U.S. Frost Dates by Weather Station

NOAA station USC00237398 · Missouri

Frost Dates for St. Charles, MO

NOAA weather station St. Charles 7 SSW (USC00237398), Missouri · elevation 450 ft (137 m) · hardiness zone 6b*

  • Lower-risk planting dateafter April 21only 1 spring in 10 still has a frost later
  • Typical last frostApril 450% chance of a frost after it
  • Typical first fall frostOctober 2950% chance of a frost before it
  • Frost-free season206 daystypical year, 32°F
  • Hardiness zone6bcalculated*

The year at a glance

Frost season at St. Charles, MOSpring: a frost after March 20 in 9 years out of 10, after April 4 in half of the years, after April 21 in 1 year out of 10. Fall: the first frost comes before October 15 in 1 year out of 10, before October 29 in half of the years, before November 11 in 9 years out of 10. Typical frost-free season: 206 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 4First frost ~Oct 29Frost season at St. Charles, MOSpring: a frost after March 20 in 9 years out of 10, after April 4 in half of the years, after April 21 in 1 year out of 10. Fall: the first frost comes before October 15 in 1 year out of 10, before October 29 in half of the years, before November 11 in 9 years out of 10. Typical frost-free season: 206 days.JFMAMJJASONDLast frost ~Apr 4First frost ~Oct 29
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 28 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)April 21October 15
50% (typical)April 4October 29
90% (likely)March 20November 11
Frost-free season (32°F, 50% chance)
206 days
Hard frost (28°F), last in spring, 50% chance after
March 25
Hard frost (28°F), first in fall, 50% chance before
November 8

The last 15 years (2006–2020 normals)

Typical last frost April 6 (2 days later than the 30-year normal), typical first fall frost October 29. Frost-free season 207 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 St. Charles: chance of a frost after this dateSpring, chance of a frost after the date: 10% April 21, 20% April 14, 30% April 10, 40% April 7, 50% April 4, 60% April 2, 70% March 31, 80% March 27, 90% March 20. Observed last spring frost in recent years: 2021 April 21, 2022 April 19, 2023 March 30, 2024 March 29, 2025 April 8, 2026 March 28.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1Apr 21Apr 4Mar 202021: April 212022: April 192023: March 302024: March 292025: April 82026: March 28Fall at St. Charles: chance of a frost before this dateFall, chance of a frost before the date: 10% October 15, 20% October 20, 30% October 24, 40% October 27, 50% October 29, 60% October 31, 70% November 2, 80% November 6, 90% November 11. Observed first fall frost in recent years: 2021 November 4, 2022 October 18, 2023 October 30, 2024 November 26, 2025 November 10.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Dec 1Oct 15Oct 29Nov 112021: November 42022: October 182023: October 302024: November 262025: November 10
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 4
2022April 19October 18
2023March 30October 30
2024March 29November 26
2025April 8November 10
2026March 28season not over yet

What these dates mean

The 206 days between the 50% dates in St. Charles, April 4 and October 29, define the period in which a light frost (32 °F) is equally likely to have occurred or not.

For a gardener, the April 4 median marks the point where the chance of a light frost later in spring is 50 %, while the October 29 median marks the point where the chance of a light frost earlier in fall is 50 %. A cautious plan uses April 21, which carries a 10 % chance of a later light frost, as the date to set out tender crops, and October 15, which carries a 10 % chance of an earlier light frost, as the date to finish harvesting them. By contrast, March 20 (90 % chance of a later light frost) and November 11 (90 % chance of an earlier light frost) represent gambles. The hard-frost 28 °F median dates are March 25 in spring and November 8 in fall.

A hard frost at 28 °F can injure plants that survive a 32 °F light frost, making it the more critical threat.

How to read the probabilities

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

  • Spring: "10% after April 21" 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 15" 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 St. Charles, MONumbered nearest stations: 1 — St. Louis (Spirit of St. Louis Airport), MO — 7 mi; 2 — near Weldon Spring, MO — 9 mi; 3 — Jerseyville, IL — 30 mi; 4 — Festus, MO — 32 mi; 5 — Elsberry, MO — 35 mi.MOIL25 mi · 40 km1. St. Louis (Spirit of St. Louis Airport), MO — 7 mi12. near Weldon Spring, MO — 9 mi23. Jerseyville, IL — 30 mi34. Festus, MO — 32 mi45. Elsberry, MO — 35 mi5
  1. St. Louis (Spirit of St. Louis Airport), MO 7 mi (12 km)
  2. near Weldon Spring, MO 9 mi (14 km)
  3. Jerseyville, IL 30 mi (49 km)
  4. Festus, MO 32 mi (52 km)
  5. Elsberry, MO 35 mi (57 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: 38.6853, -90.5233.