U.S. Frost Dates by Weather Station

NOAA station USC00217107 · Minnesota

Frost Dates for Rosemount, MN

NOAA weather station Rosemount Research & Outreach Center (USC00217107), Minnesota · elevation 945 ft (288 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 16only 1 spring in 10 still has a frost later
  • Typical last frostMay 250% chance of a frost after it
  • Typical first fall frostOctober 550% chance of a frost before it
  • Frost-free season155 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Rosemount, MNSpring: a frost after April 19 in 9 years out of 10, after May 2 in half of the years, after May 16 in 1 year out of 10. Fall: the first frost comes before September 22 in 1 year out of 10, before October 5 in half of the years, before October 19 in 9 years out of 10. Typical frost-free season: 155 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 2First frost ~Oct 5Frost season at Rosemount, MNSpring: a frost after April 19 in 9 years out of 10, after May 2 in half of the years, after May 16 in 1 year out of 10. Fall: the first frost comes before September 22 in 1 year out of 10, before October 5 in half of the years, before October 19 in 9 years out of 10. Typical frost-free season: 155 days.JFMAMJJASONDLast frost ~May 2First frost ~Oct 5
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 16September 22
50% (typical)May 2October 5
90% (likely)April 19October 19
Frost-free season (32°F, 50% chance)
155 days
Hard frost (28°F), last in spring, 50% chance after
April 22
Hard frost (28°F), first in fall, 50% chance before
October 17

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 (7 days later). Frost-free season 162 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 Rosemount: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 16, 20% May 11, 30% May 8, 40% May 5, 50% May 2, 60% April 30, 70% April 27, 80% April 23, 90% April 19. Observed last spring frost in recent years: 2021 May 11, 2022 April 28, 2023 May 3, 2024 April 24, 2025 April 20, 2026 May 8.Spring: last frostChance of a frost after this date10%50%90%May 1May 16May 2Apr 192021: May 112022: April 282023: May 32024: April 242025: April 202026: May 8Fall at Rosemount: chance of a frost before this dateFall, chance of a frost before the date: 10% September 22, 20% September 28, 30% October 1, 40% October 3, 50% October 5, 60% October 9, 70% October 12, 80% October 15, 90% October 19. Observed first fall frost in recent years: 2021 October 22, 2022 September 28, 2023 October 11, 2024 October 15, 2025 October 8.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 22Oct 5Oct 192021: October 222022: September 282023: October 112024: October 152025: October 8
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 22
2022April 28September 28
2023May 3October 11
2024April 24October 15
2025April 20October 8
2026May 8season not over yet

What these dates mean

Rosemount enjoys a 155-day span between the two 32 °F 50 % dates, May 2 and October 5, providing the window for most garden activities.

For light frost the 50 % dates mark the point where a frost is equally likely to occur later (spring) or earlier (fall). The cautious spring date is May 16, when there is only a 10 % chance of a frost later, so tender crops are usually set out then. The cautious fall date is September 22, with only a 10 % chance that a frost has come earlier, making it a useful point to finish harvesting tender crops. Planting on April 19 in spring or extending to October 19 in fall carries a 90 % chance of frost and is a gamble.

The 50 % hard-frost dates are April 22 in spring and October 17 in fall, and a hard frost (28 °F) matters more because it can damage plants that survive a light frost (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 May 16" 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 22" 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 Rosemount, MNNumbered nearest stations: 1 — near Hastings, MN — 12 mi; 2 — Minneapolis (Minneapolis/St. Paul Airport), MN — 13 mi; 3 — near Roseville, MN — 19 mi; 4 — Lower St. Anthony Falls, MN — 19 mi; 5 — New Hope, MN — 24 mi.MNWI25 mi · 40 km1. near Hastings, MN — 12 mi12. Minneapolis (Minneapolis/St. Paul Airport), MN — 13 mi23. near Roseville, MN — 19 mi34. Lower St. Anthony Falls, MN — 19 mi45. New Hope, MN — 24 mi5
  1. near Hastings, MN 12 mi (19 km)
  2. Minneapolis (Minneapolis/St. Paul Airport), MN 13 mi (21 km)
  3. near Roseville, MN 19 mi (31 km)
  4. Lower St. Anthony Falls, MN 19 mi (31 km)
  5. New Hope, MN 24 mi (39 km)

Sources

* Hardiness zone 4b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 44.7167, -93.0981.