U.S. Frost Dates by Weather Station

NOAA station USC00393868 · South Dakota

Frost Dates for Hill City, SD

NOAA weather station Hill City (USC00393868), South Dakota · elevation 4946 ft (1508 m) · hardiness zone 4b*

  • Lower-risk planting dateafter June 19only 1 spring in 10 still has a frost later
  • Typical last frostJune 150% chance of a frost after it
  • Typical first fall frostSeptember 1050% chance of a frost before it
  • Frost-free season102 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Hill City, SDSpring: a frost after May 18 in 9 years out of 10, after June 1 in half of the years, after June 19 in 1 year out of 10. Fall: the first frost comes before August 29 in 1 year out of 10, before September 10 in half of the years, before September 26 in 9 years out of 10. Typical frost-free season: 102 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Jun 1First frost ~Sep 10Frost season at Hill City, SDSpring: a frost after May 18 in 9 years out of 10, after June 1 in half of the years, after June 19 in 1 year out of 10. Fall: the first frost comes before August 29 in 1 year out of 10, before September 10 in half of the years, before September 26 in 9 years out of 10. Typical frost-free season: 102 days.JFMAMJJASONDLast frost ~Jun 1First frost ~Sep 10
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)June 19August 29
50% (typical)June 1September 10
90% (likely)May 18September 26
Frost-free season (32°F, 50% chance)
102 days
Hard frost (28°F), last in spring, 50% chance after
May 18
Hard frost (28°F), first in fall, 50% chance before
September 21

The last 15 years (2006–2020 normals)

Typical last frost May 28 (4 days earlier than the 30-year normal), typical first fall frost September 13 (3 days later). Frost-free season 106 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 Hill City: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 19, 20% June 12, 30% June 7, 40% June 3, 50% June 1, 60% May 29, 70% May 25, 80% May 22, 90% May 18. Observed last spring frost in recent years: 2021 May 31, 2022 June 26, 2023 May 20, 2024 June 19, 2025 June 4, 2026 June 15.Spring: last frostChance of a frost after this date10%50%90%Jun 1Jul 1Jun 19Jun 1May 182021: May 312022: June 262023: May 202024: June 192025: June 42026: June 15Fall at Hill City: chance of a frost before this dateFall, chance of a frost before the date: 10% August 29, 20% September 2, 30% September 5, 40% September 7, 50% September 10, 60% September 13, 70% September 17, 80% September 21, 90% September 26. Observed first fall frost in recent years: 2021 September 18, 2022 September 10, 2023 September 25, 2024 September 22, 2025 August 31.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Aug 29Sep 10Sep 262021: September 182022: September 102023: September 252024: September 222025: August 31
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 31September 18
2022June 26September 10
2023May 20September 25
2024June 19September 22
2025June 4August 31
2026June 15season not over yet

What these dates mean

Hill City enjoys a 102-day span between the two 32°F 50% dates, June 1 and September 10, and that interval defines the period when the chance of a light frost is below fifty percent. June 1 marks the point where there is a 50% chance of a light frost occurring later in the season, while September 10 marks the point where there is a 50% chance of a light frost occurring earlier.

Gardeners who prefer a cautious approach should wait until the June 19 date, which carries only a 10% chance of a light frost later, before setting out tender crops, while planting on May 18 carries a 90% chance and is a gamble. In the fall, finishing tender crops by August 29 keeps the frost risk at 10%, whereas September 26 represents a 90% chance of a frost earlier and is risky. A hard frost at 28°F is a greater threat because it can damage plant tissue that survives a 32°F light frost.

How to read the probabilities

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

  • Spring: "10% after June 19" 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 August 29" 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 Hill City, SDNumbered nearest stations: 1 — Mount Rushmore National Memorial, SD — 6 mi; 2 — near Colonial Pine Hills, SD — 10 mi; 3 — Custer, SD — 11 mi; 4 — near Blackhawk, SD — 19 mi; 5 — Rapid City (Airport), SD — 26 mi.WY25 mi · 40 km1. Mount Rushmore National Memorial, SD — 6 mi12. near Colonial Pine Hills, SD — 10 mi23. Custer, SD — 11 mi34. near Blackhawk, SD — 19 mi45. Rapid City (Airport), SD — 26 mi5
  1. Mount Rushmore National Memorial, SD 6 mi (10 km)
  2. near Colonial Pine Hills, SD 10 mi (15 km)
  3. Custer, SD 11 mi (18 km)
  4. near Blackhawk, SD 19 mi (30 km)
  5. Rapid City (Airport), SD 26 mi (42 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: 43.9342, -103.5572.