U.S. Frost Dates by Weather Station

NOAA station USC00394516 · South Dakota

Frost Dates for Kennebec, SD

NOAA weather station Kennebec (USC00394516), South Dakota · elevation 1681 ft (512 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 26only 1 spring in 10 still has a frost later
  • Typical last frostMay 1250% chance of a frost after it
  • Typical first fall frostSeptember 2850% chance of a frost before it
  • Frost-free season137 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Kennebec, SDSpring: a frost after April 29 in 9 years out of 10, after May 12 in half of the years, after May 26 in 1 year out of 10. Fall: the first frost comes before September 15 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: 137 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 12First frost ~Sep 28Frost season at Kennebec, SDSpring: a frost after April 29 in 9 years out of 10, after May 12 in half of the years, after May 26 in 1 year out of 10. Fall: the first frost comes before September 15 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: 137 days.JFMAMJJASONDLast frost ~May 12First 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 28 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 26September 15
50% (typical)May 12September 28
90% (likely)April 29October 10
Frost-free season (32°F, 50% chance)
137 days
Hard frost (28°F), last in spring, 50% chance after
May 3
Hard frost (28°F), first in fall, 50% chance before
October 5

The last 15 years (2006–2020 normals)

Typical last frost May 12 (same as the 30-year normal), typical first fall frost September 30 (2 days later). Frost-free season 139 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 Kennebec: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 26, 20% May 21, 30% May 17, 40% May 14, 50% May 12, 60% May 9, 70% May 7, 80% May 4, 90% April 29. Observed last spring frost in recent years: 2021 May 12, 2022 May 22, 2023 May 3, 2024 May 3, 2025 April 22, 2026 May 21.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 26May 12Apr 292021: May 122022: May 222023: May 32024: May 32025: April 222026: May 21Fall at Kennebec: chance of a frost before this dateFall, chance of a frost before the date: 10% September 15, 20% September 19, 30% September 23, 40% September 25, 50% September 28, 60% October 1, 70% October 3, 80% October 6, 90% October 10. Observed first fall frost in recent years: 2021 October 14, 2022 October 7, 2023 October 7, 2024 October 1, 2025 October 13.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 15Sep 28Oct 102021: October 142022: October 72023: October 72024: October 12025: October 13
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 12October 14
2022May 22October 7
2023May 3October 7
2024May 3October 1
2025April 22October 13
2026May 21season not over yet

What these dates mean

The cautious fall date for finishing the harvest in Kennebec is September 15, when there is only a 10 % chance that a light frost has arrived earlier.

For tender crops in spring, the cautious date is May 26, which carries a 10 % chance of a light frost later; planting on April 29 would be a gamble with a 90 % chance of frost later. The median dates, May 12 and September 28, each represent an even-odds (50 %) chance of a light frost occurring, providing a reference point for risk assessment. The hard-frost median dates are May 3 in spring and October 5 in fall.

A hard frost at 28 °F can kill or severely damage plants that would survive a light 32 °F frost, making it a more critical 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 26" 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 15" 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 Kennebec, SDNumbered nearest stations: 1 — Chamberlain, SD — 30 mi; 2 — Pierre, SD — 39 mi; 3 — Murdo, SD — 42 mi; 4 — Highmore, SD — 47 mi; 5 — Academy, SD — 49 mi.25 mi · 40 km1. Chamberlain, SD — 30 mi12. Pierre, SD — 39 mi23. Murdo, SD — 42 mi34. Highmore, SD — 47 mi45. Academy, SD — 49 mi5
  1. Chamberlain, SD 30 mi (48 km)
  2. Pierre, SD 39 mi (63 km)
  3. Murdo, SD 42 mi (68 km)
  4. Highmore, SD 47 mi (76 km)
  5. Academy, SD 49 mi (79 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: 43.9025, -99.8583.