U.S. Frost Dates by Weather Station

NOAA station USC00390128 · South Dakota

Frost Dates for Alexandria, SD

NOAA weather station Alexandria (USC00390128), South Dakota · elevation 1365 ft (416 m) · hardiness zone 5a*

  • 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 frostSeptember 2950% chance of a frost before it
  • Frost-free season143 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Alexandria, SDSpring: a frost after April 27 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 17 in 1 year out of 10, before September 29 in half of the years, before October 11 in 9 years out of 10. Typical frost-free season: 143 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 8First frost ~Sep 29Frost season at Alexandria, SDSpring: a frost after April 27 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 17 in 1 year out of 10, before September 29 in half of the years, before October 11 in 9 years out of 10. Typical frost-free season: 143 days.JFMAMJJASONDLast frost ~May 8First frost ~Sep 29
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 17
50% (typical)May 8September 29
90% (likely)April 27October 11
Frost-free season (32°F, 50% chance)
143 days
Hard frost (28°F), last in spring, 50% chance after
April 30
Hard frost (28°F), first in fall, 50% chance before
October 7

The last 15 years (2006–2020 normals)

Typical last frost May 7 (1 day earlier than the 30-year normal), typical first fall frost October 2 (3 days later). Frost-free season 147 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 Alexandria: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 21, 20% May 16, 30% May 14, 40% May 10, 50% May 8, 60% May 5, 70% May 3, 80% April 30, 90% April 27. Observed last spring frost in recent years: 2021 May 11, 2022 May 22, 2023 May 3, 2024 April 24, 2025 April 29.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 21May 8Apr 272021: May 112022: May 222023: May 32024: April 242025: April 29Fall at Alexandria: chance of a frost before this dateFall, chance of a frost before the date: 10% September 17, 20% September 21, 30% September 24, 40% September 27, 50% September 29, 60% October 1, 70% October 3, 80% October 7, 90% October 11. Observed first fall frost in recent years: 2021 October 15, 2022 October 7, 2023 October 7, 2024 October 4, 2025 October 22.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 17Sep 29Oct 112021: October 152022: October 72023: October 72024: October 42025: 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 11October 15
2022May 22October 7
2023May 3October 7
2024April 24October 4
2025April 29October 22
2026incomplete recordseason not over yet

What these dates mean

In Alexandria there are 143 days between the 32°F 50% dates, May 8 and September 29, and within that window tender crops can be grown.

The 50% dates mark the point at which the chance of a light frost is even, meaning a gardener should expect roughly equal odds of frost occurring after May 8 in spring or before September 29 in fall. For a cautious spring plan the 10 % risk date is May 21, the latest date to set out tender crops; in fall the cautious date is September 17, when there is only a 10 % chance that a light frost has arrived earlier, making it the preferred time to finish harvesting tender crops.

Hard frost at 28°F, recorded with median dates of April 30 and October 7, matters more than a 32°F light frost because the lower temperature can cause severe damage to plant tissue.

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 17" 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 Alexandria, SDNumbered nearest stations: 1 — Bridgewater, SD — 16 mi; 2 — Menno, SD — 31 mi; 3 — Madison, SD — 42 mi; 4 — White Lake, SD — 44 mi; 5 — Tyndall, SD — 46 mi.IAMN25 mi · 40 km1. Bridgewater, SD — 16 mi12. Menno, SD — 31 mi23. Madison, SD — 42 mi34. White Lake, SD — 44 mi45. Tyndall, SD — 46 mi5
  1. Bridgewater, SD 16 mi (26 km)
  2. Menno, SD 31 mi (50 km)
  3. Madison, SD 42 mi (68 km)
  4. White Lake, SD 44 mi (70 km)
  5. Tyndall, SD 46 mi (74 km)

Sources

* Hardiness zone 5a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 43.6514, -97.7981.