U.S. Frost Dates by Weather Station

NOAA station USC00365573 · Pennsylvania

Frost Dates for McKeesport, PA

NOAA weather station McKeesport (USC00365573), Pennsylvania · elevation 740 ft (226 m) · hardiness zone 6b*

  • Lower-risk planting dateafter May 20only 1 spring in 10 still has a frost later
  • Typical last frostMay 250% chance of a frost after it
  • Typical first fall frostOctober 2050% chance of a frost before it
  • Frost-free season170 daystypical year, 32°F
  • Hardiness zone6bcalculated*

The year at a glance

Frost season at McKeesport, PASpring: a frost after April 17 in 9 years out of 10, after May 2 in half of the years, after May 20 in 1 year out of 10. Fall: the first frost comes before October 1 in 1 year out of 10, before October 20 in half of the years, before November 3 in 9 years out of 10. Typical frost-free season: 170 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 2First frost ~Oct 20Frost season at McKeesport, PASpring: a frost after April 17 in 9 years out of 10, after May 2 in half of the years, after May 20 in 1 year out of 10. Fall: the first frost comes before October 1 in 1 year out of 10, before October 20 in half of the years, before November 3 in 9 years out of 10. Typical frost-free season: 170 days.JFMAMJJASONDLast frost ~May 2First frost ~Oct 20
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 25 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 20October 1
50% (typical)May 2October 20
90% (likely)April 17November 3
Frost-free season (32°F, 50% chance)
170 days
Hard frost (28°F), last in spring, 50% chance after
April 20
Hard frost (28°F), first in fall, 50% chance before
November 1

The last 15 years (2006–2020 normals)

Typical last frost April 30 (2 days earlier than the 30-year normal), typical first fall frost October 20. Frost-free season 167 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 McKeesport: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 20, 20% May 14, 30% May 10, 40% May 5, 50% May 2, 60% April 29, 70% April 26, 80% April 22, 90% April 17.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 20May 2Apr 17Fall at McKeesport: chance of a frost before this dateFall, chance of a frost before the date: 10% October 1, 20% October 6, 30% October 11, 40% October 15, 50% October 20, 60% October 24, 70% October 27, 80% October 31, 90% November 3.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Oct 1Oct 20Nov 3
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 170 days between the 50% light-frost dates—May 2 and October 20—contain the window in which tender garden crops can be grown at McKeesport without a 50 % chance of a light frost. For a gardener the May 2 and October 20 dates simply mark the points where the odds of a 32 °F frost are even; earlier in spring and later in fall the probability shifts sharply.

A cautious planting schedule therefore uses the May 20 date, which carries only a 10 % chance that a light frost will occur later, while a cautious harvest finish uses the October 1 date, which carries only a 10 % chance that a light frost will have arrived earlier. Planting on April 17 or extending a crop to November 3 would involve a 90 % chance of a light frost and is a gamble.

Hard frost dates—April 20 and November 1—are noted because 28 °F can damage plants that survive a light frost, making the colder threshold more critical.

How to read the probabilities

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

  • Spring: "10% after May 20" 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 McKeesport, PANumbered nearest stations: 1 — Salina, PA — 20 mi; 2 — Pittsburgh, PA — 21 mi; 3 — Uniontown, PA — 30 mi; 4 — near Ford City, PA — 32 mi; 5 — Waynesburg, PA — 34 mi.OHWVMD25 mi · 40 km1. Salina, PA — 20 mi12. Pittsburgh, PA — 21 mi23. Uniontown, PA — 30 mi34. near Ford City, PA — 32 mi45. Waynesburg, PA — 34 mi5
  1. Salina, PA 20 mi (33 km)
  2. Pittsburgh, PA 21 mi (34 km)
  3. Uniontown, PA 30 mi (49 km)
  4. near Ford City, PA 32 mi (51 km)
  5. Waynesburg, PA 34 mi (55 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: 40.3392, -79.8603.