U.S. Frost Dates by Weather Station

NOAA station USC00368184 · Pennsylvania

Frost Dates for Slippery Rock, PA

NOAA weather station Slippery Rock 1 SSW (USC00368184), Pennsylvania · elevation 1260 ft (384 m) · hardiness zone 6a*

  • Lower-risk planting dateafter May 25only 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 season158 daystypical year, 32°F
  • Hardiness zone6acalculated*

The year at a glance

Frost season at Slippery Rock, PASpring: a frost after April 22 in 9 years out of 10, after May 7 in half of the years, after May 25 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: 158 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~May 7First frost ~Oct 14Frost season at Slippery Rock, PASpring: a frost after April 22 in 9 years out of 10, after May 7 in half of the years, after May 25 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: 158 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 27 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 25October 1
50% (typical)May 7October 14
90% (likely)April 22October 30
Frost-free season (32°F, 50% chance)
158 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 6 (1 day earlier 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 Slippery Rock: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 25, 20% May 19, 30% May 15, 40% May 11, 50% May 7, 60% May 3, 70% April 30, 80% April 27, 90% April 22. Observed last spring frost in recent years: 2021 May 14, 2022 April 30, 2023 April 27, 2024 April 26, 2025 April 18, 2026 May 13.Spring: last frostChance of a frost after this date10%50%90%May 1Jun 1May 25May 7Apr 222021: May 142022: April 302023: April 272024: April 262025: April 182026: May 13Fall at Slippery Rock: chance of a frost before this dateFall, chance of a frost before the date: 10% October 1, 20% October 4, 30% October 7, 40% October 10, 50% October 14, 60% October 16, 70% October 20, 80% October 24, 90% October 30. Observed first fall frost in recent years: 2021 November 2, 2023 October 23, 2025 October 10.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Oct 1Oct 14Oct 302021: November 22023: October 232025: October 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
2021May 14November 2
2022April 30incomplete record
2023April 27October 23
2024April 26incomplete record
2025April 18October 10
2026May 13season not over yet

What these dates mean

October 1 marks the cautious fall date for finishing the harvest in Slippery Rock; there is only a 10 % chance that a light frost has arrived before that day. In spring, the cautious date for setting out tender crops is May 25, when the chance of a light frost later than the date is just 10 %; planting earlier on April 22 carries a 90 % chance of a frost and is a gamble. The median light-frost dates are May 7 and October 14; a gardener faces a 50 % chance of a frost later than May 7 in spring and a 50 % chance of a frost earlier than October 14 in fall. Hard frost at 28°F, reflected by the 50 % dates of April 26 and October 27, can injure plants more severely than the lighter 32°F frost, so it is a more critical threshold for tender crops.

How to read the probabilities

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

  • Spring: "10% after May 25" 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 Slippery Rock, PANumbered nearest stations: 1 — New Castle, PA — 16 mi; 2 — Butler, PA — 17 mi; 3 — Franklin, PA — 27 mi; 4 — near Industry, PA — 33 mi; 5 — Youngstown, OH — 35 mi.PAOH25 mi · 40 km1. New Castle, PA — 16 mi12. Butler, PA — 17 mi23. Franklin, PA — 27 mi34. near Industry, PA — 33 mi45. Youngstown, OH — 35 mi5
  1. New Castle, PA 16 mi (26 km)
  2. Butler, PA 17 mi (27 km)
  3. Franklin, PA 27 mi (43 km)
  4. near Industry, PA 33 mi (53 km)
  5. Youngstown, OH 35 mi (56 km)

Sources

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

Station coordinates: 41.0561, -80.0594.