U.S. Frost Dates by Weather Station

NOAA station USC00398116 · South Dakota

Frost Dates for Summit, SD

NOAA weather station Summit 1 W (USC00398116), South Dakota · elevation 1955 ft (596 m) · hardiness zone 4a*

  • Lower-risk planting dateafter May 28only 1 spring in 10 still has a frost later
  • Typical last frostMay 1450% chance of a frost after it
  • Typical first fall frostSeptember 2850% chance of a frost before it
  • Frost-free season136 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season at Summit, SDSpring: a frost after May 1 in 9 years out of 10, after May 14 in half of the years, after May 28 in 1 year out of 10. Fall: the first frost comes before September 13 in 1 year out of 10, before September 28 in half of the years, before October 10 in 9 years out of 10. Typical frost-free season: 136 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 14First frost ~Sep 28Frost season at Summit, SDSpring: a frost after May 1 in 9 years out of 10, after May 14 in half of the years, after May 28 in 1 year out of 10. Fall: the first frost comes before September 13 in 1 year out of 10, before September 28 in half of the years, before October 10 in 9 years out of 10. Typical frost-free season: 136 days.JFMAMJJASONDLast frost ~May 14First frost ~Sep 28
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 28September 13
50% (typical)May 14September 28
90% (likely)May 1October 10
Frost-free season (32°F, 50% chance)
136 days
Hard frost (28°F), last in spring, 50% chance after
May 4
Hard frost (28°F), first in fall, 50% chance before
October 4

The last 15 years (2006–2020 normals)

Typical last frost May 14 (same as the 30-year normal), typical first fall frost October 1 (3 days later). Frost-free season 138 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 Summit: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 28, 20% May 23, 30% May 20, 40% May 17, 50% May 14, 60% May 12, 70% May 9, 80% May 6, 90% May 1. Observed last spring frost in recent years: 2021 May 28, 2022 May 22, 2023 May 3, 2024 April 30, 2025 April 30, 2026 May 20.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 28May 14May 12021: May 282022: May 222023: May 32024: April 302025: April 302026: May 20Fall at Summit: chance of a frost before this dateFall, chance of a frost before the date: 10% September 13, 20% September 19, 30% September 22, 40% September 25, 50% September 28, 60% September 30, 70% October 2, 80% October 5, 90% October 10. Observed first fall frost in recent years: 2021 October 16, 2022 September 28, 2023 October 7, 2024 October 4, 2025 October 8.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 13Sep 28Oct 102021: October 162022: September 282023: October 72024: October 42025: October 8
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 28October 16
2022May 22September 28
2023May 3October 7
2024April 30October 4
2025April 30October 8
2026May 20season not over yet

What these dates mean

The 136 days between the 50% dates in Summit define the period when an even-odds frost risk exists: the 50% light-frost dates are May 14 and September 28, and the 50% hard-frost dates are May 4 and October 4. For a gardener this means a roughly fifty-fifty chance that a light frost could occur after May 14 in spring or before September 28 in fall, and a comparable chance that a hard frost could arrive after May 4 or before October 4.

A cautious planting plan follows the 10%-chance dates. In spring, the tender-crop window begins on May 28, where only a ten percent chance of a later light frost remains. In fall, finishing tender harvests by September 13 keeps the risk of an earlier light frost at ten percent. The opposite ends of each season—May 1 in spring and October 10 in fall—carry a ninety percent chance and are considered gambles.

Hard frost at 28 °F is more damaging than light frost at 32 °F because it can kill plant tissue that survives the milder temperature.

How to read the probabilities

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

  • Spring: "10% after May 28" 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 13" 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 Summit, SDNumbered nearest stations: 1 — Waubay National Wild Life, SD — 15 mi; 2 — Webster, SD — 22 mi; 3 — Browns Valley, MN — 23 mi; 4 — Sisseton, SD — 25 mi; 5 — Watertown, SD — 28 mi.SDMNND25 mi · 40 km1. Waubay National Wild Life, SD — 15 mi12. Webster, SD — 22 mi23. Browns Valley, MN — 23 mi34. Sisseton, SD — 25 mi45. Watertown, SD — 28 mi5
  1. Waubay National Wild Life, SD 15 mi (25 km)
  2. Webster, SD 22 mi (36 km)
  3. Browns Valley, MN 23 mi (37 km)
  4. Sisseton, SD 25 mi (40 km)
  5. Watertown, SD 28 mi (45 km)

Sources

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

Station coordinates: 45.3036, -97.0625.