U.S. Frost Dates by Weather Station

NOAA station USC00390701 · South Dakota

Frost Dates for Bison, SD

NOAA weather station Bison (USC00390701), South Dakota · elevation 2780 ft (847 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 24only 1 spring in 10 still has a frost later
  • Typical last frostMay 1050% chance of a frost after it
  • Typical first fall frostOctober 150% chance of a frost before it
  • Frost-free season144 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Bison, SDSpring: a frost after April 30 in 9 years out of 10, after May 10 in half of the years, after May 24 in 1 year out of 10. Fall: the first frost comes before September 16 in 1 year out of 10, before October 1 in half of the years, before October 15 in 9 years out of 10. Typical frost-free season: 144 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 10First frost ~Oct 1Frost season at Bison, SDSpring: a frost after April 30 in 9 years out of 10, after May 10 in half of the years, after May 24 in 1 year out of 10. Fall: the first frost comes before September 16 in 1 year out of 10, before October 1 in half of the years, before October 15 in 9 years out of 10. Typical frost-free season: 144 days.JFMAMJJASONDLast frost ~May 10First frost ~Oct 1
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 24September 16
50% (typical)May 10October 1
90% (likely)April 30October 15
Frost-free season (32°F, 50% chance)
144 days
Hard frost (28°F), last in spring, 50% chance after
May 1
Hard frost (28°F), first in fall, 50% chance before
October 9

The last 15 years (2006–2020 normals)

Typical last frost May 8 (2 days earlier than the 30-year normal), typical first fall frost October 3 (2 days later). Frost-free season 147 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 Bison: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 24, 20% May 18, 30% May 14, 40% May 12, 50% May 10, 60% May 7, 70% May 5, 80% May 2, 90% April 30. Observed last spring frost in recent years: 2021 May 28, 2022 May 23, 2023 May 2, 2024 May 4, 2025 May 2, 2026 May 19.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 24May 10Apr 302021: May 282022: May 232023: May 22024: May 42025: May 22026: May 19Fall at Bison: chance of a frost before this dateFall, chance of a frost before the date: 10% September 16, 20% September 22, 30% September 26, 40% September 29, 50% October 1, 60% October 3, 70% October 7, 80% October 11, 90% October 15. Observed first fall frost in recent years: 2021 October 14, 2022 October 6, 2023 October 6, 2024 October 13, 2025 October 13.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 16Oct 1Oct 152021: October 142022: October 62023: October 62024: October 132025: 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 28October 14
2022May 23October 6
2023May 2October 6
2024May 4October 13
2025May 2October 13
2026May 19season not over yet

What these dates mean

Setting out tender crops on April 30 in Bison is a gamble, because a light frost later than that date occurs with a 90% chance. For a lower risk, the cautious spring date is May 24, when only a 10% chance of a later frost remains.

The 50% light-frost date in spring is May 10 and the 50% light-frost date in fall is October 1; on those days the odds of a frost are even. The 50% hard-frost dates are May 1 for spring and October 9 for fall, indicating when a frost of 28 °F becomes as likely as not. In fall the cautious date to finish harvesting tender crops is September 16, which carries just a 10% chance that a frost has already arrived.

Hard frost matters more than light frost because temperatures of 28 °F can damage or kill plants that survive a 32 °F 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 24" 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 Bison, SDNumbered nearest stations: 1 — Lemmon, SD — 32 mi; 2 — Glad Valley, SD — 33 mi; 3 — Maurine, SD — 46 mi; 4 — Pretty Rock, ND — 53 mi; 5 — Dupree, SD — 54 mi.SDND25 mi · 40 km1. Lemmon, SD — 32 mi12. Glad Valley, SD — 33 mi23. Maurine, SD — 46 mi34. Pretty Rock, ND — 53 mi45. Dupree, SD — 54 mi5
  1. Lemmon, SD 32 mi (52 km)
  2. Glad Valley, SD 33 mi (53 km)
  3. Maurine, SD 46 mi (74 km)
  4. Pretty Rock, ND 53 mi (86 km)
  5. Dupree, SD 54 mi (86 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: 45.5286, -102.465.