U.S. Frost Dates by Weather Station

NOAA station USC00053530 · Colorado

Frost Dates for Grant, CO

NOAA weather station Grant (USC00053530), Colorado · elevation 8675 ft (2644 m) · hardiness zone 5b*

  • Lower-risk planting dateafter June 30only 1 spring in 10 still has a frost later
  • Typical last frostJune 1550% chance of a frost after it
  • Typical first fall frostSeptember 950% chance of a frost before it
  • Frost-free season84 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Grant, COSpring: a frost after June 1 in 9 years out of 10, after June 15 in half of the years, after June 30 in 1 year out of 10. Fall: the first frost comes before August 26 in 1 year out of 10, before September 9 in half of the years, before September 22 in 9 years out of 10. Typical frost-free season: 84 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Jun 15First frost ~Sep 9Frost season at Grant, COSpring: a frost after June 1 in 9 years out of 10, after June 15 in half of the years, after June 30 in 1 year out of 10. Fall: the first frost comes before August 26 in 1 year out of 10, before September 9 in half of the years, before September 22 in 9 years out of 10. Typical frost-free season: 84 days.JFMAMJJASONDLast frost ~Jun 15First frost ~Sep 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)June 30August 26
50% (typical)June 15September 9
90% (likely)June 1September 22
Frost-free season (32°F, 50% chance)
84 days
Hard frost (28°F), last in spring, 50% chance after
May 30
Hard frost (28°F), first in fall, 50% chance before
September 22

The last 15 years (2006–2020 normals)

Typical last frost June 12 (3 days earlier than the 30-year normal), typical first fall frost September 13 (4 days later). Frost-free season 91 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 Grant: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 30, 20% June 24, 30% June 20, 40% June 18, 50% June 15, 60% June 12, 70% June 9, 80% June 6, 90% June 1. Observed last spring frost in recent years: 2021 June 1, 2022 June 15, 2023 June 24, 2024 May 31, 2025 May 27, 2026 May 24.Spring: last frostChance of a frost after this date10%50%90%Jun 1Jul 1Jun 30Jun 15Jun 12021: June 12022: June 152023: June 242024: May 312025: May 272026: May 24Fall at Grant: chance of a frost before this dateFall, chance of a frost before the date: 10% August 26, 20% August 31, 30% September 3, 40% September 6, 50% September 9, 60% September 11, 70% September 14, 80% September 17, 90% September 22. Observed first fall frost in recent years: 2021 September 21, 2022 September 13, 2023 September 16, 2024 September 19, 2025 September 17.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Aug 26Sep 9Sep 222021: September 212022: September 132023: September 162024: September 192025: September 17
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
2021June 1September 21
2022June 15September 13
2023June 24September 16
2024May 31September 19
2025May 27September 17
2026May 24season not over yet

What these dates mean

Grant enjoys a span of 84 days between the two 32°F 50% dates, June 15 and September 9, which marks the period where a light frost is equally likely to occur before or after each date. These dates are not frost dates themselves.

For tender crops, the cautious spring date is June 30, when there is only a 10 % chance of a light frost later; planting earlier on June 1 carries a 90 % chance and is a gamble. In fall, the cautious date to finish harvesting tender crops is August 26, with a 10 % chance of a light frost earlier; waiting until September 22 involves a 90 % chance and is risky. The median hard-frost dates are May 30 in spring and September 22 in fall; 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 June 30" 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 August 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 Grant, CONumbered nearest stations: 1 — Bailey, CO — 11 mi; 2 — Cabin Creek, CO — 14 mi; 3 — Georgetown, CO — 17 mi; 4 — Evergreen, CO — 23 mi; 5 — near Coal Creek, CO — 34 mi.25 mi · 40 km1. Bailey, CO — 11 mi12. Cabin Creek, CO — 14 mi23. Georgetown, CO — 17 mi34. Evergreen, CO — 23 mi45. near Coal Creek, CO — 34 mi5
  1. Bailey, CO 11 mi (18 km)
  2. Cabin Creek, CO 14 mi (22 km)
  3. Georgetown, CO 17 mi (27 km)
  4. Evergreen, CO 23 mi (37 km)
  5. near Coal Creek, CO 34 mi (55 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: 39.4608, -105.6786.