U.S. Frost Dates by Weather Station

NOAA station USC00210157 · Minnesota

Frost Dates for Amboy, MN

NOAA weather station Amboy (USC00210157), Minnesota · elevation 1030 ft (314 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 12only 1 spring in 10 still has a frost later
  • Typical last frostApril 3050% chance of a frost after it
  • Typical first fall frostOctober 750% chance of a frost before it
  • Frost-free season161 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Amboy, MNSpring: a frost after April 14 in 9 years out of 10, after April 30 in half of the years, after May 12 in 1 year out of 10. Fall: the first frost comes before September 23 in 1 year out of 10, before October 7 in half of the years, before October 22 in 9 years out of 10. Typical frost-free season: 161 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 30First frost ~Oct 7Frost season at Amboy, MNSpring: a frost after April 14 in 9 years out of 10, after April 30 in half of the years, after May 12 in 1 year out of 10. Fall: the first frost comes before September 23 in 1 year out of 10, before October 7 in half of the years, before October 22 in 9 years out of 10. Typical frost-free season: 161 days.JFMAMJJASONDLast frost ~Apr 30First frost ~Oct 7
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 26 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 12September 23
50% (typical)April 30October 7
90% (likely)April 14October 22
Frost-free season (32°F, 50% chance)
161 days
Hard frost (28°F), last in spring, 50% chance after
April 20
Hard frost (28°F), first in fall, 50% chance before
October 20

The last 15 years (2006–2020 normals)

Typical last frost April 27 (3 days earlier than the 30-year normal), typical first fall frost October 10 (3 days later). Frost-free season 165 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 Amboy: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 12, 20% May 7, 30% May 4, 40% May 2, 50% April 30, 60% April 27, 70% April 24, 80% April 20, 90% April 14.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 12Apr 30Apr 14Fall at Amboy: chance of a frost before this dateFall, chance of a frost before the date: 10% September 23, 20% September 28, 30% October 1, 40% October 4, 50% October 7, 60% October 11, 70% October 14, 80% October 18, 90% October 22.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 23Oct 7Oct 22
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.

What these dates mean

Setting out tender crops on April 14 in Amboy is a gamble, because there is a 90 % chance of a light frost later that season. Gardeners who prefer a lower risk wait until the cautious date of May 12, when only a 10 % chance of a light frost remains.

April 30 is the 50% date for light frost in spring, meaning there is a 50 % chance of a frost later than that day. In fall, October 7 serves as the 50% date, giving a 50 % chance of a frost earlier than that day, and the period between the two 32 °F 50% dates spans 161 days. For a cautious plan, the early-season date to set out tender crops is May 12, while the late-season date to finish harvesting tender crops is September 23, which carries only a 10 % chance of a frost earlier.

A hard frost at 28 °F (April 20 in spring and October 20 in fall) can damage plants that survive a 32 °F light frost, so it matters more.

How to read the probabilities

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

  • Spring: "10% after May 12" 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 23" 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 Amboy, MNNumbered nearest stations: 1 — Winnebago, MN — 8 mi; 2 — Saint James, MN — 23 mi; 3 — St. Peter, MN — 32 mi; 4 — near Waseca, MN — 34 mi; 5 — Estherville, IA — 44 mi.MNIA25 mi · 40 km1. Winnebago, MN — 8 mi12. Saint James, MN — 23 mi23. St. Peter, MN — 32 mi34. near Waseca, MN — 34 mi45. Estherville, IA — 44 mi5
  1. Winnebago, MN 8 mi (13 km)
  2. Saint James, MN 23 mi (38 km)
  3. St. Peter, MN 32 mi (51 km)
  4. near Waseca, MN 34 mi (55 km)
  5. Estherville, IA 44 mi (71 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: 43.8836, -94.1664.