U.S. Frost Dates by Weather Station

NOAA station USC00137669 · Iowa

Frost Dates for Sidney, IA

NOAA weather station Sidney 1 SSE (USC00137669), Iowa · elevation 1140 ft (348 m) · hardiness zone 6a*

  • Lower-risk planting dateafter May 2only 1 spring in 10 still has a frost later
  • Typical last frostApril 1950% chance of a frost after it
  • Typical first fall frostOctober 1950% chance of a frost before it
  • Frost-free season182 daystypical year, 32°F
  • Hardiness zone6acalculated*

The year at a glance

Frost season at Sidney, IASpring: a frost after April 5 in 9 years out of 10, after April 19 in half of the years, after May 2 in 1 year out of 10. Fall: the first frost comes before October 1 in 1 year out of 10, before October 19 in half of the years, before October 31 in 9 years out of 10. Typical frost-free season: 182 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 19First frost ~Oct 19Frost season at Sidney, IASpring: a frost after April 5 in 9 years out of 10, after April 19 in half of the years, after May 2 in 1 year out of 10. Fall: the first frost comes before October 1 in 1 year out of 10, before October 19 in half of the years, before October 31 in 9 years out of 10. Typical frost-free season: 182 days.JFMAMJJASONDLast frost ~Apr 19First frost ~Oct 19
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 27 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 2October 1
50% (typical)April 19October 19
90% (likely)April 5October 31
Frost-free season (32°F, 50% chance)
182 days
Hard frost (28°F), last in spring, 50% chance after
April 9
Hard frost (28°F), first in fall, 50% chance before
October 29

The last 15 years (2006–2020 normals)

Typical last frost April 20 (1 day later than the 30-year normal), typical first fall frost October 21 (2 days later). Frost-free season 183 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 Sidney: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 2, 20% April 29, 30% April 25, 40% April 22, 50% April 19, 60% April 16, 70% April 13, 80% April 9, 90% April 5.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 2Apr 19Apr 5Fall at Sidney: chance of a frost before this dateFall, chance of a frost before the date: 10% October 1, 20% October 8, 30% October 13, 40% October 16, 50% October 19, 60% October 22, 70% October 24, 80% October 27, 90% October 31.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Oct 1Oct 19Oct 31
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.

What these dates mean

182 days separate the two 32 °F 50% dates in Sidney, marking the interval in which most tender gardening activities can be scheduled. The median spring light-frost date is April 19 and the median fall light-frost date is October 19; these dates represent the point where a frost is equally likely to occur later or earlier, but they are not themselves frost dates.

Gardeners who prefer a cautious approach would wait until the May 2 light-frost date, which carries only a 10 % chance of a later frost, before setting out tender crops in spring. In the autumn, the equally cautious date is October 1, when there is only a 10 % chance that a frost has already arrived, making it the appropriate point to finish harvesting tender crops.

A hard frost at 28 °F can injure plants that would survive a light frost at 32 °F, so the 50% hard-frost dates of April 9 and October 29 are important reference points.

How to read the probabilities

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

  • Spring: "10% after May 2" 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 1" 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 Sidney, IANumbered nearest stations: 1 — Nebraska City, NE — 13 mi; 2 — Shenandoah, IA — 15 mi; 3 — Auburn, NE — 26 mi; 4 — Red Oak, IA — 28 mi; 5 — Syracuse, NE — 29 mi.NEIAMO25 mi · 40 km1. Nebraska City, NE — 13 mi12. Shenandoah, IA — 15 mi23. Auburn, NE — 26 mi34. Red Oak, IA — 28 mi45. Syracuse, NE — 29 mi5
  1. Nebraska City, NE 13 mi (21 km)
  2. Shenandoah, IA 15 mi (24 km)
  3. Auburn, NE 26 mi (42 km)
  4. Red Oak, IA 28 mi (45 km)
  5. Syracuse, NE 29 mi (47 km)

Sources

* Hardiness zone 6a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 40.7361, -95.6431.