U.S. Frost Dates by Weather Station

NOAA station USC00399004 · South Dakota

Frost Dates for Webster, SD

NOAA weather station Webster (USC00399004), South Dakota · elevation 1861 ft (567 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 16only 1 spring in 10 still has a frost later
  • Typical last frostMay 450% chance of a frost after it
  • Typical first fall frostOctober 650% chance of a frost before it
  • Frost-free season156 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Webster, SDSpring: a frost after April 20 in 9 years out of 10, after May 4 in half of the years, after May 16 in 1 year out of 10. Fall: the first frost comes before September 25 in 1 year out of 10, before October 6 in half of the years, before October 20 in 9 years out of 10. Typical frost-free season: 156 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 4First frost ~Oct 6Frost season at Webster, SDSpring: a frost after April 20 in 9 years out of 10, after May 4 in half of the years, after May 16 in 1 year out of 10. Fall: the first frost comes before September 25 in 1 year out of 10, before October 6 in half of the years, before October 20 in 9 years out of 10. Typical frost-free season: 156 days.JFMAMJJASONDLast frost ~May 4First frost ~Oct 6
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 30 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 16September 25
50% (typical)May 4October 6
90% (likely)April 20October 20
Frost-free season (32°F, 50% chance)
156 days
Hard frost (28°F), last in spring, 50% chance after
April 25
Hard frost (28°F), first in fall, 50% chance before
October 16

The last 15 years (2006–2020 normals)

Typical last frost May 4 (same as the 30-year normal), typical first fall frost October 11 (5 days later). Frost-free season 159 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 Webster: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 16, 20% May 12, 30% May 9, 40% May 6, 50% May 4, 60% May 1, 70% April 29, 80% April 26, 90% April 20. Observed last spring frost in recent years: 2021 May 4, 2022 May 3, 2023 May 2, 2024 April 21, 2025 April 30, 2026 May 7.Spring: last frostChance of a frost after this date10%50%90%May 1May 16May 4Apr 202021: May 42022: May 32023: May 22024: April 212025: April 302026: May 7Fall at Webster: chance of a frost before this dateFall, chance of a frost before the date: 10% September 25, 20% September 29, 30% October 1, 40% October 4, 50% October 6, 60% October 9, 70% October 12, 80% October 15, 90% October 20. Observed first fall frost in recent years: 2021 October 21, 2022 October 7, 2023 October 7, 2024 October 15, 2025 October 22.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 25Oct 6Oct 202021: October 212022: October 72023: October 72024: October 152025: October 22
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 4October 21
2022May 3October 7
2023May 2October 7
2024April 21October 15
2025April 30October 22
2026May 7season not over yet

What these dates mean

The cautious fall date for finishing the harvest in Webster is September 25, when there is only a 10 % chance that a light frost has arrived earlier.

The 50% date in spring is May 4, marking an even chance of a frost occurring later, and the 50% date in fall is October 6, marking an even chance of a frost occurring earlier. A cautious spring plan therefore waits until the May 16 date, which carries a 10 % chance of frost later, before setting out tender crops; a cautious fall plan stops tender crops by the September 25 date. The 50% hard-frost dates are April 25 and October 16, and a hard frost at 28 °F can damage plants more severely than a light frost at 32 °F because the lower temperature penetrates tissue more deeply.

How to read the probabilities

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

  • Spring: "10% after May 16" 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 25" 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 Webster, SDNumbered nearest stations: 1 — Waubay National Wild Life, SD — 11 mi; 2 — Summit, SD — 22 mi; 3 — Sisseton, SD — 33 mi; 4 — Britton, SD — 33 mi; 5 — Watertown, SD — 35 mi.SDMNND25 mi · 40 km1. Waubay National Wild Life, SD — 11 mi12. Summit, SD — 22 mi23. Sisseton, SD — 33 mi34. Britton, SD — 33 mi45. Watertown, SD — 35 mi5
  1. Waubay National Wild Life, SD 11 mi (18 km)
  2. Summit, SD 22 mi (36 km)
  3. Sisseton, SD 33 mi (53 km)
  4. Britton, SD 33 mi (54 km)
  5. Watertown, SD 35 mi (56 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: 45.3331, -97.5228.