U.S. Frost Dates by Weather Station

NOAA station USC00392087 · South Dakota

Frost Dates for Custer, SD

NOAA weather station Custer (USC00392087), South Dakota · elevation 5480 ft (1670 m) · hardiness zone 5a*

  • Lower-risk planting dateafter June 1only 1 spring in 10 still has a frost later
  • Typical last frostMay 1850% chance of a frost after it
  • Typical first fall frostSeptember 2850% chance of a frost before it
  • Frost-free season129 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Custer, SDSpring: a frost after May 5 in 9 years out of 10, after May 18 in half of the years, after June 1 in 1 year out of 10. Fall: the first frost comes before September 10 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: 129 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 18First frost ~Sep 28Frost season at Custer, SDSpring: a frost after May 5 in 9 years out of 10, after May 18 in half of the years, after June 1 in 1 year out of 10. Fall: the first frost comes before September 10 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: 129 days.JFMAMJJASONDLast frost ~May 18First 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 26 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)June 1September 10
50% (typical)May 18September 28
90% (likely)May 5October 10
Frost-free season (32°F, 50% chance)
129 days
Hard frost (28°F), last in spring, 50% chance after
May 6
Hard frost (28°F), first in fall, 50% chance before
October 4

The last 15 years (2006–2020 normals)

Typical last frost May 20 (2 days later than the 30-year normal), typical first fall frost September 30 (2 days later). Frost-free season 132 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 Custer: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 1, 20% May 29, 30% May 25, 40% May 21, 50% May 18, 60% May 15, 70% May 12, 80% May 9, 90% May 5. Observed last spring frost in recent years: 2021 June 21, 2022 June 15, 2023 July 5, 2024 June 19, 2025 July 24, 2026 May 22.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jul 1Jun 1May 18May 52021: June 212022: June 152023: July 52024: June 192025: July 242026: May 22Fall at Custer: chance of a frost before this dateFall, chance of a frost before the date: 10% September 10, 20% September 17, 30% September 21, 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 September 13, 2022 October 9, 2023 September 5, 2024 October 11, 2025 September 5.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 10Sep 28Oct 102021: September 132022: October 92023: September 52024: October 112025: September 5
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
2021June 21September 13
2022June 15October 9
2023July 5September 5
2024June 19October 11
2025July 24September 5
2026May 22season not over yet

What these dates mean

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

The 50% light-frost date in spring is May 18, a 50 % chance of a frost later than this date, and the 50% date in fall is September 28, a 50 % chance of a frost earlier than this date.

For tender crops a cautious plan would wait until the June 1 date in spring, which carries only a 10 % chance of frost later, and aim to finish by the September 10 date in fall, which carries only a 10 % chance of frost earlier. Hard frosts at 28 °F, reflected by the median dates May 6 and October 4, are more damaging than 32 °F light frosts because the lower temperature can inflict deeper tissue injury.

How to read the probabilities

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

  • Spring: "10% after June 1" 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 10" 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 Custer, SDNumbered nearest stations: 1 — Mount Rushmore National Memorial, SD — 10 mi; 2 — Hill City, SD — 11 mi; 3 — Wind Cave, SD — 16 mi; 4 — near Colonial Pine Hills, SD — 21 mi; 5 — Hot Springs, SD — 24 mi.SDWYNE25 mi · 40 km1. Mount Rushmore National Memorial, SD — 10 mi12. Hill City, SD — 11 mi23. Wind Cave, SD — 16 mi34. near Colonial Pine Hills, SD — 21 mi45. Hot Springs, SD — 24 mi5
  1. Mount Rushmore National Memorial, SD 10 mi (17 km)
  2. Hill City, SD 11 mi (18 km)
  3. Wind Cave, SD 16 mi (27 km)
  4. near Colonial Pine Hills, SD 21 mi (34 km)
  5. Hot Springs, SD 24 mi (39 km)

Sources

* Hardiness zone 5a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 43.7744, -103.6119.