U.S. Frost Dates by Weather Station

NOAA station USC00141699 · Kansas

Frost Dates for Colby, KS

NOAA weather station Colby 1 SW (USC00141699), Kansas · elevation 3170 ft (966 m) · hardiness zone 6a*

  • Lower-risk planting dateafter May 15only 1 spring in 10 still has a frost later
  • Typical last frostMay 250% chance of a frost after it
  • Typical first fall frostOctober 950% chance of a frost before it
  • Frost-free season156 daystypical year, 32°F
  • Hardiness zone6acalculated*

The year at a glance

Frost season at Colby, KSSpring: a frost after April 20 in 9 years out of 10, after May 2 in half of the years, after May 15 in 1 year out of 10. Fall: the first frost comes before September 26 in 1 year out of 10, before October 9 in half of the years, before October 21 in 9 years out of 10. Typical frost-free season: 156 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 2First frost ~Oct 9Frost season at Colby, KSSpring: a frost after April 20 in 9 years out of 10, after May 2 in half of the years, after May 15 in 1 year out of 10. Fall: the first frost comes before September 26 in 1 year out of 10, before October 9 in half of the years, before October 21 in 9 years out of 10. Typical frost-free season: 156 days.JFMAMJJASONDLast frost ~May 2First frost ~Oct 9
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 27 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 15September 26
50% (typical)May 2October 9
90% (likely)April 20October 21
Frost-free season (32°F, 50% chance)
156 days
Hard frost (28°F), last in spring, 50% chance after
April 23
Hard frost (28°F), first in fall, 50% chance before
October 18

The last 15 years (2006–2020 normals)

Typical last frost May 1 (1 day earlier than the 30-year normal), typical first fall frost October 12 (3 days later). Frost-free season 161 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 Colby: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 15, 20% May 11, 30% May 8, 40% May 5, 50% May 2, 60% April 30, 70% April 28, 80% April 25, 90% April 20. Observed last spring frost in recent years: 2021 April 25, 2022 April 26, 2023 April 29, 2024 April 21, 2025 May 3, 2026 May 2.Spring: last frostChance of a frost after this date10%50%90%May 1May 15May 2Apr 202021: April 252022: April 262023: April 292024: April 212025: May 32026: May 2Fall at Colby: chance of a frost before this dateFall, chance of a frost before the date: 10% September 26, 20% September 30, 30% October 3, 40% October 6, 50% October 9, 60% October 12, 70% October 14, 80% October 17, 90% October 21. Observed first fall frost in recent years: 2021 October 14, 2022 October 17, 2023 October 7, 2024 October 26, 2025 October 19.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 26Oct 9Oct 212021: October 142022: October 172023: October 72024: October 262025: October 19
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
2021April 25October 14
2022April 26October 17
2023April 29October 7
2024April 21October 26
2025May 3October 19
2026May 2season not over yet

What these dates mean

The 156 days between the 32°F 50% dates of May 2 and October 9 in Colby frame the period in which tender crops can be grown without a light frost. The 50% dates are median points with an even chance of a light frost occurring after the spring date or before the fall date, but they are not frost dates themselves.

For a cautious spring plan, gardeners should wait until the May 15 date, which carries only a 10% chance of a light frost later; planting on April 20 would be a gamble with a 90% chance of frost. In the fall, the cautious date to finish tender crops is September 26, when there is only a 10% chance that a light frost has arrived earlier, while October 21 would be a gamble with a 90% chance of frost.

A hard frost at 28°F can damage plants that survive a light frost, so the hard-frost median dates of April 23 and October 18 are especially important.

How to read the probabilities

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

  • Spring: "10% after May 15" 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 26" 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 Colby, KSNumbered nearest stations: 1 — Brewster, KS — 20 mi; 2 — Oakley, KS — 20 mi; 3 — Atwood, KS — 28 mi; 4 — Goodland, KS — 34 mi; 5 — Saint Francis, KS — 47 mi.CONE25 mi · 40 km1. Brewster, KS — 20 mi12. Oakley, KS — 20 mi23. Atwood, KS — 28 mi34. Goodland, KS — 34 mi45. Saint Francis, KS — 47 mi5
  1. Brewster, KS 20 mi (33 km)
  2. Oakley, KS 20 mi (33 km)
  3. Atwood, KS 28 mi (45 km)
  4. Goodland, KS 34 mi (54 km)
  5. Saint Francis, KS 47 mi (76 km)

Sources

* Hardiness zone 6a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 39.3925, -101.0689.