U.S. Frost Dates by Weather Station

NOAA station USC00115943 · Illinois

Frost Dates for Mount Vernon, IL

NOAA weather station Mount Vernon 3 NE (USC00115943), Illinois · elevation 490 ft (149 m) · hardiness zone 6b*

  • Lower-risk planting dateafter April 26only 1 spring in 10 still has a frost later
  • Typical last frostApril 1150% chance of a frost after it
  • Typical first fall frostOctober 2250% chance of a frost before it
  • Frost-free season193 daystypical year, 32°F
  • Hardiness zone6bcalculated*

The year at a glance

Frost season at Mount Vernon, ILSpring: a frost after March 30 in 9 years out of 10, after April 11 in half of the years, after April 26 in 1 year out of 10. Fall: the first frost comes before October 9 in 1 year out of 10, before October 22 in half of the years, before November 1 in 9 years out of 10. Typical frost-free season: 193 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 11First frost ~Oct 22Frost season at Mount Vernon, ILSpring: a frost after March 30 in 9 years out of 10, after April 11 in half of the years, after April 26 in 1 year out of 10. Fall: the first frost comes before October 9 in 1 year out of 10, before October 22 in half of the years, before November 1 in 9 years out of 10. Typical frost-free season: 193 days.JFMAMJJASONDLast frost ~Apr 11First frost ~Oct 22
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.Today

Frost dates (32°F)

Probability of frost, based on 28 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)April 26October 9
50% (typical)April 11October 22
90% (likely)March 30November 1
Frost-free season (32°F, 50% chance)
193 days
Hard frost (28°F), last in spring, 50% chance after
April 1
Hard frost (28°F), first in fall, 50% chance before
November 1

The last 15 years (2006–2020 normals)

Typical last frost April 10 (1 day earlier than the 30-year normal), typical first fall frost October 25 (3 days later). Frost-free season 196 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 Mount Vernon: chance of a frost after this dateSpring, chance of a frost after the date: 10% April 26, 20% April 21, 30% April 17, 40% April 14, 50% April 11, 60% April 8, 70% April 5, 80% April 2, 90% March 30. Observed last spring frost in recent years: 2021 April 21, 2023 April 24, 2024 April 22, 2025 April 12.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1Apr 26Apr 11Mar 302021: April 212023: April 242024: April 222025: April 12Fall at Mount Vernon: chance of a frost before this dateFall, chance of a frost before the date: 10% October 9, 20% October 14, 30% October 18, 40% October 20, 50% October 22, 60% October 25, 70% October 27, 80% October 29, 90% November 1. Observed first fall frost in recent years: 2021 November 2, 2022 October 8, 2023 October 30.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Oct 9Oct 22Nov 12021: November 22022: October 82023: October 30
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 21November 2
2022incomplete recordOctober 8
2023April 24October 30
2024April 22incomplete record
2025April 12incomplete record
2026incomplete recordseason not over yet

What these dates mean

Setting out tender crops on March 30 in Mount Vernon carries a 90% chance that a light frost will still occur later that spring, making it a gamble for growers seeking early emergence.

The 50% spring date, April 11, marks the point at which a light frost is equally likely to arrive later or not, while the 50% fall date, October 22, represents an even chance that a light frost has already arrived earlier. A cautious planting schedule therefore uses the April 26 date, which has only a 10% chance of a later frost, and the October 9 date, which has only a 10% chance that a frost has come earlier, to guide tender-crop timing.

Hard frost at 28°F can damage plants more severely than a 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 April 26" 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 9" 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 Mount Vernon, ILNumbered nearest stations: 1 — Salem, IL — 21 mi; 2 — Nashville, IL — 27 mi; 3 — near Fairfield, IL — 29 mi; 4 — near Carlyle, IL — 34 mi; 5 — Carmi, IL — 41 mi.IN25 mi · 40 km1. Salem, IL — 21 mi12. Nashville, IL — 27 mi23. near Fairfield, IL — 29 mi34. near Carlyle, IL — 34 mi45. Carmi, IL — 41 mi5
  1. Salem, IL 21 mi (33 km)
  2. Nashville, IL 27 mi (44 km)
  3. near Fairfield, IL 29 mi (46 km)
  4. near Carlyle, IL 34 mi (54 km)
  5. Carmi, IL 41 mi (66 km)

Sources

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

Station coordinates: 38.3483, -88.8533.