U.S. Frost Dates by Weather Station

NOAA station USC00393832 · South Dakota

Frost Dates for Highmore, SD

NOAA weather station Highmore 1 W (USC00393832), South Dakota · elevation 1888 ft (576 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 28only 1 spring in 10 still has a frost later
  • Typical last frostMay 1250% chance of a frost after it
  • Typical first fall frostOctober 150% chance of a frost before it
  • Frost-free season142 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Highmore, SDSpring: a frost after April 28 in 9 years out of 10, after May 12 in half of the years, after May 28 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 14 in 9 years out of 10. Typical frost-free season: 142 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 12First frost ~Oct 1Frost season at Highmore, SDSpring: a frost after April 28 in 9 years out of 10, after May 12 in half of the years, after May 28 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 14 in 9 years out of 10. Typical frost-free season: 142 days.JFMAMJJASONDLast frost ~May 12First 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 28 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 28September 17
50% (typical)May 12October 1
90% (likely)April 28October 14
Frost-free season (32°F, 50% chance)
142 days
Hard frost (28°F), last in spring, 50% chance after
May 2
Hard frost (28°F), first in fall, 50% chance before
October 10

The last 15 years (2006–2020 normals)

Typical last frost May 10 (2 days earlier than the 30-year normal), typical first fall frost October 3 (2 days later). Frost-free season 145 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 Highmore: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 28, 20% May 22, 30% May 17, 40% May 14, 50% May 12, 60% May 8, 70% May 6, 80% May 2, 90% April 28. Observed last spring frost in recent years: 2021 May 13, 2022 May 22, 2023 May 2, 2024 May 4, 2025 April 30.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 28May 12Apr 282021: May 132022: May 222023: May 22024: May 42025: April 30Fall at Highmore: chance of a frost before this dateFall, chance of a frost before the date: 10% September 17, 20% September 22, 30% September 25, 40% September 29, 50% October 1, 60% October 4, 70% October 7, 80% October 10, 90% October 14. Observed first fall frost in recent years: 2022 October 7, 2023 October 7, 2024 October 14, 2025 October 13.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 17Oct 1Oct 142022: October 72023: October 72024: October 142025: 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 13incomplete record
2022May 22October 7
2023May 2October 7
2024May 4October 14
2025April 30October 13
2026incomplete recordseason not over yet

What these dates mean

May 28 is the cautious spring date in Highmore and it allows a gardener to plan setting out tender crops with only a 10 % chance that a light frost will occur later. The 50% spring light-frost date is May 12; at that date the chance of a frost is 50 %. The 50% fall light-frost date is October 1; at that date the chance of a frost is 50 %. The 50% hard-frost dates are May 2 in spring and October 10 in fall; these mark the median dates for a 28 °F frost, which can be more damaging than a 32 °F event. For the autumn season, September 17 is the cautious fall date, giving a 10 % chance that a light frost has arrived earlier and signalling when tender crops should be finished harvesting.

A hard frost at 28 °F can injure or kill plants that would survive a light frost at 32 °F, making it the more critical temperature threshold.

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 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 Highmore, SDNumbered nearest stations: 1 — Miller, SD — 23 mi; 2 — Onida, SD — 37 mi; 3 — Faulkton, SD — 39 mi; 4 — Pierre, SD — 42 mi; 5 — Kennebec, SD — 47 mi.25 mi · 40 km1. Miller, SD — 23 mi12. Onida, SD — 37 mi23. Faulkton, SD — 39 mi34. Pierre, SD — 42 mi45. Kennebec, SD — 47 mi5
  1. Miller, SD 23 mi (38 km)
  2. Onida, SD 37 mi (59 km)
  3. Faulkton, SD 39 mi (63 km)
  4. Pierre, SD 42 mi (68 km)
  5. Kennebec, SD 47 mi (76 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: 44.5222, -99.455.