U.S. Frost Dates by Weather Station

NOAA station USC00211074 · Minnesota

Frost Dates for Bruno, MN

NOAA weather station Bruno 7 ENE (USC00211074), Minnesota · elevation 1253 ft (382 m) · hardiness zone 4a*

  • Lower-risk planting dateafter June 1only 1 spring in 10 still has a frost later
  • Typical last frostMay 1850% chance of a frost after it
  • Typical first fall frostSeptember 2650% chance of a frost before it
  • Frost-free season129 daystypical year, 32°F
  • Hardiness zone4acalculated*

The year at a glance

Frost season at Bruno, MNSpring: a frost after May 3 in 9 years out of 10, after May 18 in half of the years, after June 1 in 1 year out of 10. Fall: the first frost comes before September 12 in 1 year out of 10, before September 26 in half of the years, before October 9 in 9 years out of 10. Typical frost-free season: 129 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 18First frost ~Sep 26Frost season at Bruno, MNSpring: a frost after May 3 in 9 years out of 10, after May 18 in half of the years, after June 1 in 1 year out of 10. Fall: the first frost comes before September 12 in 1 year out of 10, before September 26 in half of the years, before October 9 in 9 years out of 10. Typical frost-free season: 129 days.JFMAMJJASONDLast frost ~May 18First frost ~Sep 26
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)June 1September 12
50% (typical)May 18September 26
90% (likely)May 3October 9
Frost-free season (32°F, 50% chance)
129 days
Hard frost (28°F), last in spring, 50% chance after
May 5
Hard frost (28°F), first in fall, 50% chance before
October 5

The last 15 years (2006–2020 normals)

Typical last frost May 15 (3 days earlier than the 30-year normal), typical first fall frost September 29 (3 days later). Frost-free season 136 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 Bruno: chance of a frost after this dateSpring, chance of a frost after the date: 10% June 1, 20% May 28, 30% May 24, 40% May 21, 50% May 18, 60% May 16, 70% May 13, 80% May 9, 90% May 3. Observed last spring frost in recent years: 2021 May 29, 2022 May 5, 2023 May 4, 2024 April 26.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1Jun 1May 18May 32021: May 292022: May 52023: May 42024: April 26Fall at Bruno: chance of a frost before this dateFall, chance of a frost before the date: 10% September 12, 20% September 17, 30% September 21, 40% September 23, 50% September 26, 60% September 29, 70% October 1, 80% October 4, 90% October 9. Observed first fall frost in recent years: 2021 October 21, 2022 September 28, 2023 October 9, 2024 October 4.Fall: first frostChance of a frost before this date10%50%90%Sep 1Oct 1Sep 12Sep 26Oct 92021: October 212022: September 282023: October 92024: October 4
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 29October 21
2022May 5September 28
2023May 4October 9
2024April 26October 4
2025no datano data
2026no dataseason not over yet

What these dates mean

Setting out tender crops on May 3 in Bruno carries a 90% chance of a frost and is a gamble.

The 50% date is May 18, which marks a 50% chance of a frost later than this date, and the 50% date is September 26, which marks a 50% chance of a frost earlier than this date. For a cautious plan, tender crops are usually placed after the June 1 light-frost date, which has only a 10% chance of a later frost, and are harvested before the September 12 light-frost date, which likewise has a 10% chance of an earlier frost.

Hard frosts at 28 °F, reflected by the May 5 and October 5 50% dates, can damage vegetation more severely than the 32 °F light frosts, so they are a critical consideration for any planting schedule.

How to read the probabilities

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

  • Spring: "10% after June 1" 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 12" 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 Bruno, MNNumbered nearest stations: 1 — Moose Lake, MN — 14 mi; 2 — Cloquet, MN — 28 mi; 3 — Wright, MN — 33 mi; 4 — Gordon, WI — 35 mi; 5 — Superior, WI — 37 mi.25 mi · 40 km1. Moose Lake, MN — 14 mi12. Cloquet, MN — 28 mi23. Wright, MN — 33 mi34. Gordon, WI — 35 mi45. Superior, WI — 37 mi5
  1. Moose Lake, MN 14 mi (23 km)
  2. Cloquet, MN 28 mi (45 km)
  3. Wright, MN 33 mi (53 km)
  4. Gordon, WI 35 mi (56 km)
  5. Superior, WI 37 mi (59 km)

Sources

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

Station coordinates: 46.3003, -92.5336.