U.S. Frost Dates by Weather Station

NOAA station USC00135952 · Iowa

Frost Dates for New Hampton, IA

NOAA weather station New Hampton (USC00135952), Iowa · elevation 1148 ft (350 m) · hardiness zone 5a*

  • Lower-risk planting dateafter May 14only 1 spring in 10 still has a frost later
  • Typical last frostMay 250% chance of a frost after it
  • Typical first fall frostOctober 550% chance of a frost before it
  • Frost-free season155 daystypical year, 32°F
  • Hardiness zone5acalculated*

The year at a glance

Frost season at New Hampton, IASpring: a frost after April 17 in 9 years out of 10, after May 2 in half of the years, after May 14 in 1 year out of 10. Fall: the first frost comes before September 23 in 1 year out of 10, before October 5 in half of the years, before October 18 in 9 years out of 10. Typical frost-free season: 155 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 2First frost ~Oct 5Frost season at New Hampton, IASpring: a frost after April 17 in 9 years out of 10, after May 2 in half of the years, after May 14 in 1 year out of 10. Fall: the first frost comes before September 23 in 1 year out of 10, before October 5 in half of the years, before October 18 in 9 years out of 10. Typical frost-free season: 155 days.JFMAMJJASONDLast frost ~May 2First 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 29 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 14September 23
50% (typical)May 2October 5
90% (likely)April 17October 18
Frost-free season (32°F, 50% chance)
155 days
Hard frost (28°F), last in spring, 50% chance after
April 20
Hard frost (28°F), first in fall, 50% chance before
October 15

The last 15 years (2006–2020 normals)

Typical last frost May 1 (1 day earlier than the 30-year normal), typical first fall frost October 12 (7 days later). Frost-free season 161 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 New Hampton: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 14, 20% May 9, 30% May 6, 40% May 4, 50% May 2, 60% April 29, 70% April 26, 80% April 22, 90% April 17. Observed last spring frost in recent years: 2021 April 26, 2023 May 4, 2024 April 24, 2025 April 17, 2026 May 7.Spring: last frostChance of a frost after this date10%50%90%May 1May 14May 2Apr 172021: April 262023: May 42024: April 242025: April 172026: May 7Fall at New Hampton: chance of a frost before this dateFall, chance of a frost before the date: 10% September 23, 20% September 27, 30% September 30, 40% October 2, 50% October 5, 60% October 8, 70% October 11, 80% October 14, 90% October 18. Observed first fall frost in recent years: 2021 October 22, 2022 October 8, 2023 October 10, 2024 October 15, 2025 October 23.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 23Oct 5Oct 182021: October 222022: October 82023: October 102024: October 152025: October 23
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 26October 22
2022incomplete recordOctober 8
2023May 4October 10
2024April 24October 15
2025April 17October 23
2026May 7season not over yet

What these dates mean

May 14 is the cautious spring date, with only a 10 % chance that a light frost will occur later; this lets a gardener plan to set out tender crops with minimal risk. The 50% date in spring is May 2, and there is a 50 % chance of a light frost later than this date. The hard-frost median for spring is April 20; a hard frost at 28 °F can damage plants more severely than a light frost at 32 °F.

In the fall, September 23 is the cautious date, offering a 10 % chance that a light frost will have arrived earlier, so it is the point to finish harvesting tender crops. The 50% date in fall is October 5, and there is a 50 % chance of a light frost earlier than this date. The hard-frost median for fall is October 15, marking the point when 28 °F frost becomes a greater threat than the milder 32 °F light frost.

How to read the probabilities

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

  • Spring: "10% after May 14" 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 New Hampton, IANumbered nearest stations: 1 — Tripoli, IA — 16 mi; 2 — Charles City, IA — 18 mi; 3 — Cresco, IA — 26 mi; 4 — Fayette, IA — 27 mi; 5 — Osage, IA — 30 mi.MNWI25 mi · 40 km1. Tripoli, IA — 16 mi12. Charles City, IA — 18 mi23. Cresco, IA — 26 mi34. Fayette, IA — 27 mi45. Osage, IA — 30 mi5
  1. Tripoli, IA 16 mi (26 km)
  2. Charles City, IA 18 mi (29 km)
  3. Cresco, IA 26 mi (42 km)
  4. Fayette, IA 27 mi (43 km)
  5. Osage, IA 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: 43.0453, -92.3122.