U.S. Frost Dates by Weather Station

NOAA station USC00132364 · Iowa

Frost Dates for Dubuque Lock and Dam 11, IA

NOAA weather station Dubuque Lock and Dam 11 (USC00132364), Iowa · elevation 620 ft (189 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 4only 1 spring in 10 still has a frost later
  • Typical last frostApril 1950% chance of a frost after it
  • Typical first fall frostOctober 2150% chance of a frost before it
  • Frost-free season184 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at Dubuque Lock and Dam 11, IASpring: a frost after April 4 in 9 years out of 10, after April 19 in half of the years, after May 4 in 1 year out of 10. Fall: the first frost comes before October 7 in 1 year out of 10, before October 21 in half of the years, before November 2 in 9 years out of 10. Typical frost-free season: 184 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 19First frost ~Oct 21Frost season at Dubuque Lock and Dam 11, IASpring: a frost after April 4 in 9 years out of 10, after April 19 in half of the years, after May 4 in 1 year out of 10. Fall: the first frost comes before October 7 in 1 year out of 10, before October 21 in half of the years, before November 2 in 9 years out of 10. Typical frost-free season: 184 days.JFMAMJJASONDLast frost ~Apr 19First frost ~Oct 21
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 4October 7
50% (typical)April 19October 21
90% (likely)April 4November 2
Frost-free season (32°F, 50% chance)
184 days
Hard frost (28°F), last in spring, 50% chance after
April 7
Hard frost (28°F), first in fall, 50% chance before
November 1

The last 15 years (2006–2020 normals)

Typical last frost April 19 (same as the 30-year normal), typical first fall frost October 25 (4 days later). Frost-free season 187 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 Lock and Dam 11: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 4, 20% April 30, 30% April 25, 40% April 22, 50% April 19, 60% April 16, 70% April 12, 80% April 9, 90% April 4. Observed last spring frost in recent years: 2021 April 23, 2022 April 27, 2023 April 25, 2024 April 22, 2025 April 9, 2026 April 8.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 4Apr 19Apr 42021: April 232022: April 272023: April 252024: April 222025: April 92026: April 8Fall at Dubuque Lock and Dam 11: chance of a frost before this dateFall, chance of a frost before the date: 10% October 7, 20% October 13, 30% October 16, 40% October 19, 50% October 21, 60% October 24, 70% October 27, 80% October 30, 90% November 2. Observed first fall frost in recent years: 2021 November 1, 2022 October 14, 2023 October 30, 2024 November 13, 2025 November 9.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Oct 7Oct 21Nov 22021: November 12022: October 142023: October 302024: November 132025: November 9
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 23November 1
2022April 27October 14
2023April 25October 30
2024April 22November 13
2025April 9November 9
2026April 8season not over yet

What these dates mean

The 184 days between the 50% dates in Dubuque Lock and Dam 11, April 19 and October 21, define the interval in which the chance of a light frost stays under fifty percent on either side of those dates. During that span, the risk of a light frost is lower than it is outside the interval, giving a broad window for gardening activities.

For a cautious spring schedule, May 4 is the date with only a ten percent chance that a light frost will still occur later, making it the preferred benchmark for setting out tender crops. In the fall, October 7 serves as the cautious date, carrying only a ten percent chance that a light frost has already arrived, and therefore marks the recommended latest planting for tender varieties.

Hard-frost events at 28 °F—represented by the 50% dates April 7 and November 1—can injure plants more severely than the milder 32 °F light frosts.

How to read the probabilities

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

  • Spring: "10% after May 4" 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 October 7" 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 Lock and Dam 11, IANumbered nearest stations: 1 — Dubuque, IA — 10 mi; 2 — Lancaster, WI — 21 mi; 3 — near Bellevue, IA — 22 mi; 4 — Cascade, IA — 25 mi; 5 — near Guttenberg, IA — 28 mi.IAWIIL25 mi · 40 km1. Dubuque, IA — 10 mi12. Lancaster, WI — 21 mi23. near Bellevue, IA — 22 mi34. Cascade, IA — 25 mi45. near Guttenberg, IA — 28 mi5
  1. Dubuque, IA 10 mi (17 km)
  2. Lancaster, WI 21 mi (34 km)
  3. near Bellevue, IA 22 mi (36 km)
  4. Cascade, IA 25 mi (40 km)
  5. near Guttenberg, IA 28 mi (46 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: 42.54, -90.6461.