U.S. Frost Dates by Weather Station

NOAA station USC00390043 · South Dakota

Frost Dates for Academy, SD

NOAA weather station Academy 2 NE (USC00390043), South Dakota · elevation 1681 ft (512 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 14only 1 spring in 10 still has a frost later
  • Typical last frostApril 3050% chance of a frost after it
  • Typical first fall frostOctober 850% chance of a frost before it
  • Frost-free season159 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Academy, SDSpring: a frost after April 16 in 9 years out of 10, after April 30 in half of the years, after May 14 in 1 year out of 10. Fall: the first frost comes before September 24 in 1 year out of 10, before October 8 in half of the years, before October 21 in 9 years out of 10. Typical frost-free season: 159 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 30First frost ~Oct 8Frost season at Academy, SDSpring: a frost after April 16 in 9 years out of 10, after April 30 in half of the years, after May 14 in 1 year out of 10. Fall: the first frost comes before September 24 in 1 year out of 10, before October 8 in half of the years, before October 21 in 9 years out of 10. Typical frost-free season: 159 days.JFMAMJJASONDLast frost ~Apr 30First frost ~Oct 8
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 14September 24
50% (typical)April 30October 8
90% (likely)April 16October 21
Frost-free season (32°F, 50% chance)
159 days
Hard frost (28°F), last in spring, 50% chance after
April 19
Hard frost (28°F), first in fall, 50% chance before
October 18

The last 15 years (2006–2020 normals)

Typical last frost April 30 (same as the 30-year normal), typical first fall frost October 11 (3 days later). Frost-free season 162 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 Academy: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 14, 20% May 8, 30% May 5, 40% May 2, 50% April 30, 60% April 28, 70% April 24, 80% April 20, 90% April 16. Observed last spring frost in recent years: 2021 May 11, 2022 May 22, 2023 May 2, 2024 April 24, 2025 April 21, 2026 May 20.Spring: last frostChance of a frost after this date10%50%90%May 1May 14Apr 30Apr 162021: May 112022: May 222023: May 22024: April 242025: April 212026: May 20Fall at Academy: chance of a frost before this dateFall, chance of a frost before the date: 10% September 24, 20% September 29, 30% October 1, 40% October 5, 50% October 8, 60% October 11, 70% October 14, 80% October 17, 90% October 21. Observed first fall frost in recent years: 2021 October 15, 2022 October 7, 2023 October 7, 2024 October 14, 2025 October 22.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 24Oct 8Oct 212021: October 152022: October 72023: October 72024: October 142025: October 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 11October 15
2022May 22October 7
2023May 2October 7
2024April 24October 14
2025April 21October 22
2026May 20season not over yet

What these dates mean

The cautious fall date in Academy for finishing the harvest is September 24, when there is only a 10 % chance that a light frost has already arrived. Planting tender crops after this date keeps the risk of an early frost low, while waiting until the later October 21 would be a gamble with a 90 % chance of frost already occurring.

In spring the 50 % date of April 30 marks a 50 % chance of a light frost later than this date; it is not itself a frost date. Gardeners who prefer a low-risk schedule tender crops for the cautious spring date of May 14, which carries a 10 % chance of frost later. The 50 % fall date of October 8 marks a 50 % chance of a light frost earlier than this date, and it serves the same reference point for autumn. The hard-frost 50 % dates are April 19 in spring and October 18 in fall, and a hard frost matters more than a light frost because the lower temperature of 28 °F can injure plants that survive 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 14" 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 24" 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 Academy, SDNumbered nearest stations: 1 — Chamberlain, SD — 21 mi; 2 — White Lake, SD — 24 mi; 3 — Gregory, SD — 26 mi; 4 — Pickstown, SD — 39 mi; 5 — Butte, NE — 41 mi.NE25 mi · 40 km1. Chamberlain, SD — 21 mi12. White Lake, SD — 24 mi23. Gregory, SD — 26 mi34. Pickstown, SD — 39 mi45. Butte, NE — 41 mi5
  1. Chamberlain, SD 21 mi (34 km)
  2. White Lake, SD 24 mi (38 km)
  3. Gregory, SD 26 mi (41 km)
  4. Pickstown, SD 39 mi (63 km)
  5. Butte, NE 41 mi (66 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: 43.4894, -99.0628.