U.S. Frost Dates by Weather Station

NOAA station USC00391076 · South Dakota

Frost Dates for Brookings, SD

NOAA weather station Brookings 2 NE (USC00391076), South Dakota · elevation 1639 ft (500 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 19only 1 spring in 10 still has a frost later
  • Typical last frostMay 650% chance of a frost after it
  • Typical first fall frostOctober 150% chance of a frost before it
  • Frost-free season145 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Brookings, SDSpring: a frost after April 25 in 9 years out of 10, after May 6 in half of the years, after May 19 in 1 year out of 10. Fall: the first frost comes before September 17 in 1 year out of 10, before October 1 in half of the years, before October 13 in 9 years out of 10. Typical frost-free season: 145 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 6First frost ~Oct 1Frost season at Brookings, SDSpring: a frost after April 25 in 9 years out of 10, after May 6 in half of the years, after May 19 in 1 year out of 10. Fall: the first frost comes before September 17 in 1 year out of 10, before October 1 in half of the years, before October 13 in 9 years out of 10. Typical frost-free season: 145 days.JFMAMJJASONDLast frost ~May 6First 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 30 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 19September 17
50% (typical)May 6October 1
90% (likely)April 25October 13
Frost-free season (32°F, 50% chance)
145 days
Hard frost (28°F), last in spring, 50% chance after
April 28
Hard frost (28°F), first in fall, 50% chance before
October 8

The last 15 years (2006–2020 normals)

Typical last frost May 5 (1 day earlier than the 30-year normal), typical first fall frost October 4 (3 days later). Frost-free season 151 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 Brookings: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 19, 20% May 14, 30% May 11, 40% May 9, 50% May 6, 60% May 4, 70% May 2, 80% April 29, 90% April 25. Observed last spring frost in recent years: 2021 May 11, 2022 April 27, 2023 May 3, 2024 April 24, 2025 April 29, 2026 May 20.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 19May 6Apr 252021: May 112022: April 272023: May 32024: April 242025: April 292026: May 20Fall at Brookings: chance of a frost before this dateFall, chance of a frost before the date: 10% September 17, 20% September 22, 30% September 25, 40% September 29, 50% October 1, 60% October 3, 70% October 5, 80% October 9, 90% October 13. Observed first fall frost in recent years: 2021 October 16, 2022 October 7, 2023 October 7, 2024 October 4, 2025 October 22.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 17Oct 1Oct 132021: October 162022: October 72023: October 72024: October 42025: 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 16
2022April 27October 7
2023May 3October 7
2024April 24October 4
2025April 29October 22
2026May 20season not over yet

What these dates mean

May 19 is the cautious spring date for Brookings; with only a 10 % chance of a light frost later, it marks the point when a gardener can set out tender crops with relatively low risk. The equally cautious fall date is September 17, when there is just a 10 % chance that a light frost has already arrived, allowing the final harvest of tender crops.

The 50 % dates are May 6 and October 1; each represents an even-odds point, meaning a 50 % chance of a light frost later than May 6 in spring and a 50 % chance of a light frost earlier than October 1 in fall. The hard-frost 50 % dates are April 28 and October 8, and a hard frost at 28 °F can damage 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 19" 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 17" 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 Brookings, SDNumbered nearest stations: 1 — Flandreau, SD — 21 mi; 2 — Madison, SD — 28 mi; 3 — Clear Lake, SD — 30 mi; 4 — Pipestone, MN — 31 mi; 5 — Canby, MN — 37 mi.SDMN25 mi · 40 km1. Flandreau, SD — 21 mi12. Madison, SD — 28 mi23. Clear Lake, SD — 30 mi34. Pipestone, MN — 31 mi45. Canby, MN — 37 mi5
  1. Flandreau, SD 21 mi (33 km)
  2. Madison, SD 28 mi (45 km)
  3. Clear Lake, SD 30 mi (49 km)
  4. Pipestone, MN 31 mi (49 km)
  5. Canby, MN 37 mi (59 km)

Sources

* Hardiness zone 4b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 44.325, -96.7686.