nearest stations: 1 — Sanborn, IA — 10 mi; 2 — Primghar, IA — 13 mi; 3 — Sibley, IA — 16 mi; 4 — Sioux Center, IA — 17 mi; 5 — Rock Rapids, IA — 23 mi.SDMN25 mi · 40 km1. Sanborn, IA — 10 mi12. Primghar, IA — 13 mi23. Sibley, IA — 16 mi34. Sioux Center, IA — 17 mi45. Rock Rapids, IA — 23 mi5
  1. Sanborn, IA 10 mi (16 km)
  2. Primghar, IA 13 mi (21 km)
  3. Sibley, IA 16 mi (26 km)
  4. Sioux Center, IA 17 mi (28 km)
  5. Rock Rapids, IA 23 mi (38 km)

Sources

* Hardiness zone 4b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 43.1803, -95.8533.