U.S. Frost Dates by Weather Station

NOAA station USC00391972 · South Dakota

Frost Dates for Cottonwood, SD

NOAA weather station Cottonwood 2 E (USC00391972), South Dakota · elevation 2373 ft (723 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 29only 1 spring in 10 still has a frost later
  • Typical last frostMay 1650% chance of a frost after it
  • Typical first fall frostSeptember 2650% chance of a frost before it
  • Frost-free season132 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Cottonwood, SDSpring: a frost after May 4 in 9 years out of 10, after May 16 in half of the years, after May 29 in 1 year out of 10. Fall: the first frost comes before September 13 in 1 year out of 10, before September 26 in half of the years, before October 7 in 9 years out of 10. Typical frost-free season: 132 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 16First frost ~Sep 26Frost season at Cottonwood, SDSpring: a frost after May 4 in 9 years out of 10, after May 16 in half of the years, after May 29 in 1 year out of 10. Fall: the first frost comes before September 13 in 1 year out of 10, before September 26 in half of the years, before October 7 in 9 years out of 10. Typical frost-free season: 132 days.JFMAMJJASONDLast frost ~May 16First frost ~Sep 26
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 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 29September 13
50% (typical)May 16September 26
90% (likely)May 4October 7
Frost-free season (32°F, 50% chance)
132 days
Hard frost (28°F), last in spring, 50% chance after
May 5
Hard frost (28°F), first in fall, 50% chance before
October 4

The last 15 years (2006–2020 normals)

Typical last frost May 15 (1 day earlier than the 30-year normal), typical first fall frost September 29 (3 days later). Frost-free season 134 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 Cottonwood: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 29, 20% May 24, 30% May 21, 40% May 18, 50% May 16, 60% May 13, 70% May 11, 80% May 8, 90% May 4. Observed last spring frost in recent years: 2021 May 13, 2022 May 22, 2023 May 3, 2024 May 4, 2025 May 3, 2026 May 7.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 29May 16May 42021: May 132022: May 222023: May 32024: May 42025: May 32026: May 7Fall at Cottonwood: chance of a frost before this dateFall, chance of a frost before the date: 10% September 13, 20% September 18, 30% September 21, 40% September 23, 50% September 26, 60% September 28, 70% October 1, 80% October 3, 90% October 7. Observed first fall frost in recent years: 2021 October 14, 2022 October 8, 2023 October 7, 2024 October 1, 2025 September 6.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 13Sep 26Oct 72021: October 142022: October 82023: October 72024: October 12025: September 6
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 13October 14
2022May 22October 8
2023May 3October 7
2024May 4October 1
2025May 3September 6
2026May 7season not over yet

What these dates mean

The early spring date of May 4 is a gamble: there is a 90 % chance of a frost later than this date for tender crops in Cottonwood. Gardeners who prefer a lower risk wait until the cautious date of May 29, when only a 10 % chance of a frost remains.

The 50% date is May 16, meaning there is a 50 % chance of a frost later than this date, and the 50% date is September 26, meaning there is a 50 % chance of a frost earlier than this date. In the fall the cautious date to finish harvesting tender crops is September 13, which carries a 10 % chance of a frost having arrived earlier.

A hard frost at 28 °F, reflected by the median dates May 5 and October 4, can damage plants more severely than 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 29" 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 Cottonwood, SDNumbered nearest stations: 1 — Philip, SD — 14 mi; 2 — Interior, SD — 15 mi; 3 — Elm Springs, SD — 39 mi; 4 — Milesville, SD — 40 mi; 5 — Murdo, SD — 58 mi.25 mi · 40 km1. Philip, SD — 14 mi12. Interior, SD — 15 mi23. Elm Springs, SD — 39 mi34. Milesville, SD — 40 mi45. Murdo, SD — 58 mi5
  1. Philip, SD 14 mi (23 km)
  2. Interior, SD 15 mi (25 km)
  3. Elm Springs, SD 39 mi (63 km)
  4. Milesville, SD 40 mi (65 km)
  5. Murdo, SD 58 mi (93 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: 43.9611, -101.8606.