U.S. Frost Dates by Weather Station

NOAA station USW00094908 · Iowa

Frost Dates for Dubuque, IA

NOAA weather station Dubuque Regional Airport (USW00094908), Iowa · elevation 1056 ft (322 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 12only 1 spring in 10 still has a frost later
  • Typical last frostApril 2850% chance of a frost after it
  • Typical first fall frostOctober 1150% chance of a frost before it
  • Frost-free season165 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Dubuque, IASpring: a frost after April 13 in 9 years out of 10, after April 28 in half of the years, after May 12 in 1 year out of 10. Fall: the first frost comes before September 28 in 1 year out of 10, before October 11 in half of the years, before October 23 in 9 years out of 10. Typical frost-free season: 165 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 28First frost ~Oct 11Frost season at Dubuque, IASpring: a frost after April 13 in 9 years out of 10, after April 28 in half of the years, after May 12 in 1 year out of 10. Fall: the first frost comes before September 28 in 1 year out of 10, before October 11 in half of the years, before October 23 in 9 years out of 10. Typical frost-free season: 165 days.JFMAMJJASONDLast frost ~Apr 28First frost ~Oct 11
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 12September 28
50% (typical)April 28October 11
90% (likely)April 13October 23
Frost-free season (32°F, 50% chance)
165 days
Hard frost (28°F), last in spring, 50% chance after
April 17
Hard frost (28°F), first in fall, 50% chance before
October 21

The last 15 years (2006–2020 normals)

Typical last frost April 29 (1 day later than the 30-year normal), typical first fall frost October 13 (2 days later). Frost-free season 166 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 Dubuque: 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 1, 50% April 28, 60% April 25, 70% April 21, 80% April 18, 90% April 13. Observed last spring frost in recent years: 2021 April 25, 2022 April 27, 2023 April 26, 2024 April 21, 2025 April 16, 2026 May 7.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 12Apr 28Apr 132021: April 252022: April 272023: April 262024: April 212025: April 162026: May 7Fall at Dubuque: chance of a frost before this dateFall, chance of a frost before the date: 10% September 28, 20% October 2, 30% October 5, 40% October 8, 50% October 11, 60% October 13, 70% October 16, 80% October 19, 90% October 23. Observed first fall frost in recent years: 2021 October 22, 2022 October 8, 2023 October 10, 2024 October 16.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 28Oct 11Oct 232021: October 222022: October 82023: October 102024: October 16
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
2021April 25October 22
2022April 27October 8
2023April 26October 10
2024April 21October 16
2025April 16incomplete record
2026May 7season not over yet

What these dates mean

Setting out tender crops on the early spring date, April 13, is a gamble in Dubuque; there is a 90 % chance that a light frost will occur later than this date. Gardeners who prefer to limit risk wait until the cautious spring date, May 12, when only a 10 % chance of a later frost remains.

The 50 % date is April 28, meaning a 50 % chance of a light frost later than that day; the fall counterpart is October 11, with a 50 % chance of a frost earlier than that day. The cautious fall date, September 28, carries a 10 % chance that a frost has already arrived. Over the 30-year record, the two 32 °F 50 % dates are 165 days apart. Because Dubuque is in USDA hardiness zone 5a, these probabilities guide the timing of fragile crops. Hard frost at 28 °F is more damaging than a light frost, so the median hard-frost dates—April 17 and October 21—provide a key reference for the coldest conditions.

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 28" 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 Dubuque, IANumbered nearest stations: 1 — Dubuque Lock and Dam 11, IA — 10 mi; 2 — near Bellevue, IA — 17 mi; 3 — Cascade, IA — 17 mi; 4 — Maquoketa, IA — 22 mi; 5 — Lancaster, WI — 30 mi.IAWIIL25 mi · 40 km1. Dubuque Lock and Dam 11, IA — 10 mi12. near Bellevue, IA — 17 mi23. Cascade, IA — 17 mi34. Maquoketa, IA — 22 mi45. Lancaster, WI — 30 mi5
  1. Dubuque Lock and Dam 11, IA 10 mi (17 km)
  2. near Bellevue, IA 17 mi (28 km)
  3. Cascade, IA 17 mi (28 km)
  4. Maquoketa, IA 22 mi (36 km)
  5. Lancaster, WI 30 mi (48 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: 42.3978, -90.7036.