U.S. Frost Dates by Weather Station

NOAA station USC00390559 · South Dakota

Frost Dates for Belle Fourche, SD

NOAA weather station Belle Fourche (USC00390559), South Dakota · elevation 3020 ft (921 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 25only 1 spring in 10 still has a frost later
  • Typical last frostMay 1050% chance of a frost after it
  • Typical first fall frostSeptember 3050% chance of a frost before it
  • Frost-free season143 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Belle Fourche, SDSpring: a frost after April 27 in 9 years out of 10, after May 10 in half of the years, after May 25 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: 143 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 10First frost ~Sep 30Frost season at Belle Fourche, SDSpring: a frost after April 27 in 9 years out of 10, after May 10 in half of the years, after May 25 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: 143 days.JFMAMJJASONDLast frost ~May 10First 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 27 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 25September 16
50% (typical)May 10September 30
90% (likely)April 27October 13
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 10

The last 15 years (2006–2020 normals)

Typical last frost May 10 (same as the 30-year normal), typical first fall frost October 2 (2 days later). Frost-free season 144 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 Belle Fourche: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 25, 20% May 20, 30% May 16, 40% May 13, 50% May 10, 60% May 7, 70% May 4, 80% May 1, 90% April 27. Observed last spring frost in recent years: 2021 May 13.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 25May 10Apr 272021: May 13Fall at Belle Fourche: 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 3, 70% October 5, 80% October 9, 90% October 13. Observed first fall frost in recent years: 2021 September 22.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 16Sep 30Oct 132021: September 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 13September 22
2022no datano data
2023no datano data
2024no datano data
2025no datano data
2026no dataseason not over yet

What these dates mean

Setting out tender crops on April 27 in Belle Fourche carries a 90% chance of a light frost, making it a gamble for any garden that hopes to avoid frost damage. In contrast, waiting until the cautious spring date of May 25 reduces that risk to only 10%, giving a much lower likelihood of a light frost interfering with tender plantings.

The cautious fall date for finishing tender crops is September 16, when there is only a 10% chance that a light frost has already arrived; planting later than the gamble date of October 13 would face a 90% chance of frost. The 50% dates—May 10 in spring and September 30 in fall—mark the point where a light frost is equally likely to occur before or after them. Hard-frost median dates are April 30 and October 10; hard frost at 28 °F can damage plants more severely than a light frost at 32 °F, so those dates are important reference points for gardeners in this location.

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 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 Belle Fourche, SDNumbered nearest stations: 1 — Spearfish, SD — 12 mi; 2 — Newell, SD — 21 mi; 3 — Lead, SD — 23 mi; 4 — near Sturgis, SD — 26 mi; 5 — Devils Tower #2, WY — 43 mi.SDMT25 mi · 40 km1. Spearfish, SD — 12 mi12. Newell, SD — 21 mi23. Lead, SD — 23 mi34. near Sturgis, SD — 26 mi45. Devils Tower #2, WY — 43 mi5
  1. Spearfish, SD 12 mi (19 km)
  2. Newell, SD 21 mi (34 km)
  3. Lead, SD 23 mi (36 km)
  4. near Sturgis, SD 26 mi (41 km)
  5. Devils Tower #2, WY 43 mi (69 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: 44.6714, -103.8511.