U.S. Frost Dates by Weather Station

NOAA station USC00057296 · Colorado

Frost Dates for Rustic, CO

NOAA weather station Rustic 9 WSW (USC00057296), Colorado · elevation 7700 ft (2347 m) · hardiness zone 5b*

  • Lower-risk planting dateafter June 20only 1 spring in 10 still has a frost later
  • Typical last frostJune 550% chance of a frost after it
  • Typical first fall frostSeptember 1650% chance of a frost before it
  • Frost-free season101 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Rustic, COSpring: a frost after May 24 in 9 years out of 10, after June 5 in half of the years, after June 20 in 1 year out of 10. Fall: the first frost comes before September 5 in 1 year out of 10, before September 16 in half of the years, before September 29 in 9 years out of 10. Typical frost-free season: 101 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Jun 5First frost ~Sep 16Frost season at Rustic, COSpring: a frost after May 24 in 9 years out of 10, after June 5 in half of the years, after June 20 in 1 year out of 10. Fall: the first frost comes before September 5 in 1 year out of 10, before September 16 in half of the years, before September 29 in 9 years out of 10. Typical frost-free season: 101 days.JFMAMJJASONDLast frost ~Jun 5First frost ~Sep 16
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)June 20September 5
50% (typical)June 5September 16
90% (likely)May 24September 29
Frost-free season (32°F, 50% chance)
101 days
Hard frost (28°F), last in spring, 50% chance after
May 22
Hard frost (28°F), first in fall, 50% chance before
September 26

The last 15 years (2006–2020 normals)

Typical last frost June 4 (1 day earlier than the 30-year normal), typical first fall frost September 14 (2 days earlier). Frost-free season 101 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 Rustic: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 20, 20% June 16, 30% June 11, 40% June 8, 50% June 5, 60% June 2, 70% May 31, 80% May 28, 90% May 24. Observed last spring frost in recent years: 2021 May 25, 2022 June 2, 2023 May 20, 2024 May 25, 2025 May 22, 2026 June 12.Spring: last frostChance of a frost after this date10%50%90%Jun 1Jul 1Jun 20Jun 5May 242021: May 252022: June 22023: May 202024: May 252025: May 222026: June 12Fall at Rustic: chance of a frost before this dateFall, chance of a frost before the date: 10% September 5, 20% September 8, 30% September 11, 40% September 14, 50% September 16, 60% September 19, 70% September 22, 80% September 24, 90% September 29. Observed first fall frost in recent years: 2021 September 21, 2022 October 7, 2023 October 7, 2024 September 20.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 5Sep 16Sep 292021: September 212022: October 72023: October 72024: September 20
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 25September 21
2022June 2October 7
2023May 20October 7
2024May 25September 20
2025May 22incomplete record
2026June 12season not over yet

What these dates mean

The cautious spring date in Rustic is June 20, when there is only a 10 % chance of a light frost occurring later, and it gives a gardener a reliable point to set out tender crops. The 50% date is June 5; at that point there is a 50 % chance of a light frost in spring, while the early spring gamble of May 24 carries a 90 % chance of frost.

The cautious fall date in Rustic is September 5, when there is only a 10 % chance of a light frost having arrived earlier, allowing a gardener to finish harvesting tender crops. The 50% date is September 16; at that point there is a 50 % chance of a light frost in fall. The 50% hard-frost date in spring is May 22 and the 50% hard-frost date in fall is September 26. Hard frost at 28 °F can damage plant tissue that usually survives a light frost at 32 °F.

How to read the probabilities

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

  • Spring: "10% after June 20" 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 5" 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 Rustic, CONumbered nearest stations: 1 — Fort Collins, CO — 34 mi; 2 — near Granby, CO — 37 mi; 3 — Fort Collins 4 E, CO — 37 mi; 4 — Loveland, CO — 38 mi; 5 — Laramie, WY — 42 mi.CONE25 mi · 40 km1. Fort Collins, CO — 34 mi12. near Granby, CO — 37 mi23. Fort Collins 4 E, CO — 37 mi34. Loveland, CO — 38 mi45. Laramie, WY — 42 mi5
  1. Fort Collins, CO 34 mi (55 km)
  2. near Granby, CO 37 mi (59 km)
  3. Fort Collins 4 E, CO 37 mi (60 km)
  4. Loveland, CO 38 mi (61 km)
  5. Laramie, WY 42 mi (68 km)

Sources

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

Station coordinates: 40.7022, -105.7106.