U.S. Frost Dates by Weather Station

NOAA station USC00395456 · South Dakota

Frost Dates for Mellette, SD

NOAA weather station Mellette 4 W (USC00395456), South Dakota · elevation 1296 ft (395 m) · hardiness zone 4a*

  • Lower-risk planting dateafter May 23only 1 spring in 10 still has a frost later
  • Typical last frostMay 1150% chance of a frost after it
  • Typical first fall frostSeptember 2750% chance of a frost before it
  • Frost-free season137 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season at Mellette, SDSpring: a frost after April 29 in 9 years out of 10, after May 11 in half of the years, after May 23 in 1 year out of 10. Fall: the first frost comes before September 15 in 1 year out of 10, before September 27 in half of the years, before October 7 in 9 years out of 10. Typical frost-free season: 137 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 11First frost ~Sep 27Frost season at Mellette, SDSpring: a frost after April 29 in 9 years out of 10, after May 11 in half of the years, after May 23 in 1 year out of 10. Fall: the first frost comes before September 15 in 1 year out of 10, before September 27 in half of the years, before October 7 in 9 years out of 10. Typical frost-free season: 137 days.JFMAMJJASONDLast frost ~May 11First frost ~Sep 27
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 26 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 23September 15
50% (typical)May 11September 27
90% (likely)April 29October 7
Frost-free season (32°F, 50% chance)
137 days
Hard frost (28°F), last in spring, 50% chance after
May 2
Hard frost (28°F), first in fall, 50% chance before
October 4

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 1 (4 days later). Frost-free season 144 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 Mellette: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 23, 20% May 19, 30% May 16, 40% May 13, 50% May 11, 60% May 9, 70% May 6, 80% May 3, 90% April 29.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 23May 11Apr 29Fall at Mellette: chance of a frost before this dateFall, chance of a frost before the date: 10% September 15, 20% September 19, 30% September 22, 40% September 24, 50% September 27, 60% September 28, 70% October 1, 80% October 4, 90% October 7.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 15Sep 27Oct 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.

What these dates mean

The cautious fall date in Mellette for finishing the harvest is September 15, when there is only a 10 % chance that a light frost has arrived earlier. Gardeners who wait until this date reduce the likelihood of frost damage to tender crops at the end of the season.

The 50 % dates mark the point at which a light frost is equally likely to have occurred or not. In this location the median light-frost dates are May 11 in spring and September 27 in fall. The median hard-frost dates, when temperatures reach 28 °F, are May 2 and October 4.

For a cautious planting schedule, the spring light-frost date is May 23, which carries only a 10 % chance of a frost later in the season, while the fall cautious date remains September 15. A hard frost at 28 °F can injure plants that survive a light frost at 32 °F, making the hard-frost dates especially important for protecting vulnerable crops.

How to read the probabilities

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

  • Spring: "10% after May 23" 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 15" 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 Mellette, SDNumbered nearest stations: 1 — Aberdeen, SD — 22 mi; 2 — Faulkton, SD — 28 mi; 3 — Ipswich, SD — 30 mi; 4 — Columbia, SD — 42 mi; 5 — Roscoe, SD — 42 mi.SDND25 mi · 40 km1. Aberdeen, SD — 22 mi12. Faulkton, SD — 28 mi23. Ipswich, SD — 30 mi34. Columbia, SD — 42 mi45. Roscoe, SD — 42 mi5
  1. Aberdeen, SD 22 mi (36 km)
  2. Faulkton, SD 28 mi (45 km)
  3. Ipswich, SD 30 mi (48 km)
  4. Columbia, SD 42 mi (67 km)
  5. Roscoe, SD 42 mi (68 km)

Sources

* Hardiness zone 4a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 45.155, -98.5825.