U.S. Frost Dates by Weather Station

NOAA station USC00112500 · Illinois

Frost Dates for Dwight, IL

NOAA weather station Dwight (USC00112500), Illinois · elevation 628 ft (191 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 14only 1 spring in 10 still has a frost later
  • Typical last frostApril 2750% chance of a frost after it
  • Typical first fall frostOctober 1550% chance of a frost before it
  • Frost-free season170 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Dwight, ILSpring: a frost after April 14 in 9 years out of 10, after April 27 in half of the years, after May 14 in 1 year out of 10. Fall: the first frost comes before September 30 in 1 year out of 10, before October 15 in half of the years, before October 27 in 9 years out of 10. Typical frost-free season: 170 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 27First frost ~Oct 15Frost season at Dwight, ILSpring: a frost after April 14 in 9 years out of 10, after April 27 in half of the years, after May 14 in 1 year out of 10. Fall: the first frost comes before September 30 in 1 year out of 10, before October 15 in half of the years, before October 27 in 9 years out of 10. Typical frost-free season: 170 days.JFMAMJJASONDLast frost ~Apr 27First frost ~Oct 15
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 14September 30
50% (typical)April 27October 15
90% (likely)April 14October 27
Frost-free season (32°F, 50% chance)
170 days
Hard frost (28°F), last in spring, 50% chance after
April 17
Hard frost (28°F), first in fall, 50% chance before
October 25

The last 15 years (2006–2020 normals)

Typical last frost April 25 (2 days earlier than the 30-year normal), typical first fall frost October 19 (4 days later). Frost-free season 176 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 Dwight: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 14, 20% May 8, 30% May 3, 40% April 30, 50% April 27, 60% April 24, 70% April 21, 80% April 18, 90% April 14. Observed last spring frost in recent years: 2021 May 8, 2022 April 28, 2023 April 28, 2024 April 26, 2025 April 16, 2026 May 2.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 14Apr 27Apr 142021: May 82022: April 282023: April 282024: April 262025: April 162026: May 2Fall at Dwight: chance of a frost before this dateFall, chance of a frost before the date: 10% September 30, 20% October 5, 30% October 9, 40% October 12, 50% October 15, 60% October 17, 70% October 20, 80% October 23, 90% October 27. Observed first fall frost in recent years: 2022 October 8, 2023 October 30, 2024 October 16, 2025 October 23.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 30Oct 15Oct 272022: October 82023: October 302024: October 162025: 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
2021May 8incomplete record
2022April 28October 8
2023April 28October 30
2024April 26October 16
2025April 16October 23
2026May 2season not over yet

What these dates mean

In Dwight there are 170 days between the two 32°F 50% dates, from April 27 to October 15, and within that interval the risk of a light frost is roughly equal either side of each date. The median light-frost dates are April 27 and October 15, while the median hard-frost dates are April 17 and October 25. Those four dates mark the points at which a light or hard frost is as likely as not over the 30-year record.

The cautious spring date for setting out tender crops is May 14, when there is only a 10% chance a light frost will occur later. In the fall the cautious date to finish harvesting tender crops is September 30, with only a 10% chance a light frost has arrived earlier. A hard frost, defined at 28°F, can damage or kill plant tissue that often survives a 32°F light frost, making it a more critical concern for gardeners.

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 30" 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 Dwight, ILNumbered nearest stations: 1 — Pontiac, IL — 20 mi; 2 — near Kankakee, IL — 27 mi; 3 — Chenoa, IL — 30 mi; 4 — Ottawa, IL — 30 mi; 5 — near Joliet, IL — 32 mi.ILIN25 mi · 40 km1. Pontiac, IL — 20 mi12. near Kankakee, IL — 27 mi23. Chenoa, IL — 30 mi34. Ottawa, IL — 30 mi45. near Joliet, IL — 32 mi5
  1. Pontiac, IL 20 mi (32 km)
  2. near Kankakee, IL 27 mi (44 km)
  3. Chenoa, IL 30 mi (48 km)
  4. Ottawa, IL 30 mi (48 km)
  5. near Joliet, IL 32 mi (51 km)

Sources

* Hardiness zone 5b: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 41.1072, -88.4111.