U.S. Frost Dates by Weather Station

NOAA station USC00396212 · South Dakota

Frost Dates for Oelrichs, SD

NOAA weather station Oelrichs (USC00396212), South Dakota · elevation 3348 ft (1021 m) · hardiness zone 5a*

  • 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 3050% chance of a frost before it
  • Frost-free season137 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Oelrichs, SDSpring: a frost after May 4 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 16 in 1 year out of 10, before September 30 in half of the years, before October 13 in 9 years out of 10. Typical frost-free season: 137 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 15First frost ~Sep 30Frost season at Oelrichs, SDSpring: a frost after May 4 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 16 in 1 year out of 10, before September 30 in half of the years, before October 13 in 9 years out of 10. Typical frost-free season: 137 days.JFMAMJJASONDLast frost ~May 15First frost ~Sep 30
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 28 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 28September 16
50% (typical)May 15September 30
90% (likely)May 4October 13
Frost-free season (32°F, 50% chance)
137 days
Hard frost (28°F), last in spring, 50% chance after
May 6
Hard frost (28°F), first in fall, 50% chance before
October 9

The last 15 years (2006–2020 normals)

Typical last frost May 15 (same as the 30-year normal), typical first fall frost October 1 (1 day later). Frost-free season 139 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 Oelrichs: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 28, 20% May 24, 30% May 20, 40% May 17, 50% May 15, 60% May 12, 70% May 10, 80% May 7, 90% May 4. Observed last spring frost in recent years: 2021 May 12, 2022 May 23, 2023 May 2, 2025 May 3, 2026 May 20.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 28May 15May 42021: May 122022: May 232023: May 22025: May 32026: May 20Fall at Oelrichs: chance of a frost before this dateFall, chance of a frost before the date: 10% September 16, 20% September 21, 30% September 24, 40% September 27, 50% September 30, 60% October 2, 70% October 5, 80% October 8, 90% October 13. Observed first fall frost in recent years: 2021 October 13, 2022 October 8, 2023 October 6, 2025 October 13.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 16Sep 30Oct 132021: October 132022: October 82023: October 62025: October 13
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 13
2022May 23October 8
2023May 2October 6
2024incomplete recordincomplete record
2025May 3October 13
2026May 20season not over yet

What these dates mean

The 137-day span between the 32°F 50% dates, May 15 and September 30, frames the period when tender crops can be grown. The 50% dates mark the points at which a light frost has an even chance of occurring later in spring or earlier in fall, giving gardeners a statistical midpoint for planning.

For a cautious approach, the spring light-frost date of May 28 carries only a 10 % chance that a frost will come later, while the fall light-frost date of September 16 carries a 10 % chance that a frost has arrived earlier; planting or harvesting around those dates reduces exposure to frost risk. The median hard-frost dates, May 6 and October 9, show when a 28°F event is equally likely, and a hard frost can damage plant tissue that would survive the milder 32°F light frost.

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 16" 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 Oelrichs, SDNumbered nearest stations: 1 — Oral, SD — 15 mi; 2 — Hot Springs, SD — 21 mi; 3 — Chadron, NE — 28 mi; 4 — Wind Cave, SD — 28 mi; 5 — Custer, SD — 45 mi.SDWYNE25 mi · 40 km1. Oral, SD — 15 mi12. Hot Springs, SD — 21 mi23. Chadron, NE — 28 mi34. Wind Cave, SD — 28 mi45. Custer, SD — 45 mi5
  1. Oral, SD 15 mi (24 km)
  2. Hot Springs, SD 21 mi (34 km)
  3. Chadron, NE 28 mi (45 km)
  4. Wind Cave, SD 28 mi (45 km)
  5. Custer, SD 45 mi (72 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: 43.1878, -103.2372.