U.S. Frost Dates by Weather Station

NOAA station USC00393316 · South Dakota

Frost Dates for Glad Valley, SD

NOAA weather station Glad Valley 2 W (USC00393316), South Dakota · elevation 2487 ft (758 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 24only 1 spring in 10 still has a frost later
  • Typical last frostMay 1150% chance of a frost after it
  • Typical first fall frostSeptember 3050% chance of a frost before it
  • Frost-free season140 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Glad Valley, SDSpring: a frost after April 30 in 9 years out of 10, after May 11 in half of the years, after May 24 in 1 year out of 10. Fall: the first frost comes before September 16 in 1 year out of 10, before September 30 in half of the years, before October 13 in 9 years out of 10. Typical frost-free season: 140 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 11First frost ~Sep 30Frost season at Glad Valley, SDSpring: a frost after April 30 in 9 years out of 10, after May 11 in half of the years, after May 24 in 1 year out of 10. Fall: the first frost comes before September 16 in 1 year out of 10, before September 30 in half of the years, before October 13 in 9 years out of 10. Typical frost-free season: 140 days.JFMAMJJASONDLast frost ~May 11First frost ~Sep 30
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 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 24September 16
50% (typical)May 11September 30
90% (likely)April 30October 13
Frost-free season (32°F, 50% chance)
140 days
Hard frost (28°F), last in spring, 50% chance after
May 2
Hard frost (28°F), first in fall, 50% chance before
October 7

The last 15 years (2006–2020 normals)

Typical last frost May 10 (1 day earlier than the 30-year normal), typical first fall frost October 4 (4 days later). Frost-free season 143 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 Glad Valley: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 24, 20% May 19, 30% May 16, 40% May 14, 50% May 11, 60% May 9, 70% May 6, 80% May 3, 90% April 30. Observed last spring frost in recent years: 2021 May 11, 2022 May 22, 2023 May 2, 2024 May 4, 2025 April 29, 2026 May 7.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 24May 11Apr 302021: May 112022: May 222023: May 22024: May 42025: April 292026: May 7Fall at Glad Valley: chance of a frost before this dateFall, chance of a frost before the date: 10% September 16, 20% September 21, 30% September 24, 40% September 27, 50% September 30, 60% October 2, 70% October 4, 80% October 8, 90% October 13. Observed first fall frost in recent years: 2021 October 14, 2022 October 7, 2023 October 6, 2024 October 13, 2025 October 13.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 16Sep 30Oct 132021: October 142022: October 72023: October 62024: October 132025: 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 11October 14
2022May 22October 7
2023May 2October 6
2024May 4October 13
2025April 29October 13
2026May 7season not over yet

What these dates mean

September 16 is the cautious fall date in Glad Valley for finishing the harvest of tender crops.

The 50% light-frost dates—May 11 in spring and September 30 in fall—mark the point where a light frost is equally likely to occur before or after the date, giving gardeners a statistical mid-point for planning. The hard-frost 50% dates are May 2 and October 7, which indicate the median odds for a 28 °F event.

For a low-risk schedule, the cautious spring date is May 24, when there is only a 10 % chance of a later light frost, while the cautious fall date remains September 16, with only a 10 % chance that a frost has arrived earlier. A hard frost at 28 °F is more damaging than a light frost at 32 °F because it can kill tissue that survives the milder temperature.

How to read the probabilities

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

  • Spring: "10% after May 24" 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 Glad Valley, SDNumbered nearest stations: 1 — Dupree, SD — 26 mi; 2 — Bison, SD — 33 mi; 3 — Timber Lake, SD — 36 mi; 4 — Dupree 15 SSE, SD — 41 mi; 5 — Lemmon, SD — 41 mi.SDND25 mi · 40 km1. Dupree, SD — 26 mi12. Bison, SD — 33 mi23. Timber Lake, SD — 36 mi34. Dupree 15 SSE, SD — 41 mi45. Lemmon, SD — 41 mi5
  1. Dupree, SD 26 mi (43 km)
  2. Bison, SD 33 mi (53 km)
  3. Timber Lake, SD 36 mi (57 km)
  4. Dupree 15 SSE, SD 41 mi (65 km)
  5. Lemmon, SD 41 mi (66 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: 45.4008, -101.8103.