U.S. Frost Dates by Weather Station

NOAA station USC00394864 · South Dakota

Frost Dates for Lemmon, SD

NOAA weather station Lemmon (USC00394864), South Dakota · elevation 2567 ft (782 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 24only 1 spring in 10 still has a frost later
  • Typical last frostMay 1050% chance of a frost after it
  • Typical first fall frostSeptember 3050% chance of a frost before it
  • Frost-free season142 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Lemmon, SDSpring: a frost after April 30 in 9 years out of 10, after May 10 in half of the years, after May 24 in 1 year out of 10. Fall: the first frost comes before September 18 in 1 year out of 10, before September 30 in half of the years, before October 12 in 9 years out of 10. Typical frost-free season: 142 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 10First frost ~Sep 30Frost season at Lemmon, SDSpring: a frost after April 30 in 9 years out of 10, after May 10 in half of the years, after May 24 in 1 year out of 10. Fall: the first frost comes before September 18 in 1 year out of 10, before September 30 in half of the years, before October 12 in 9 years out of 10. Typical frost-free season: 142 days.JFMAMJJASONDLast frost ~May 10First 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 27 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 24September 18
50% (typical)May 10September 30
90% (likely)April 30October 12
Frost-free season (32°F, 50% chance)
142 days
Hard frost (28°F), last in spring, 50% chance after
May 1
Hard frost (28°F), first in fall, 50% chance before
October 9

The last 15 years (2006–2020 normals)

Typical last frost May 9 (1 day earlier than the 30-year normal), typical first fall frost October 3 (3 days later). Frost-free season 145 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 Lemmon: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 24, 20% May 19, 30% May 15, 40% May 13, 50% May 10, 60% May 8, 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 10Apr 302021: May 112022: May 222023: May 22024: May 42025: April 292026: May 7Fall at Lemmon: chance of a frost before this dateFall, chance of a frost before the date: 10% September 18, 20% September 22, 30% September 25, 40% September 28, 50% September 30, 60% October 2, 70% October 5, 80% October 8, 90% October 12. 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 18Sep 30Oct 122021: 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

The cautious fall date for finishing the harvest in Lemmon is September 18, when there is only a 10% chance that a light frost has arrived.

The 50% light-frost dates—May 10 in spring and September 30 in fall—represent the median odds, meaning a frost is as probable as not on those days. The record spans 27 years, and the interval between the two 32°F 50% dates is 142 days.

A cautious planting schedule therefore waits until May 24, the 10% spring light-frost date, before putting tender crops in the field, and aims to finish tender harvest by September 18, the 10% fall date. A hard frost at 28 °F is more damaging than a light frost at 32 °F because it can kill tissue that survives milder freezing.

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 18" 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 Lemmon, SDNumbered nearest stations: 1 — Pretty Rock, ND — 22 mi; 2 — Bison, SD — 32 mi; 3 — Glad Valley, SD — 41 mi; 4 — Heart Butte Dam, ND — 48 mi; 5 — New England, ND — 54 mi.NDMT25 mi · 40 km1. Pretty Rock, ND — 22 mi12. Bison, SD — 32 mi23. Glad Valley, SD — 41 mi34. Heart Butte Dam, ND — 48 mi45. New England, ND — 54 mi5
  1. Pretty Rock, ND 22 mi (35 km)
  2. Bison, SD 32 mi (52 km)
  3. Glad Valley, SD 41 mi (66 km)
  4. Heart Butte Dam, ND 48 mi (77 km)
  5. New England, ND 54 mi (86 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: 45.9397, -102.1575.