U.S. Frost Dates by Weather Station

NOAA station USC00050834 · Colorado

Frost Dates for Bonny Dam 2 NE, CO

NOAA weather station Bonny Dam 2 NE (USC00050834), Colorado · elevation 3717 ft (1133 m) · hardiness zone 6a*

  • Lower-risk planting dateafter May 19only 1 spring in 10 still has a frost later
  • Typical last frostMay 550% chance of a frost after it
  • Typical first fall frostOctober 1050% chance of a frost before it
  • Frost-free season155 daystypical year, 32°F
  • Hardiness zone6acalculated*

The year at a glance

Frost season at Bonny Dam 2 NE, COSpring: a frost after April 21 in 9 years out of 10, after May 5 in half of the years, after May 19 in 1 year out of 10. Fall: the first frost comes before September 28 in 1 year out of 10, before October 10 in half of the years, before October 21 in 9 years out of 10. Typical frost-free season: 155 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 5First frost ~Oct 10Frost season at Bonny Dam 2 NE, COSpring: a frost after April 21 in 9 years out of 10, after May 5 in half of the years, after May 19 in 1 year out of 10. Fall: the first frost comes before September 28 in 1 year out of 10, before October 10 in half of the years, before October 21 in 9 years out of 10. Typical frost-free season: 155 days.JFMAMJJASONDLast frost ~May 5First frost ~Oct 10
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 25 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 19September 28
50% (typical)May 5October 10
90% (likely)April 21October 21
Frost-free season (32°F, 50% chance)
155 days
Hard frost (28°F), last in spring, 50% chance after
April 25
Hard frost (28°F), first in fall, 50% chance before
October 18

The last 15 years (2006–2020 normals)

Typical last frost May 5 (same as the 30-year normal), typical first fall frost October 13 (3 days later). Frost-free season 159 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 Bonny Dam 2 NE: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 19, 20% May 14, 30% May 10, 40% May 8, 50% May 5, 60% May 2, 70% April 30, 80% April 26, 90% April 21. Observed last spring frost in recent years: 2021 April 26, 2022 May 22, 2023 April 29, 2024 April 22, 2026 May 6.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 19May 5Apr 212021: April 262022: May 222023: April 292024: April 222026: May 6Fall at Bonny Dam 2 NE: chance of a frost before this dateFall, chance of a frost before the date: 10% September 28, 20% October 2, 30% October 4, 40% October 7, 50% October 10, 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 25, 2025 October 19.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 28Oct 10Oct 212021: October 142022: October 172023: October 72024: October 252025: 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 26October 14
2022May 22October 17
2023April 29October 7
2024April 22October 25
2025incomplete recordOctober 19
2026May 6season not over yet

What these dates mean

May 19 is the cautious spring date for tender crops in Bonny Dam 2 NE, meaning there is only a 10 % chance of a light frost occurring later, so growers can plan to set out sensitive plants with relatively low risk.

The 50 % light-frost dates are May 5 in spring and October 10 in fall; each marks the point where a light frost is equally likely to have happened or not. The 50 % hard-frost dates are April 25 and October 18, indicating when a 28 °F frost is as probable as not. For a cautious schedule, the spring date May 19 is used to start tender crops, while September 28 serves as the cautious fall date to finish harvesting them before a light frost becomes more likely. A hard frost at 28 °F can injure 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 19" 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 28" 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 Bonny Dam 2 NE, CONumbered nearest stations: 1 — Saint Francis, KS — 18 mi; 2 — Burlington, CO — 25 mi; 3 — Wray, CO — 30 mi; 4 — Joes, CO — 30 mi; 5 — Goodland, KS — 30 mi.COKSNE25 mi · 40 km1. Saint Francis, KS — 18 mi12. Burlington, CO — 25 mi23. Wray, CO — 30 mi34. Joes, CO — 30 mi45. Goodland, KS — 30 mi5
  1. Saint Francis, KS 18 mi (29 km)
  2. Burlington, CO 25 mi (41 km)
  3. Wray, CO 30 mi (48 km)
  4. Joes, CO 30 mi (48 km)
  5. Goodland, KS 30 mi (48 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: 39.6567, -102.1192.