U.S. Frost Dates by Weather Station

NOAA station USC00486660 · Wyoming

Frost Dates for Newcastle, WY

NOAA weather station Newcastle (USC00486660), Wyoming · elevation 4415 ft (1346 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 26only 1 spring in 10 still has a frost later
  • Typical last frostMay 1350% chance of a frost after it
  • Typical first fall frostOctober 350% chance of a frost before it
  • Frost-free season143 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Newcastle, WYSpring: a frost after April 30 in 9 years out of 10, after May 13 in half of the years, after May 26 in 1 year out of 10. Fall: the first frost comes before September 17 in 1 year out of 10, before October 3 in half of the years, before October 16 in 9 years out of 10. Typical frost-free season: 143 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 13First frost ~Oct 3Frost season at Newcastle, WYSpring: a frost after April 30 in 9 years out of 10, after May 13 in half of the years, after May 26 in 1 year out of 10. Fall: the first frost comes before September 17 in 1 year out of 10, before October 3 in half of the years, before October 16 in 9 years out of 10. Typical frost-free season: 143 days.JFMAMJJASONDLast frost ~May 13First frost ~Oct 3
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 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 26September 17
50% (typical)May 13October 3
90% (likely)April 30October 16
Frost-free season (32°F, 50% chance)
143 days
Hard frost (28°F), last in spring, 50% chance after
May 1
Hard frost (28°F), first in fall, 50% chance before
October 11

The last 15 years (2006–2020 normals)

Typical last frost May 12 (1 day earlier than the 30-year normal), typical first fall frost October 6 (3 days later). Frost-free season 144 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 Newcastle: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 26, 20% May 21, 30% May 18, 40% May 15, 50% May 13, 60% May 10, 70% May 7, 80% May 4, 90% April 30. Observed last spring frost in recent years: 2021 May 11, 2022 May 22, 2023 May 1, 2024 May 7, 2025 May 2, 2026 May 19.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 26May 13Apr 302021: May 112022: May 222023: May 12024: May 72025: May 22026: May 19Fall at Newcastle: chance of a frost before this dateFall, chance of a frost before the date: 10% September 17, 20% September 23, 30% September 26, 40% September 30, 50% October 3, 60% October 5, 70% October 8, 80% October 11, 90% October 16. Observed first fall frost in recent years: 2021 October 13, 2022 October 17, 2023 October 8, 2024 October 25, 2025 October 14.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 17Oct 3Oct 162021: October 132022: October 172023: October 82024: October 252025: October 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. ◆ 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 11October 13
2022May 22October 17
2023May 1October 8
2024May 7October 25
2025May 2October 14
2026May 19season not over yet

What these dates mean

May 26 is the cautious spring date for light frost in Newcastle; with only a 10 % chance of a frost later than that date, a gardener can plan to set out tender crops.

The 50 % light-frost dates are May 13 and October 3; each holds a 50 % chance of a frost later (May 13) or earlier (October 3) than the date, providing a median reference point. The 50 % hard-frost dates are May 1 and October 11, marking when a frost of 28 °F is as likely as not. The cautious fall date is September 17, which has only a 10 % chance of a frost earlier than that date, allowing a gardener to finish harvesting tender crops.

Hard frost at 28 °F can damage plants that survive a light frost at 32 °F, so it represents a greater risk to tender crops.

How to read the probabilities

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

  • Spring: "10% after May 26" 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 17" 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 Newcastle, WYNumbered nearest stations: 1 — Upton, WY — 27 mi; 2 — Custer, SD — 29 mi; 3 — Hill City, SD — 32 mi; 4 — Mount Rushmore National Memorial, SD — 36 mi; 5 — near Colonial Pine Hills, SD — 38 mi.WY25 mi · 40 km1. Upton, WY — 27 mi12. Custer, SD — 29 mi23. Hill City, SD — 32 mi34. Mount Rushmore National Memorial, SD — 36 mi45. near Colonial Pine Hills, SD — 38 mi5
  1. Upton, WY 27 mi (43 km)
  2. Custer, SD 29 mi (47 km)
  3. Hill City, SD 32 mi (51 km)
  4. Mount Rushmore National Memorial, SD 36 mi (59 km)
  5. near Colonial Pine Hills, SD 38 mi (61 km)

Sources

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

Station coordinates: 43.8497, -104.1886.