U.S. Frost Dates by Weather Station

NOAA station USC00212881 · Minnesota

Frost Dates for Forest Lake, MN

NOAA weather station Forest Lake 5 NE (USC00212881), Minnesota · elevation 905 ft (276 m) · hardiness zone 4b*

  • Lower-risk planting dateafter May 19only 1 spring in 10 still has a frost later
  • Typical last frostMay 350% chance of a frost after it
  • Typical first fall frostOctober 550% chance of a frost before it
  • Frost-free season154 daystypical year, 32°F
  • Hardiness zone4bcalculated*

The year at a glance

Frost season at Forest Lake, MNSpring: a frost after April 20 in 9 years out of 10, after May 3 in half of the years, after May 19 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 20 in 9 years out of 10. Typical frost-free season: 154 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 3First frost ~Oct 5Frost season at Forest Lake, MNSpring: a frost after April 20 in 9 years out of 10, after May 3 in half of the years, after May 19 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 20 in 9 years out of 10. Typical frost-free season: 154 days.JFMAMJJASONDLast frost ~May 3First 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 28 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 19September 22
50% (typical)May 3October 5
90% (likely)April 20October 20
Frost-free season (32°F, 50% chance)
154 days
Hard frost (28°F), last in spring, 50% chance after
April 24
Hard frost (28°F), first in fall, 50% chance before
October 17

The last 15 years (2006–2020 normals)

Typical last frost May 1 (2 days earlier than the 30-year normal), typical first fall frost October 14 (9 days later). Frost-free season 164 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 Forest Lake: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 19, 20% May 13, 30% May 9, 40% May 6, 50% May 3, 60% May 1, 70% April 29, 80% April 25, 90% April 20. Observed last spring frost in recent years: 2021 May 11, 2022 April 28, 2024 April 25, 2025 April 19.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 19May 3Apr 202021: May 112022: April 282024: April 252025: April 19Fall at Forest Lake: chance of a frost before this dateFall, chance of a frost before the date: 10% September 22, 20% September 27, 30% September 30, 40% October 3, 50% October 5, 60% October 8, 70% October 12, 80% October 16, 90% October 20. Observed first fall frost in recent years: 2021 October 22, 2022 September 28, 2023 October 28, 2024 October 14, 2025 October 8.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 22Oct 5Oct 202021: October 222022: September 282023: October 282024: October 142025: 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
2023incomplete recordOctober 28
2024April 25October 14
2025April 19October 8
2026incomplete recordseason not over yet

What these dates mean

May 19 is the cautious spring date for light frost (32 °F) in Forest Lake, and it lets a gardener plan to set out tender crops with only a 10 % chance of a later frost.

The 50% dates—May 3 in spring and October 5 in fall—represent the median point when a light frost is equally likely to have occurred or not; they give a sense of the central timing of frost risk. For a cautious fall schedule the September 22 date, which carries a 10 % chance that a frost has already arrived, marks when tender crops should be finished harvesting. The hard-frost median dates are April 24 and October 17, and a hard frost at 28 °F can damage plants even when a light frost at 32 °F does not.

The span between the two 32 °F 50% dates, May 3 and October 5, is 154 days, based on 28 years of record, giving a sense of the length of the frost-free window. Gardeners can use these reference points when timing planting and harvest.

How to read the probabilities

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

  • Spring: "10% after May 19" 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 Forest Lake, MNNumbered nearest stations: 1 — St. Croix Falls, WI — 13 mi; 2 — Wild River State Park, MN — 15 mi; 3 — Luck, WI — 26 mi; 4 — Amery, WI — 26 mi; 5 — near Roseville, MN — 27 mi.MNWI25 mi · 40 km1. St. Croix Falls, WI — 13 mi12. Wild River State Park, MN — 15 mi23. Luck, WI — 26 mi34. Amery, WI — 26 mi45. near Roseville, MN — 27 mi5
  1. St. Croix Falls, WI 13 mi (22 km)
  2. Wild River State Park, MN 15 mi (24 km)
  3. Luck, WI 26 mi (42 km)
  4. Amery, WI 26 mi (42 km)
  5. near Roseville, MN 27 mi (44 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: 45.3317, -92.8983.