U.S. Frost Dates by Weather Station

NOAA station USC00397882 · South Dakota

Frost Dates for Spearfish, SD

NOAA weather station Spearfish (USC00397882), South Dakota · elevation 3633 ft (1107 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 25only 1 spring in 10 still has a frost later
  • Typical last frostMay 1250% chance of a frost after it
  • Typical first fall frostOctober 250% chance of a frost before it
  • Frost-free season143 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Spearfish, SDSpring: a frost after April 29 in 9 years out of 10, after May 12 in half of the years, after May 25 in 1 year out of 10. Fall: the first frost comes before September 21 in 1 year out of 10, before October 2 in half of the years, before October 17 in 9 years out of 10. Typical frost-free season: 143 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 12First frost ~Oct 2Frost season at Spearfish, SDSpring: a frost after April 29 in 9 years out of 10, after May 12 in half of the years, after May 25 in 1 year out of 10. Fall: the first frost comes before September 21 in 1 year out of 10, before October 2 in half of the years, before October 17 in 9 years out of 10. Typical frost-free season: 143 days.JFMAMJJASONDLast frost ~May 12First frost ~Oct 2
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.Today

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 25September 21
50% (typical)May 12October 2
90% (likely)April 29October 17
Frost-free season (32°F, 50% chance)
143 days
Hard frost (28°F), last in spring, 50% chance after
April 30
Hard frost (28°F), first in fall, 50% chance before
October 12

The last 15 years (2006–2020 normals)

Typical last frost May 12 (same as the 30-year normal), typical first fall frost October 3 (1 day later). Frost-free season 143 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 Spearfish: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 25, 20% May 20, 30% May 17, 40% May 15, 50% May 12, 60% May 9, 70% May 6, 80% May 3, 90% April 29. Observed last spring frost in recent years: 2021 May 10, 2022 May 23, 2023 May 1, 2024 May 5, 2025 May 19, 2026 May 7.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 25May 12Apr 292021: May 102022: May 232023: May 12024: May 52025: May 192026: May 7Fall at Spearfish: chance of a frost before this dateFall, chance of a frost before the date: 10% September 21, 20% September 26, 30% September 29, 40% October 1, 50% October 2, 60% October 5, 70% October 9, 80% October 13, 90% October 17. Observed first fall frost in recent years: 2021 October 13, 2022 October 18, 2023 October 6, 2024 October 15, 2025 October 12.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 21Oct 2Oct 172021: October 132022: October 182023: October 62024: October 152025: October 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. ◆ 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 10October 13
2022May 23October 18
2023May 1October 6
2024May 5October 15
2025May 19October 12
2026May 7season not over yet

What these dates mean

Setting out tender crops on April 29 in Spearfish is a gamble, because there is a 90 % chance of a light frost later than that date. The 50 % date for light frost in spring is May 12; a gardener has an even chance of a frost after that point. The cautious spring date, May 25, carries only a 10 % chance of a later frost, making it the lower-risk option for planting tender varieties.

In the fall, the cautious date to finish harvesting tender crops is September 21, when only a 10 % chance of an earlier light frost exists; counting on crops as late as October 17 is a gamble with a 90 % chance of an earlier frost. The 50 % date for light frost in fall is October 2. Hard-frost risk is measured by the 50 % dates of April 30 in spring and October 12 in fall, and a hard frost at 28 °F is more damaging than a light frost at 32 °F because the lower temperature can injure or kill plant tissue that a light frost may spare.

How to read the probabilities

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

  • Spring: "10% after May 25" 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 Spearfish, SDNumbered nearest stations: 1 — Lead, SD — 12 mi; 2 — Belle Fourche, SD — 12 mi; 3 — near Sturgis, SD — 20 mi; 4 — Newell, SD — 27 mi; 5 — near Colonial Pine Hills, SD — 36 mi.SDWYMT25 mi · 40 km1. Lead, SD — 12 mi12. Belle Fourche, SD — 12 mi23. near Sturgis, SD — 20 mi34. Newell, SD — 27 mi45. near Colonial Pine Hills, SD — 36 mi5
  1. Lead, SD 12 mi (19 km)
  2. Belle Fourche, SD 12 mi (19 km)
  3. near Sturgis, SD 20 mi (33 km)
  4. Newell, SD 27 mi (43 km)
  5. near Colonial Pine Hills, SD 36 mi (57 km)

Sources

* Hardiness zone 5b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 44.4975, -103.8717.