U.S. Frost Dates by Weather Station

NOAA station USC00137386 · Iowa

Frost Dates for Sanborn, IA

NOAA weather station Sanborn (USC00137386), Iowa · elevation 1551 ft (473 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 13only 1 spring in 10 still has a frost later
  • Typical last frostMay 150% chance of a frost after it
  • Typical first fall frostOctober 750% chance of a frost before it
  • Frost-free season160 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Sanborn, IASpring: a frost after April 16 in 9 years out of 10, after May 1 in half of the years, after May 13 in 1 year out of 10. Fall: the first frost comes before September 23 in 1 year out of 10, before October 7 in half of the years, before October 20 in 9 years out of 10. Typical frost-free season: 160 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 1First frost ~Oct 7Frost season at Sanborn, IASpring: a frost after April 16 in 9 years out of 10, after May 1 in half of the years, after May 13 in 1 year out of 10. Fall: the first frost comes before September 23 in 1 year out of 10, before October 7 in half of the years, before October 20 in 9 years out of 10. Typical frost-free season: 160 days.JFMAMJJASONDLast frost ~May 1First frost ~Oct 7
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 27 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 13September 23
50% (typical)May 1October 7
90% (likely)April 16October 20
Frost-free season (32°F, 50% chance)
160 days
Hard frost (28°F), last in spring, 50% chance after
April 20
Hard frost (28°F), first in fall, 50% chance before
October 17

The last 15 years (2006–2020 normals)

Typical last frost May 1 (same as the 30-year normal), typical first fall frost October 11 (4 days later). Frost-free season 163 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 Sanborn: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 13, 20% May 8, 30% May 5, 40% May 2, 50% May 1, 60% April 28, 70% April 25, 80% April 21, 90% April 16. Observed last spring frost in recent years: 2021 May 7, 2022 April 28, 2023 May 2, 2024 April 22, 2025 April 19, 2026 May 7.Spring: last frostChance of a frost after this date10%50%90%May 1May 13May 1Apr 162021: May 72022: April 282023: May 22024: April 222025: April 192026: May 7Fall at Sanborn: chance of a frost before this dateFall, chance of a frost before the date: 10% September 23, 20% September 28, 30% October 1, 40% October 4, 50% October 7, 60% October 10, 70% October 12, 80% October 16, 90% October 20. Observed first fall frost in recent years: 2021 October 16, 2022 September 28, 2023 October 8, 2024 October 14, 2025 October 22.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 23Oct 7Oct 202021: October 162022: September 282023: October 82024: October 142025: October 22
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 7October 16
2022April 28September 28
2023May 2October 8
2024April 22October 14
2025April 19October 22
2026May 7season not over yet

What these dates mean

May 13 is the cautious spring date for light frost (32 °F) in Sanborn, with a 10 % chance of a frost later; it lets a gardener set out tender crops with relatively low risk. The early spring gamble of April 16 carries a 90 % chance of a frost later, while the median May 1 is the 50 % date, marking an even-odds point for a frost after it. September 23 is the cautious fall date, with a 10 % chance of a frost earlier, giving a gardener a reliable point to finish harvesting tender crops. The late fall gamble of October 20 carries a 90 % chance of a frost earlier, and the median October 7 is the 50 % date, indicating even odds for a frost before it.

For light frost, the 50 % dates are May 1 in spring and October 7 in fall, each representing a fifty-fifty chance of frost after or before respectively. The hard-frost 50 % dates are April 20 and October 17; a hard frost at 28 °F can damage plants more severely than a light frost at 32 °F.

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 23" 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 Sanborn, IANumbered nearest stations: 1 — Primghar, IA — 7 mi; 2 — Sheldon, IA — 10 mi; 3 — Sibley, IA — 16 mi; 4 — Lake Park, IA — 25 mi; 5 — Spencer, IA — 26 mi.IAMNSD25 mi · 40 km1. Primghar, IA — 7 mi12. Sheldon, IA — 10 mi23. Sibley, IA — 16 mi34. Lake Park, IA — 25 mi45. Spencer, IA — 26 mi5
  1. Primghar, IA 7 mi (11 km)
  2. Sheldon, IA 10 mi (16 km)
  3. Sibley, IA 16 mi (26 km)
  4. Lake Park, IA 25 mi (40 km)
  5. Spencer, IA 26 mi (42 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: 43.1792, -95.6603.