U.S. Frost Dates by Weather Station

NOAA station USC00391777 · South Dakota

Frost Dates for Clear Lake, SD

NOAA weather station Clear Lake (USC00391777), South Dakota · elevation 1812 ft (552 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 21only 1 spring in 10 still has a frost later
  • Typical last frostMay 750% chance of a frost after it
  • Typical first fall frostOctober 150% chance of a frost before it
  • Frost-free season146 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Clear Lake, SDSpring: a frost after April 25 in 9 years out of 10, after May 7 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: 146 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 7First frost ~Oct 1Frost season at Clear Lake, SDSpring: a frost after April 25 in 9 years out of 10, after May 7 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: 146 days.JFMAMJJASONDLast frost ~May 7First 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 28 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 21September 19
50% (typical)May 7October 1
90% (likely)April 25October 14
Frost-free season (32°F, 50% chance)
146 days
Hard frost (28°F), last in spring, 50% chance after
April 29
Hard frost (28°F), first in fall, 50% chance before
October 10

The last 15 years (2006–2020 normals)

Typical last frost May 7 (same as the 30-year normal), typical first fall frost October 6 (5 days later). Frost-free season 150 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 Clear Lake: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 21, 20% May 15, 30% May 12, 40% May 10, 50% May 7, 60% May 5, 70% May 2, 80% April 30, 90% April 25.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 21May 7Apr 25Fall at Clear Lake: chance of a frost before this dateFall, chance of a frost before the date: 10% September 19, 20% September 23, 30% September 26, 40% September 29, 50% October 1, 60% October 3, 70% October 6, 80% October 10, 90% October 14.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 19Oct 1Oct 14
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 Clear Lake for finishing the harvest is September 19, when there is only a 10 % chance that a light frost has arrived.

The 50% date for light frost in spring is May 7, indicating an even odds chance of a frost occurring. The 50% date for light frost in fall is October 1. The 50% date for hard frost in spring is April 29, and for hard frost in fall it is October 10. For a cautious plan, tender crops should be set out no earlier than May 21 in spring, and harvesting should be completed by September 19 in fall.

A hard frost at 28 °F can injure plants that would normally survive a light frost at 32 °F, so it represents a greater risk.

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 Clear Lake, SDNumbered nearest stations: 1 — Canby, MN — 20 mi; 2 — Watertown, SD — 25 mi; 3 — Brookings, SD — 30 mi; 4 — Madison, MN — 30 mi; 5 — Summit, SD — 42 mi.SDMN25 mi · 40 km1. Canby, MN — 20 mi12. Watertown, SD — 25 mi23. Brookings, SD — 30 mi34. Madison, MN — 30 mi45. Summit, SD — 42 mi5
  1. Canby, MN 20 mi (33 km)
  2. Watertown, SD 25 mi (40 km)
  3. Brookings, SD 30 mi (49 km)
  4. Madison, MN 30 mi (49 km)
  5. Summit, 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: 44.7575, -96.6831.