U.S. Frost Dates by Weather Station

NOAA station USC00397277 · South Dakota

Frost Dates for Roscoe, SD

NOAA weather station Roscoe (USC00397277), South Dakota · elevation 1835 ft (559 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 20only 1 spring in 10 still has a frost later
  • Typical last frostMay 750% chance of a frost after it
  • Typical first fall frostOctober 350% chance of a frost before it
  • Frost-free season148 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Roscoe, SDSpring: a frost after April 24 in 9 years out of 10, after May 7 in half of the years, after May 20 in 1 year out of 10. Fall: the first frost comes before September 19 in 1 year out of 10, before October 3 in half of the years, before October 16 in 9 years out of 10. Typical frost-free season: 148 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 7First frost ~Oct 3Frost season at Roscoe, SDSpring: a frost after April 24 in 9 years out of 10, after May 7 in half of the years, after May 20 in 1 year out of 10. Fall: the first frost comes before September 19 in 1 year out of 10, before October 3 in half of the years, before October 16 in 9 years out of 10. Typical frost-free season: 148 days.JFMAMJJASONDLast frost ~May 7First 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 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 20September 19
50% (typical)May 7October 3
90% (likely)April 24October 16
Frost-free season (32°F, 50% chance)
148 days
Hard frost (28°F), last in spring, 50% chance after
April 29
Hard frost (28°F), first in fall, 50% chance before
October 12

The last 15 years (2006–2020 normals)

Typical last frost May 6 (1 day earlier than the 30-year normal), typical first fall frost October 6 (3 days later). Frost-free season 152 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 Roscoe: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 20, 20% May 15, 30% May 12, 40% May 9, 50% May 7, 60% May 4, 70% May 2, 80% April 30, 90% April 24. Observed last spring frost in recent years: 2021 May 11, 2022 May 22.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 20May 7Apr 242021: May 112022: May 22Fall at Roscoe: chance of a frost before this dateFall, chance of a frost before the date: 10% September 19, 20% September 24, 30% September 28, 40% September 30, 50% October 3, 60% October 5, 70% October 8, 80% October 12, 90% October 16. Observed first fall frost in recent years: 2021 October 21, 2022 October 7.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 19Oct 3Oct 162021: October 212022: October 7
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 21
2022May 22October 7
2023incomplete recordno data
2024no datano data
2025no datano data
2026no dataseason not over yet

What these dates mean

May 20 is the cautious spring date for Roscoe, South Dakota, and it marks the point at which a gardener can plan to set out tender crops with only a 10 % chance of a later light frost. The opposite cautious date in fall is September 19, when there is only a 10 % chance that a light frost has arrived, so harvesting tender crops can be finished with minimal risk.

The 50 % dates are the median points where the odds of a light frost are even. In spring the 50 % date is May 7 and in fall it is October 3; each represents a 50 % chance of frost later (spring) or earlier (fall). For hard frost, the 50 % dates are April 29 and October 12, and a hard frost at 28 °F can damage or kill plants that survive a light frost at 32 °F, making it a more critical threshold.

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 19" 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 Roscoe, SDNumbered nearest stations: 1 — Ipswich, SD — 14 mi; 2 — Faulkton, SD — 30 mi; 3 — Selby, SD — 34 mi; 4 — Ashley, ND — 41 mi; 5 — Mellette, SD — 42 mi.25 mi · 40 km1. Ipswich, SD — 14 mi12. Faulkton, SD — 30 mi23. Selby, SD — 34 mi34. Ashley, ND — 41 mi45. Mellette, SD — 42 mi5
  1. Ipswich, SD 14 mi (23 km)
  2. Faulkton, SD 30 mi (49 km)
  3. Selby, SD 34 mi (55 km)
  4. Ashley, ND 41 mi (65 km)
  5. Mellette, SD 42 mi (68 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: 45.4528, -99.3358.