U.S. Frost Dates by Weather Station

NOAA station USC00393452 · South Dakota

Frost Dates for Gregory, SD

NOAA weather station Gregory (USC00393452), South Dakota · elevation 2160 ft (658 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 20only 1 spring in 10 still has a frost later
  • Typical last frostMay 650% chance of a frost after it
  • Typical first fall frostOctober 350% chance of a frost before it
  • Frost-free season149 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Gregory, SDSpring: a frost after April 23 in 9 years out of 10, after May 6 in half of the years, after May 20 in 1 year out of 10. Fall: the first frost comes before September 21 in 1 year out of 10, before October 3 in half of the years, before October 17 in 9 years out of 10. Typical frost-free season: 149 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 6First frost ~Oct 3Frost season at Gregory, SDSpring: a frost after April 23 in 9 years out of 10, after May 6 in half of the years, after May 20 in 1 year out of 10. Fall: the first frost comes before September 21 in 1 year out of 10, before October 3 in half of the years, before October 17 in 9 years out of 10. Typical frost-free season: 149 days.JFMAMJJASONDLast frost ~May 6First frost ~Oct 3
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 20September 21
50% (typical)May 6October 3
90% (likely)April 23October 17
Frost-free season (32°F, 50% chance)
149 days
Hard frost (28°F), last in spring, 50% chance after
April 26
Hard frost (28°F), first in fall, 50% chance before
October 13

The last 15 years (2006–2020 normals)

Typical last frost May 5 (1 day earlier than the 30-year normal), typical first fall frost October 8 (5 days later). Frost-free season 154 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 Gregory: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 20, 20% May 15, 30% May 11, 40% May 8, 50% May 6, 60% May 4, 70% May 1, 80% April 28, 90% April 23. Observed last spring frost in recent years: 2021 May 11, 2022 May 22, 2023 May 21, 2024 April 21, 2025 April 22, 2026 May 8.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 20May 6Apr 232021: May 112022: May 222023: May 212024: April 212025: April 222026: May 8Fall at Gregory: chance of a frost before this dateFall, chance of a frost before the date: 10% September 21, 20% September 25, 30% September 29, 40% October 1, 50% October 3, 60% October 6, 70% October 9, 80% October 13, 90% October 17. Observed first fall frost in recent years: 2021 October 14, 2022 October 7, 2023 October 7, 2024 October 14, 2025 October 19.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 21Oct 3Oct 172021: October 142022: October 72023: October 72024: October 142025: October 19
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 11October 14
2022May 22October 7
2023May 21October 7
2024April 21October 14
2025April 22October 19
2026May 8season not over yet

What these dates mean

In Gregory, the cautious spring date is May 20, when there is only a 10% chance of a light frost later; this date lets a gardener set out tender crops with minimal frost risk.

The 50% date is May 6, meaning a 50% chance of a light frost later than this date, and the 50% date for fall is October 3, meaning a 50% chance of a light frost earlier than this date. The cautious fall date is September 21, with only a 10% chance of a light frost earlier, marking a reasonable time to finish harvesting tender crops. The 50% hard-frost dates are April 26 in spring and October 13 in fall.

Hard frost, reaching 28 °F, can cause far greater damage to tender plants 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 20" 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 21" 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 Gregory, SDNumbered nearest stations: 1 — Academy, SD — 26 mi; 2 — Springview, NE — 32 mi; 3 — Chamberlain, SD — 35 mi; 4 — Butte, NE — 37 mi; 5 — Newport, NE — 44 mi.25 mi · 40 km1. Academy, SD — 26 mi12. Springview, NE — 32 mi23. Chamberlain, SD — 35 mi34. Butte, NE — 37 mi45. Newport, NE — 44 mi5
  1. Academy, SD 26 mi (41 km)
  2. Springview, NE 32 mi (52 km)
  3. Chamberlain, SD 35 mi (56 km)
  4. Butte, NE 37 mi (59 km)
  5. Newport, NE 44 mi (71 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: 43.2356, -99.4342.