U.S. Frost Dates by Weather Station

NOAA station USC00361139 · Pennsylvania

Frost Dates for Butler, PA

NOAA weather station Butler 2 SW (USC00361139), Pennsylvania · elevation 1000 ft (305 m) · hardiness zone 6b*

  • Lower-risk planting dateafter May 23only 1 spring in 10 still has a frost later
  • Typical last frostMay 750% chance of a frost after it
  • Typical first fall frostOctober 1450% chance of a frost before it
  • Frost-free season159 daystypical year, 32°F
  • Hardiness zone6bcalculated*

The year at a glance

Frost season at Butler, PASpring: a frost after April 22 in 9 years out of 10, after May 7 in half of the years, after May 23 in 1 year out of 10. Fall: the first frost comes before October 1 in 1 year out of 10, before October 14 in half of the years, before October 30 in 9 years out of 10. Typical frost-free season: 159 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 7First frost ~Oct 14Frost season at Butler, PASpring: a frost after April 22 in 9 years out of 10, after May 7 in half of the years, after May 23 in 1 year out of 10. Fall: the first frost comes before October 1 in 1 year out of 10, before October 14 in half of the years, before October 30 in 9 years out of 10. Typical frost-free season: 159 days.JFMAMJJASONDLast frost ~May 7First frost ~Oct 14
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 23October 1
50% (typical)May 7October 14
90% (likely)April 22October 30
Frost-free season (32°F, 50% chance)
159 days
Hard frost (28°F), last in spring, 50% chance after
April 26
Hard frost (28°F), first in fall, 50% chance before
October 27

The last 15 years (2006–2020 normals)

Typical last frost May 8 (1 day later than the 30-year normal), typical first fall frost October 19 (5 days later). Frost-free season 162 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 Butler: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 23, 20% May 19, 30% May 14, 40% May 10, 50% May 7, 60% May 3, 70% April 30, 80% April 27, 90% April 22.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 23May 7Apr 22Fall at Butler: chance of a frost before this dateFall, chance of a frost before the date: 10% October 1, 20% October 5, 30% October 8, 40% October 11, 50% October 14, 60% October 17, 70% October 20, 80% October 24, 90% October 30.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Oct 1Oct 14Oct 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.

What these dates mean

Setting out tender crops on April 22 in Butler is a gamble, because a frost later than that date occurs 90% of the time according to the 26-year record.

The cautious date for tender crops in spring is May 23, when there is only a 10% chance of a later frost; the 50% date is May 7, meaning a 50% chance of a frost later than that date. In the fall, the cautious date to finish harvesting tender crops is October 1, with a 10% chance of an earlier frost, while the 50% date is October 14. The 50% hard-frost dates are April 26 in spring and October 27 in fall, marking the midpoint of 28 °F risk.

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

How to read the probabilities

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

  • Spring: "10% after May 23" 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 Butler, PANumbered nearest stations: 1 — Slippery Rock, PA — 17 mi; 2 — near Ford City, PA — 23 mi; 3 — New Castle, PA — 26 mi; 4 — near Industry, PA — 28 mi; 5 — Pittsburgh, PA — 29 mi.OHWV25 mi · 40 km1. Slippery Rock, PA — 17 mi12. near Ford City, PA — 23 mi23. New Castle, PA — 26 mi34. near Industry, PA — 28 mi45. Pittsburgh, PA — 29 mi5
  1. Slippery Rock, PA 17 mi (27 km)
  2. near Ford City, PA 23 mi (37 km)
  3. New Castle, PA 26 mi (42 km)
  4. near Industry, PA 28 mi (45 km)
  5. Pittsburgh, PA 29 mi (47 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: 40.8414, -79.9164.