U.S. Frost Dates by Weather Station

NOAA station USC00119021 · Illinois

Frost Dates for Watseka, IL

NOAA weather station Watseka 2 NW (USC00119021), Illinois · elevation 620 ft (189 m) · hardiness zone 5b*

  • Lower-risk planting dateafter May 10only 1 spring in 10 still has a frost later
  • Typical last frostApril 2450% chance of a frost after it
  • Typical first fall frostOctober 1650% chance of a frost before it
  • Frost-free season174 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season at Watseka, ILSpring: a frost after April 10 in 9 years out of 10, after April 24 in half of the years, after May 10 in 1 year out of 10. Fall: the first frost comes before October 1 in 1 year out of 10, before October 16 in half of the years, before October 28 in 9 years out of 10. Typical frost-free season: 174 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 24First frost ~Oct 16Frost season at Watseka, ILSpring: a frost after April 10 in 9 years out of 10, after April 24 in half of the years, after May 10 in 1 year out of 10. Fall: the first frost comes before October 1 in 1 year out of 10, before October 16 in half of the years, before October 28 in 9 years out of 10. Typical frost-free season: 174 days.JFMAMJJASONDLast frost ~Apr 24First frost ~Oct 16
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 10October 1
50% (typical)April 24October 16
90% (likely)April 10October 28
Frost-free season (32°F, 50% chance)
174 days
Hard frost (28°F), last in spring, 50% chance after
April 12
Hard frost (28°F), first in fall, 50% chance before
October 26

The last 15 years (2006–2020 normals)

Typical last frost April 23 (1 day earlier than the 30-year normal), typical first fall frost October 20 (4 days later). Frost-free season 177 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 Watseka: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 10, 20% May 4, 30% April 30, 40% April 27, 50% April 24, 60% April 21, 70% April 18, 80% April 15, 90% April 10.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 10Apr 24Apr 10Fall at Watseka: chance of a frost before this dateFall, chance of a frost before the date: 10% October 1, 20% October 7, 30% October 10, 40% October 13, 50% October 16, 60% October 19, 70% October 21, 80% October 25, 90% October 28.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Oct 1Oct 16Oct 28
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

The cautious fall date in Watseka for finishing the harvest is October 1, when there is only a 10 % chance a light frost has arrived.

For a gardener, the 50 % light-frost dates are April 24 in spring and October 16 in fall; these are the median points where a frost is equally likely to have occurred, but they are not themselves frost dates. The 50 % hard-frost dates, when temperatures drop to 28 °F, are April 12 and October 26. The two 32 °F 50 % dates are 174 days apart, based on 27 years of record.

A cautious plan for tender crops would plant out after the spring cautious date of May 10 and aim to harvest by the fall cautious date of October 1; attempting to set out earlier or to keep tender crops later carries a 90 % risk of frost. A hard frost at 28 °F can damage plants that would survive a light frost at 32 °F.

How to read the probabilities

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

  • Spring: "10% after May 10" 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 Watseka, ILNumbered nearest stations: 1 — Hoopeston, IL — 23 mi; 2 — near Kankakee, IL — 25 mi; 3 — Rensselaer, IN — 32 mi; 4 — Lowell, IN — 37 mi; 5 — Rantoul, IL — 39 mi.ILIN25 mi · 40 km1. Hoopeston, IL — 23 mi12. near Kankakee, IL — 25 mi23. Rensselaer, IN — 32 mi34. Lowell, IN — 37 mi45. Rantoul, IL — 39 mi5
  1. Hoopeston, IL 23 mi (37 km)
  2. near Kankakee, IL 25 mi (39 km)
  3. Rensselaer, IN 32 mi (51 km)
  4. Lowell, IN 37 mi (59 km)
  5. Rantoul, IL 39 mi (64 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: 40.7942, -87.7544.