U.S. Frost Dates by Weather Station

NOAA station USC00392429 · South Dakota

Frost Dates for Dupree, SD

NOAA weather station Dupree (USC00392429), South Dakota · elevation 2388 ft (728 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 22only 1 spring in 10 still has a frost later
  • Typical last frostMay 850% 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 zone4bcalculated*

The year at a glance

Frost season at Dupree, SDSpring: a frost after April 26 in 9 years out of 10, after May 8 in half of the years, after May 22 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 15 in 9 years out of 10. Typical frost-free season: 144 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 8First frost ~Oct 1Frost season at Dupree, SDSpring: a frost after April 26 in 9 years out of 10, after May 8 in half of the years, after May 22 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 15 in 9 years out of 10. Typical frost-free season: 144 days.JFMAMJJASONDLast frost ~May 8First 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 22September 17
50% (typical)May 8October 1
90% (likely)April 26October 15
Frost-free season (32°F, 50% chance)
144 days
Hard frost (28°F), last in spring, 50% chance after
April 29
Hard frost (28°F), first in fall, 50% chance before
October 9

The last 15 years (2006–2020 normals)

Typical last frost May 7 (1 day earlier than the 30-year normal), typical first fall frost October 4 (3 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 Dupree: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 22, 20% May 17, 30% May 13, 40% May 11, 50% May 8, 60% May 6, 70% May 3, 80% April 30, 90% April 26. Observed last spring frost in recent years: 2021 May 11, 2022 June 26, 2023 May 2, 2024 May 6.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jul 1May 22May 8Apr 262021: May 112022: June 262023: May 22024: May 6Fall at Dupree: chance of a frost before this dateFall, chance of a frost before the date: 10% September 17, 20% September 22, 30% September 26, 40% September 29, 50% October 1, 60% October 4, 70% October 6, 80% October 10, 90% October 15. Observed first fall frost in recent years: 2021 October 14, 2022 October 6, 2023 October 6, 2024 October 14.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 17Oct 1Oct 152021: October 142022: October 62023: October 62024: October 14
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 14
2022June 26October 6
2023May 2October 6
2024May 6October 14
2025no datano data
2026no dataseason not over yet

What these dates mean

The 144 days between the 50% dates in Dupree – May 8 and October 1 – define the period in which a light frost is equally likely to occur later or earlier, giving gardeners a rough window for tender crops. The 50% dates are not frost dates; they mark the midpoint of the risk curve for 32°F events.

In spring, the cautious date for setting out tender crops is May 22, which carries only a 10 % chance that a light frost will appear later; planting on April 26 would be a gamble with a 90 % chance of a later frost. In fall, the cautious date to finish harvesting tender crops is September 17, where there is only a 10 % chance that a light frost has already arrived; waiting until October 15 would be a gamble with a 90 % chance of an earlier frost.

A hard frost at 28°F can damage plants that survive a light frost at 32°F, making it a more serious threat.

How to read the probabilities

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

  • Spring: "10% after May 22" 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 Dupree, SDNumbered nearest stations: 1 — Dupree 15 SSE, SD — 14 mi; 2 — Glad Valley, SD — 26 mi; 3 — Milesville, SD — 37 mi; 4 — Timber Lake, SD — 37 mi; 5 — Maurine, SD — 49 mi.SD25 mi · 40 km1. Dupree 15 SSE, SD — 14 mi12. Glad Valley, SD — 26 mi23. Milesville, SD — 37 mi34. Timber Lake, SD — 37 mi45. Maurine, SD — 49 mi5
  1. Dupree 15 SSE, SD 14 mi (23 km)
  2. Glad Valley, SD 26 mi (43 km)
  3. Milesville, SD 37 mi (59 km)
  4. Timber Lake, SD 37 mi (59 km)
  5. Maurine, SD 49 mi (78 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: 45.0469, -101.6022.