U.S. Frost Dates by Weather Station

NOAA station USC00214546 · Minnesota

Frost Dates for Lamberton SW Research & Outreach C, MN

NOAA weather station Lamberton SW Research & Outreach C (USC00214546), Minnesota · elevation 1140 ft (348 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 15only 1 spring in 10 still has a frost later
  • Typical last frostMay 350% chance of a frost after it
  • Typical first fall frostOctober 250% chance of a frost before it
  • Frost-free season152 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Lamberton SW Research & Outreach C, MNSpring: a frost after April 19 in 9 years out of 10, after May 3 in half of the years, after May 15 in 1 year out of 10. Fall: the first frost comes before September 18 in 1 year out of 10, before October 2 in half of the years, before October 16 in 9 years out of 10. Typical frost-free season: 152 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 3First frost ~Oct 2Frost season at Lamberton SW Research & Outreach C, MNSpring: a frost after April 19 in 9 years out of 10, after May 3 in half of the years, after May 15 in 1 year out of 10. Fall: the first frost comes before September 18 in 1 year out of 10, before October 2 in half of the years, before October 16 in 9 years out of 10. Typical frost-free season: 152 days.JFMAMJJASONDLast frost ~May 3First frost ~Oct 2
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 30 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 15September 18
50% (typical)May 3October 2
90% (likely)April 19October 16
Frost-free season (32°F, 50% chance)
152 days
Hard frost (28°F), last in spring, 50% chance after
April 24
Hard frost (28°F), first in fall, 50% chance before
October 13

The last 15 years (2006–2020 normals)

Typical last frost May 2 (1 day earlier than the 30-year normal), typical first fall frost October 7 (5 days later). Frost-free season 157 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 Lamberton SW Research & Outreach C: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 15, 20% May 11, 30% May 8, 40% May 5, 50% May 3, 60% May 1, 70% April 29, 80% April 25, 90% April 19. Observed last spring frost in recent years: 2021 May 12, 2022 May 4, 2023 April 26, 2024 April 24, 2025 May 3, 2026 May 20.Spring: last frostChance of a frost after this date10%50%90%May 1May 15May 3Apr 192021: May 122022: May 42023: April 262024: April 242025: May 32026: May 20Fall at Lamberton SW Research & Outreach C: chance of a frost before this dateFall, chance of a frost before the date: 10% September 18, 20% September 24, 30% September 27, 40% September 30, 50% October 2, 60% October 5, 70% October 8, 80% October 11, 90% October 16. Observed first fall frost in recent years: 2021 October 16, 2022 September 28, 2023 October 10, 2024 October 4, 2025 October 8.Fall: first frostChance of a frost before this date10%50%90%Oct 1Sep 18Oct 2Oct 162021: October 162022: September 282023: October 102024: October 42025: 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 12October 16
2022May 4September 28
2023April 26October 10
2024April 24October 4
2025May 3October 8
2026May 20season not over yet

What these dates mean

The 152 days between the 50% dates in Lamberton SW Research & Outreach C define the period when a light frost is as likely to occur as not, with May 3 marking the median point in spring and October 2 the median point in fall. For a gardener this means that around the middle of this span there is an even chance of a 32 °F frost arriving later in spring or having arrived earlier in fall.

The cautious spring date for setting out tender crops is May 15, which carries only a 10 % chance of a later frost, while the cautious fall date to finish harvesting tender crops is September 18, which carries only a 10 % chance that a frost has arrived earlier. A hard frost at 28 °F is more damaging because it reaches a lower temperature that can freeze plant tissue that would survive a 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 15" 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 18" 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 Lamberton SW Research & Outreach C, MNNumbered nearest stations: 1 — Tracy, MN — 16 mi; 2 — Redwood Falls, MN — 24 mi; 3 — Windom, MN — 27 mi; 4 — Marshall, MN — 28 mi; 5 — Lake Wilson, MN — 36 mi.SDIA25 mi · 40 km1. Tracy, MN — 16 mi12. Redwood Falls, MN — 24 mi23. Windom, MN — 27 mi34. Marshall, MN — 28 mi45. Lake Wilson, MN — 36 mi5
  1. Tracy, MN 16 mi (25 km)
  2. Redwood Falls, MN 24 mi (39 km)
  3. Windom, MN 27 mi (43 km)
  4. Marshall, MN 28 mi (46 km)
  5. Lake Wilson, MN 36 mi (57 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: 44.2394, -95.3153.