U.S. Frost Dates by Weather Station

NOAA station USC00392984 · South Dakota

Frost Dates for Flandreau, SD

NOAA weather station Flandreau (USC00392984), South Dakota · elevation 1567 ft (478 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 17only 1 spring in 10 still has a frost later
  • Typical last frostMay 550% chance of a frost after it
  • Typical first fall frostOctober 150% chance of a frost before it
  • Frost-free season148 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Flandreau, SDSpring: a frost after April 23 in 9 years out of 10, after May 5 in half of the years, after May 17 in 1 year out of 10. Fall: the first frost comes before September 19 in 1 year out of 10, before October 1 in half of the years, before October 14 in 9 years out of 10. Typical frost-free season: 148 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 5First frost ~Oct 1Frost season at Flandreau, SDSpring: a frost after April 23 in 9 years out of 10, after May 5 in half of the years, after May 17 in 1 year out of 10. Fall: the first frost comes before September 19 in 1 year out of 10, before October 1 in half of the years, before October 14 in 9 years out of 10. Typical frost-free season: 148 days.JFMAMJJASONDLast frost ~May 5First 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.Today

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 17September 19
50% (typical)May 5October 1
90% (likely)April 23October 14
Frost-free season (32°F, 50% chance)
148 days
Hard frost (28°F), last in spring, 50% chance after
April 26
Hard frost (28°F), first in fall, 50% chance before
October 11

The last 15 years (2006–2020 normals)

Typical last frost May 5 (same as the 30-year normal), typical first fall frost October 5 (4 days later). Frost-free season 152 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 Flandreau: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 17, 20% May 13, 30% May 9, 40% May 7, 50% May 5, 60% May 3, 70% May 1, 80% April 28, 90% April 23. Observed last spring frost in recent years: 2021 May 13, 2022 May 5, 2023 May 4, 2024 April 25, 2025 April 30, 2026 May 20.Spring: last frostChance of a frost after this date10%50%90%May 1May 17May 5Apr 232021: May 132022: May 52023: May 42024: April 252025: April 302026: May 20Fall at Flandreau: chance of a frost before this dateFall, chance of a frost before the date: 10% September 19, 20% September 24, 30% September 27, 40% September 29, 50% October 1, 60% October 4, 70% October 7, 80% October 10, 90% October 14. Observed first fall frost in recent years: 2021 September 25, 2022 September 28, 2023 October 7, 2024 October 4, 2025 October 22.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 19Oct 1Oct 142021: September 252022: September 282023: 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 13September 25
2022May 5September 28
2023May 4October 7
2024April 25October 4
2025April 30October 22
2026May 20season not over yet

What these dates mean

Planting tender crops on April 23 in Flandreau carries a 90 % chance that a light frost will still occur later, making that timing a gamble for growers. The safer approach follows the cautious dates: May 17, when only a 10 % chance of a light frost remains, and September 19 in the fall, when there is likewise a 10 % chance that a light frost has already arrived.

The 50 % dates mark the point of even odds. The 50 % date is May 5 for spring light frost, meaning a 50 % chance of a frost later than this day, and the 50 % date is October 1 for fall light frost, meaning a 50 % chance of a frost earlier than this day. The hard-frost median dates are April 26 in spring and October 11 in fall; a hard frost at 28 °F can damage plants that survive a light frost at 32 °F, so those dates give a stricter warning.

How to read the probabilities

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

  • Spring: "10% after May 17" 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 19" 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 Flandreau, SDNumbered nearest stations: 1 — Pipestone, MN — 14 mi; 2 — Brookings, SD — 21 mi; 3 — Madison, SD — 25 mi; 4 — Lake Wilson, MN — 32 mi; 5 — Sioux Falls, SD — 33 mi.MNIA25 mi · 40 km1. Pipestone, MN — 14 mi12. Brookings, SD — 21 mi23. Madison, SD — 25 mi34. Lake Wilson, MN — 32 mi45. Sioux Falls, SD — 33 mi5
  1. Pipestone, MN 14 mi (22 km)
  2. Brookings, SD 21 mi (33 km)
  3. Madison, SD 25 mi (41 km)
  4. Lake Wilson, MN 32 mi (52 km)
  5. Sioux Falls, SD 33 mi (53 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: 44.0517, -96.5928.