U.S. Frost Dates by Weather Station

NOAA station USC00397545 · South Dakota

Frost Dates for Selby, SD

NOAA weather station Selby (USC00397545), South Dakota · elevation 1908 ft (582 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 21only 1 spring in 10 still has a frost later
  • Typical last frostMay 850% chance of a frost after it
  • Typical first fall frostOctober 150% chance of a frost before it
  • Frost-free season145 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Selby, SDSpring: a frost after April 26 in 9 years out of 10, after May 8 in half of the years, after May 21 in 1 year out of 10. Fall: the first frost comes before September 19 in 1 year out of 10, before October 1 in half of the years, before October 14 in 9 years out of 10. Typical frost-free season: 145 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 8First frost ~Oct 1Frost season at Selby, SDSpring: a frost after April 26 in 9 years out of 10, after May 8 in half of the years, after May 21 in 1 year out of 10. Fall: the first frost comes before September 19 in 1 year out of 10, before October 1 in half of the years, before October 14 in 9 years out of 10. Typical frost-free season: 145 days.JFMAMJJASONDLast frost ~May 8First frost ~Oct 1
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 21September 19
50% (typical)May 8October 1
90% (likely)April 26October 14
Frost-free season (32°F, 50% chance)
145 days
Hard frost (28°F), last in spring, 50% chance after
April 30
Hard frost (28°F), first in fall, 50% chance before
October 9

The last 15 years (2006–2020 normals)

Typical last frost May 8 (same as the 30-year normal), typical first fall frost October 6 (5 days later). Frost-free season 149 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 Selby: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 21, 20% May 17, 30% May 14, 40% May 11, 50% May 8, 60% May 6, 70% May 3, 80% April 30, 90% April 26. Observed last spring frost in recent years: 2021 May 11, 2022 May 4.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 21May 8Apr 262021: May 112022: May 4Fall at Selby: chance of a frost before this dateFall, chance of a frost before the date: 10% September 19, 20% September 24, 30% September 27, 40% September 29, 50% October 1, 60% October 4, 70% October 6, 80% October 10, 90% October 14. Observed first fall frost in recent years: 2021 September 21, 2022 October 7.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 19Oct 1Oct 142021: September 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 11September 21
2022May 4October 7
2023no datano data
2024no datano data
2025no datano data
2026no dataseason not over yet

What these dates mean

September 19 marks the cautious fall date for finishing the harvest in Selby, with only a 10 % chance that a light frost has arrived earlier.

The 50 % light-frost dates are May 8 in spring and October 1 in fall; at each of these points the chance of a frost is exactly fifty-fifty. The median hard-frost dates are April 30 and October 9, indicating an even chance of a 28 °F event. Gardeners can treat these dates as the moment when risk balances, guiding the timing of planting and any frost-watch preparations.

For a cautious spring schedule, gardeners look to May 21, which carries a 10 % chance of a frost later, while the gamble dates are April 26 (90 % chance) and October 14 (90 % chance). A hard frost at 28 °F can damage or kill plants that would survive a 32 °F light frost.

How to read the probabilities

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

  • Spring: "10% after May 21" 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 Selby, SDNumbered nearest stations: 1 — Pollock, SD — 30 mi; 2 — Roscoe, SD — 34 mi; 3 — McLaughlin, SD — 43 mi; 4 — Ipswich, SD — 48 mi; 5 — Ashley, ND — 49 mi.ND25 mi · 40 km1. Pollock, SD — 30 mi12. Roscoe, SD — 34 mi23. McLaughlin, SD — 43 mi34. Ipswich, SD — 48 mi45. Ashley, ND — 49 mi5
  1. Pollock, SD 30 mi (48 km)
  2. Roscoe, SD 34 mi (55 km)
  3. McLaughlin, SD 43 mi (69 km)
  4. Ipswich, SD 48 mi (78 km)
  5. Ashley, ND 49 mi (78 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: 45.51, -100.0356.