U.S. Frost Dates by Weather Station

NOAA station USC00115493 · Illinois

Frost Dates near McHenry, IL

NOAA weather station McHenry – WG Stratton Lock and Dam (USC00115493), Illinois · elevation 736 ft (224 m) · hardiness zone 5b*

McHenry is the nearest town to the station (1.8 mi away) in GeoNames (CC BY 4.0). The dates below are measured at the station, not in the town itself.

  • Lower-risk planting dateafter May 19only 1 spring in 10 still has a frost later
  • Typical last frostMay 150% chance of a frost after it
  • Typical first fall frostOctober 1150% chance of a frost before it
  • Frost-free season162 daystypical year, 32°F
  • Hardiness zone5bcalculated*

The year at a glance

Frost season near McHenry, ILSpring: a frost after April 16 in 9 years out of 10, after May 1 in half of the years, after May 19 in 1 year out of 10. Fall: the first frost comes before September 27 in 1 year out of 10, before October 11 in half of the years, before October 24 in 9 years out of 10. Typical frost-free season: 162 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 1First frost ~Oct 11Frost season near McHenry, ILSpring: a frost after April 16 in 9 years out of 10, after May 1 in half of the years, after May 19 in 1 year out of 10. Fall: the first frost comes before September 27 in 1 year out of 10, before October 11 in half of the years, before October 24 in 9 years out of 10. Typical frost-free season: 162 days.JFMAMJJASONDLast frost ~May 1First frost ~Oct 11
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 26 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 19September 27
50% (typical)May 1October 11
90% (likely)April 16October 24
Frost-free season (32°F, 50% chance)
162 days
Hard frost (28°F), last in spring, 50% chance after
April 19
Hard frost (28°F), first in fall, 50% chance before
October 22

The last 15 years (2006–2020 normals)

Typical last frost April 30 (1 day earlier than the 30-year normal), typical first fall frost October 14 (3 days later). Frost-free season 166 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 near McHenry: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 19, 20% May 13, 30% May 8, 40% May 4, 50% May 1, 60% April 28, 70% April 25, 80% April 21, 90% April 16. Observed last spring frost in recent years: 2021 May 30, 2022 April 27, 2023 April 27, 2024 April 25, 2025 May 10, 2026 May 7.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 19May 1Apr 162021: May 302022: April 272023: April 272024: April 252025: May 102026: May 7Fall near McHenry: chance of a frost before this dateFall, chance of a frost before the date: 10% September 27, 20% October 2, 30% October 5, 40% October 9, 50% October 11, 60% October 14, 70% October 17, 80% October 20, 90% October 24. Observed first fall frost in recent years: 2021 October 22, 2022 October 8, 2023 October 11, 2024 October 16, 2025 October 24.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 27Oct 11Oct 242021: October 222022: October 82023: October 112024: October 162025: October 24
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 30October 22
2022April 27October 8
2023April 27October 11
2024April 25October 16
2025May 10October 24
2026May 7season not over yet

What these dates mean

Setting tender crops on the early spring date of April 16 in the McHenry area carries a 90 % chance that a light frost will occur later, so planting then is a gamble. The 50 % spring date of May 1 marks the point where the probability of a light frost is 50 %, indicating the median risk level for the 32 °F threshold.

In the fall, the 50 % date of October 11 marks the point where the probability of a light frost is 50 %, showing an even split in risk. Gardeners can use these median dates to gauge how the probability curve is centered without treating them as frost events themselves.

A cautious plan for tender crops uses the May 19 date (10 % chance of a later frost) in spring and the September 27 date (10 % chance of an earlier frost) in fall. Hard frost at 28 °F, shown by the April 19 and October 22 median dates, can damage plants more severely than 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 19" 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 27" 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 McHenry, ILNumbered nearest stations: 1 — Elgin, IL — 17 mi; 2 — Burlington, WI — 24 mi; 3 — Chicago Botanic Garden, IL — 27 mi; 4 — Chicago (O'Hare Airport), IL — 27 mi; 5 — Kenosha, WI — 28 mi.ILWIINMI25 mi · 40 km1. Elgin, IL — 17 mi12. Burlington, WI — 24 mi23. Chicago Botanic Garden, IL — 27 mi34. Chicago (O'Hare Airport), IL — 27 mi45. Kenosha, WI — 28 mi5
  1. Elgin, IL 17 mi (28 km)
  2. Burlington, WI 24 mi (38 km)
  3. Chicago Botanic Garden, IL 27 mi (43 km)
  4. Chicago (O'Hare Airport), IL 27 mi (44 km)
  5. Kenosha, WI 28 mi (46 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: 42.3092, -88.2533.