U.S. Frost Dates by Weather Station

NOAA station USW00024090 · South Dakota

Frost Dates for Rapid City (Airport), SD

NOAA weather station Rapid City Regional Airport (USW00024090), South Dakota · elevation 3160 ft (963 m) · hardiness zone 5a*

  • 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 frostOctober 150% chance of a frost before it
  • Frost-free season139 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Rapid City (Airport), SDSpring: a frost after May 1 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 16 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: 139 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 12First frost ~Oct 1Frost season at Rapid City (Airport), SDSpring: a frost after May 1 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 16 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: 139 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 27 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 26September 16
50% (typical)May 12October 1
90% (likely)May 1October 14
Frost-free season (32°F, 50% chance)
139 days
Hard frost (28°F), last in spring, 50% chance after
May 2
Hard frost (28°F), first in fall, 50% chance before
October 9

The last 15 years (2006–2020 normals)

Typical last frost May 12 (same as the 30-year normal), typical first fall frost October 2 (1 day later). Frost-free season 142 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 Rapid City (Airport): chance of a frost after this dateSpring, chance of a frost after the date: 10% May 26, 20% May 21, 30% May 18, 40% May 14, 50% May 12, 60% May 9, 70% May 7, 80% May 4, 90% May 1. Observed last spring frost in recent years: 2021 May 13, 2022 May 24, 2023 May 2, 2024 May 4, 2025 April 23, 2026 May 20.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 26May 12May 12021: May 132022: May 242023: May 22024: May 42025: April 232026: May 20Fall at Rapid City (Airport): chance of a frost before this dateFall, chance of a frost before the date: 10% September 16, 20% September 21, 30% September 25, 40% September 28, 50% October 1, 60% October 3, 70% October 5, 80% October 9, 90% October 14. Observed first fall frost in recent years: 2021 October 12, 2022 October 7, 2023 October 6, 2024 October 15, 2025 October 13.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 16Oct 1Oct 142021: October 122022: October 72023: October 62024: October 152025: 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 13October 12
2022May 24October 7
2023May 2October 6
2024May 4October 15
2025April 23October 13
2026May 20season not over yet

What these dates mean

Setting out tender crops on May 1 in Rapid City (Airport) carries a 90 % chance that a light frost will still occur, making it a high-risk gamble for growers. By contrast, the cautious spring date of May 26 has only a 10 % chance of a later frost, offering a much lower risk for planting vulnerable crops.

The 50 % date is May 12, when there is a 50 % chance of a frost later than this date, and the 50 % date is October 1, when there is a 50 % chance of a frost earlier than this date. For a conservative harvest, the cautious fall date is September 16, which has only a 10 % chance that a light frost has arrived earlier. A hard frost at 28 °F can damage plant tissue more severely than a light frost at 32 °F, so its timing is especially critical.

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 16" 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 Rapid City (Airport), SDNumbered nearest stations: 1 — near Blackhawk, SD — 13 mi; 2 — near Colonial Pine Hills, SD — 21 mi; 3 — Mount Rushmore National Memorial, SD — 23 mi; 4 — Hill City, SD — 26 mi; 5 — near Sturgis, SD — 33 mi.SDWY25 mi · 40 km1. near Blackhawk, SD — 13 mi12. near Colonial Pine Hills, SD — 21 mi23. Mount Rushmore National Memorial, SD — 23 mi34. Hill City, SD — 26 mi45. near Sturgis, SD — 33 mi5
  1. near Blackhawk, SD 13 mi (20 km)
  2. near Colonial Pine Hills, SD 21 mi (34 km)
  3. Mount Rushmore National Memorial, SD 23 mi (37 km)
  4. Hill City, SD 26 mi (42 km)
  5. near Sturgis, SD 33 mi (53 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: 44.0433, -103.0536.