U.S. Frost Dates by Weather Station

NOAA station USC00396304 · South Dakota

Frost Dates for Oral, SD

NOAA weather station Oral (USC00396304), South Dakota · elevation 2960 ft (902 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 28only 1 spring in 10 still has a frost later
  • Typical last frostMay 1550% chance of a frost after it
  • Typical first fall frostSeptember 2750% chance of a frost before it
  • Frost-free season133 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Oral, SDSpring: a frost after May 5 in 9 years out of 10, after May 15 in half of the years, after May 28 in 1 year out of 10. Fall: the first frost comes before September 11 in 1 year out of 10, before September 27 in half of the years, before October 8 in 9 years out of 10. Typical frost-free season: 133 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 15First frost ~Sep 27Frost season at Oral, SDSpring: a frost after May 5 in 9 years out of 10, after May 15 in half of the years, after May 28 in 1 year out of 10. Fall: the first frost comes before September 11 in 1 year out of 10, before September 27 in half of the years, before October 8 in 9 years out of 10. Typical frost-free season: 133 days.JFMAMJJASONDLast frost ~May 15First frost ~Sep 27
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 26 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 28September 11
50% (typical)May 15September 27
90% (likely)May 5October 8
Frost-free season (32°F, 50% chance)
133 days
Hard frost (28°F), last in spring, 50% chance after
May 6
Hard frost (28°F), first in fall, 50% chance before
October 5

The last 15 years (2006–2020 normals)

Typical last frost May 16 (1 day later than the 30-year normal), typical first fall frost September 28 (1 day later). Frost-free season 134 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 Oral: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 28, 20% May 23, 30% May 20, 40% May 17, 50% May 15, 60% May 13, 70% May 11, 80% May 8, 90% May 5. Observed last spring frost in recent years: 2021 May 13, 2022 May 25, 2023 May 3, 2024 May 5, 2025 May 17, 2026 May 20.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 28May 15May 52021: May 132022: May 252023: May 32024: May 52025: May 172026: May 20Fall at Oral: chance of a frost before this dateFall, chance of a frost before the date: 10% September 11, 20% September 18, 30% September 21, 40% September 24, 50% September 27, 60% September 29, 70% October 1, 80% October 3, 90% October 8. Observed first fall frost in recent years: 2021 October 11, 2022 October 9, 2023 October 6, 2025 September 6.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 11Sep 27Oct 82021: October 112022: October 92023: October 62025: September 6
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 13October 11
2022May 25October 9
2023May 3October 6
2024May 5incomplete record
2025May 17September 6
2026May 20season not over yet

What these dates mean

September 11 is the cautious fall date in Oral for finishing the harvest of tender crops, because there is only a 10 % chance of a light frost before that day. After that date the risk rises, and by October 8 the chance of a light frost reaches 90 %, making a late-season planting a gamble.

For gardeners, the 50 % dates mark the point where the odds of a light frost are even: May 15 in spring and September 27 in fall. The 50 % hard-frost dates are May 6 and October 5, indicating when a 28 °F frost is as likely as not. A hard frost at 28 °F can damage plants that survive a 32 °F light frost. The cautious plan therefore uses May 28 for setting out tender crops in spring (10 % chance of frost later) and September 11 for ending the tender-crop harvest in fall. The 90 % dates, May 5 and October 8, represent higher-risk choices.

How to read the probabilities

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

  • Spring: "10% after May 28" 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 11" 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 Oral, SDNumbered nearest stations: 1 — Hot Springs, SD — 11 mi; 2 — Wind Cave, SD — 15 mi; 3 — Oelrichs, SD — 15 mi; 4 — Custer, SD — 31 mi; 5 — Mount Rushmore National Memorial, SD — 34 mi.SDWYNE25 mi · 40 km1. Hot Springs, SD — 11 mi12. Wind Cave, SD — 15 mi23. Oelrichs, SD — 15 mi34. Custer, SD — 31 mi45. Mount Rushmore National Memorial, SD — 34 mi5
  1. Hot Springs, SD 11 mi (17 km)
  2. Wind Cave, SD 15 mi (24 km)
  3. Oelrichs, SD 15 mi (24 km)
  4. Custer, SD 31 mi (50 km)
  5. Mount Rushmore National Memorial, SD 34 mi (55 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: 43.4033, -103.2683.