U.S. Frost Dates by Weather Station

NOAA station USC00134735 · Iowa

Frost Dates for Le Mars, IA

NOAA weather station Le Mars (USC00134735), Iowa · elevation 1195 ft (364 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 12only 1 spring in 10 still has a frost later
  • Typical last frostApril 3050% chance of a frost after it
  • Typical first fall frostOctober 450% chance of a frost before it
  • Frost-free season157 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Le Mars, IASpring: a frost after April 17 in 9 years out of 10, after April 30 in half of the years, after May 12 in 1 year out of 10. Fall: the first frost comes before September 21 in 1 year out of 10, before October 4 in half of the years, before October 19 in 9 years out of 10. Typical frost-free season: 157 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 30First frost ~Oct 4Frost season at Le Mars, IASpring: a frost after April 17 in 9 years out of 10, after April 30 in half of the years, after May 12 in 1 year out of 10. Fall: the first frost comes before September 21 in 1 year out of 10, before October 4 in half of the years, before October 19 in 9 years out of 10. Typical frost-free season: 157 days.JFMAMJJASONDLast frost ~Apr 30First frost ~Oct 4
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 12September 21
50% (typical)April 30October 4
90% (likely)April 17October 19
Frost-free season (32°F, 50% chance)
157 days
Hard frost (28°F), last in spring, 50% chance after
April 20
Hard frost (28°F), first in fall, 50% chance before
October 16

The last 15 years (2006–2020 normals)

Typical last frost May 2 (2 days later than the 30-year normal), typical first fall frost October 8 (4 days later). Frost-free season 161 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 Le Mars: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 12, 20% May 8, 30% May 5, 40% May 2, 50% April 30, 60% April 28, 70% April 24, 80% April 21, 90% April 17. Observed last spring frost in recent years: 2021 May 11, 2022 April 27, 2023 May 3, 2024 April 21, 2025 April 20, 2026 May 6.Spring: last frostChance of a frost after this date10%50%90%May 1May 12Apr 30Apr 172021: May 112022: April 272023: May 32024: April 212025: April 202026: May 6Fall at Le Mars: chance of a frost before this dateFall, chance of a frost before the date: 10% September 21, 20% September 25, 30% September 28, 40% October 1, 50% October 4, 60% October 7, 70% October 11, 80% October 15, 90% October 19. Observed first fall frost in recent years: 2021 October 22, 2022 October 7, 2023 October 7, 2024 October 14, 2025 October 22.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 21Oct 4Oct 192021: October 222022: October 72023: October 72024: 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 11October 22
2022April 27October 7
2023May 3October 7
2024April 21October 14
2025April 20October 22
2026May 6season not over yet

What these dates mean

Setting out tender crops on April 17 in Le Mars carries a 90 % chance of a light frost later, making it a gamble for early planting. Gardeners who prefer a lower risk wait until the cautious spring date of May 12, which has only a 10 % chance of a light frost later. In the autumn, the cautious date to finish tender crops is September 21, when only a 10 % chance exists of a light frost earlier.

The 50% spring date is April 30; at that point there is a 50 % chance of a light frost later. The 50% fall date is October 4; there is a 50 % chance of a light frost earlier.

Hard-frost risk is expressed by the 50% hard-frost dates of April 20 in spring and October 16 in fall, and a hard frost at 28 °F can injure plant tissue that survives 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 12" 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 21" 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 Le Mars, IANumbered nearest stations: 1 — Sioux Center, IA — 19 mi; 2 — Hawarden, IA — 23 mi; 3 — near Sioux City, IA — 29 mi; 4 — Cherokee, IA — 31 mi; 5 — Sheldon, IA — 31 mi.NESDMN25 mi · 40 km1. Sioux Center, IA — 19 mi12. Hawarden, IA — 23 mi23. near Sioux City, IA — 29 mi34. Cherokee, IA — 31 mi45. Sheldon, IA — 31 mi5
  1. Sioux Center, IA 19 mi (30 km)
  2. Hawarden, IA 23 mi (37 km)
  3. near Sioux City, IA 29 mi (47 km)
  4. Cherokee, IA 31 mi (50 km)
  5. Sheldon, IA 31 mi (50 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: 42.7817, -96.1458.