U.S. Frost Dates by Weather Station

NOAA station USC00394184 · South Dakota

Frost Dates for Interior, SD

NOAA weather station Interior 3 NE (USC00394184), South Dakota · elevation 2440 ft (744 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 20only 1 spring in 10 still has a frost later
  • Typical last frostMay 550% chance of a frost after it
  • Typical first fall frostOctober 750% chance of a frost before it
  • Frost-free season152 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Interior, SDSpring: a frost after April 22 in 9 years out of 10, after May 5 in half of the years, after May 20 in 1 year out of 10. Fall: the first frost comes before September 23 in 1 year out of 10, before October 7 in half of the years, before October 20 in 9 years out of 10. Typical frost-free season: 152 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 5First frost ~Oct 7Frost season at Interior, SDSpring: a frost after April 22 in 9 years out of 10, after May 5 in half of the years, after May 20 in 1 year out of 10. Fall: the first frost comes before September 23 in 1 year out of 10, before October 7 in half of the years, before October 20 in 9 years out of 10. Typical frost-free season: 152 days.JFMAMJJASONDLast frost ~May 5First frost ~Oct 7
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 20September 23
50% (typical)May 5October 7
90% (likely)April 22October 20
Frost-free season (32°F, 50% chance)
152 days
Hard frost (28°F), last in spring, 50% chance after
April 25
Hard frost (28°F), first in fall, 50% chance before
October 15

The last 15 years (2006–2020 normals)

Typical last frost May 5 (same as the 30-year normal), typical first fall frost October 7. Frost-free season 155 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 Interior: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 20, 20% May 13, 30% May 10, 40% May 7, 50% May 5, 60% May 3, 70% May 1, 80% April 28, 90% April 22. Observed last spring frost in recent years: 2021 May 10, 2022 May 22, 2023 May 1, 2024 April 22, 2025 April 19, 2026 May 7.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 20May 5Apr 222021: May 102022: May 222023: May 12024: April 222025: April 192026: May 7Fall at Interior: chance of a frost before this dateFall, chance of a frost before the date: 10% September 23, 20% September 28, 30% October 1, 40% October 4, 50% October 7, 60% October 9, 70% October 12, 80% October 16, 90% October 20. Observed first fall frost in recent years: 2021 October 14, 2022 October 8, 2023 October 26, 2024 October 25.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 23Oct 7Oct 202021: October 142022: October 82023: October 262024: October 25
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 14
2022May 22October 8
2023May 1October 26
2024April 22October 25
2025April 19incomplete record
2026May 7season not over yet

What these dates mean

May 20 is the cautious spring light-frost date; it gives gardeners enough confidence to set out tender crops, with only a 10 % chance of a frost occurring later. The earlier light-frost date of April 22 carries a 90 % chance and is a gamble, while the median May 5 marks the point where the odds of a frost later are even.

For interior South Dakota, the median light-frost dates—May 5 in spring and October 7 in fall—signify the moments when a frost is as likely as not. The cautious fall date, September 23, carries a 10 % chance of a frost earlier and therefore guides the latest time to finish harvesting tender crops. Hard-frost median dates are April 25 and October 15; a hard frost at 28 °F can injure plants that would survive a light frost at 32 °F.

How to read the probabilities

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

  • Spring: "10% after May 20" 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 23" 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 Interior, SDNumbered nearest stations: 1 — Cottonwood, SD — 15 mi; 2 — Philip, SD — 27 mi; 3 — Elm Springs, SD — 47 mi; 4 — Milesville, SD — 55 mi; 5 — Rapid City (Airport), SD — 59 mi.SD25 mi · 40 km1. Cottonwood, SD — 15 mi12. Philip, SD — 27 mi23. Elm Springs, SD — 47 mi34. Milesville, SD — 55 mi45. Rapid City (Airport), SD — 59 mi5
  1. Cottonwood, SD 15 mi (25 km)
  2. Philip, SD 27 mi (43 km)
  3. Elm Springs, SD 47 mi (76 km)
  4. Milesville, SD 55 mi (89 km)
  5. Rapid City (Airport), SD 59 mi (95 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: 43.7483, -101.9414.