U.S. Frost Dates by Weather Station

NOAA station USW00014737 · Pennsylvania

Frost Dates for Allentown, PA

NOAA weather station Allentown International Airport (USW00014737), Pennsylvania · elevation 390 ft (119 m) · hardiness zone 7a*

  • Lower-risk planting dateafter May 6only 1 spring in 10 still has a frost later
  • Typical last frostApril 2050% chance of a frost after it
  • Typical first fall frostOctober 2450% chance of a frost before it
  • Frost-free season184 daystypical year, 32°F
  • Hardiness zone7acalculated*

The year at a glance

Frost season at Allentown, PASpring: a frost after April 6 in 9 years out of 10, after April 20 in half of the years, after May 6 in 1 year out of 10. Fall: the first frost comes before October 8 in 1 year out of 10, before October 24 in half of the years, before November 6 in 9 years out of 10. Typical frost-free season: 184 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 20First frost ~Oct 24Frost season at Allentown, PASpring: a frost after April 6 in 9 years out of 10, after April 20 in half of the years, after May 6 in 1 year out of 10. Fall: the first frost comes before October 8 in 1 year out of 10, before October 24 in half of the years, before November 6 in 9 years out of 10. Typical frost-free season: 184 days.JFMAMJJASONDLast frost ~Apr 20First frost ~Oct 24
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 30 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 6October 8
50% (typical)April 20October 24
90% (likely)April 6November 6
Frost-free season (32°F, 50% chance)
184 days
Hard frost (28°F), last in spring, 50% chance after
April 5
Hard frost (28°F), first in fall, 50% chance before
November 4

The last 15 years (2006–2020 normals)

Typical last frost April 20 (same as the 30-year normal), typical first fall frost October 27 (3 days later). Frost-free season 188 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 Allentown: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 6, 20% April 30, 30% April 26, 40% April 23, 50% April 20, 60% April 17, 70% April 14, 80% April 11, 90% April 6. Observed last spring frost in recent years: 2021 April 22, 2022 April 30, 2023 May 18, 2024 April 26, 2025 April 18, 2026 April 21.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 6Apr 20Apr 62021: April 222022: April 302023: May 182024: April 262025: April 182026: April 21Fall at Allentown: chance of a frost before this dateFall, chance of a frost before the date: 10% October 8, 20% October 13, 30% October 17, 40% October 21, 50% October 24, 60% October 27, 70% October 31, 80% November 2, 90% November 6. Observed first fall frost in recent years: 2021 November 3, 2022 October 19, 2023 November 1, 2024 October 17, 2025 October 10.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Oct 8Oct 24Nov 62021: November 32022: October 192023: November 12024: October 172025: 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
2021April 22November 3
2022April 30October 19
2023May 18November 1
2024April 26October 17
2025April 18October 10
2026April 21season not over yet

What these dates mean

Setting out tender crops on the early spring date, April 6, carries a 90 % chance of a frost later in Allentown, so it is a gamble. The cautious date for planting those crops is May 6, when only a 10 % chance of a light frost remains. In the fall, finishing tender crops after the cautious date of October 8 still leaves just a 10 % chance that a frost has arrived earlier.

The 50 % dates—April 20 for spring and October 24 for fall—mark the moment when the odds of a 32 °F light frost are equal; they are not frost events themselves but useful reference points for gardeners. Hard-frost dates, April 5 in spring and November 4 in fall, indicate when a 28 °F freeze is as likely as not, and a hard frost can damage plants that would otherwise survive a light frost. The record spans 30 years and the interval between the two 32 °F 50 % dates is 184 days.

How to read the probabilities

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

  • Spring: "10% after May 6" 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 8" 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 Allentown, PANumbered nearest stations: 1 — Hamburg, PA — 29 mi; 2 — Flemington, NJ — 30 mi; 3 — near Whitfield, PA — 36 mi; 4 — Phoenixville, PA — 37 mi; 5 — Wilkes-Barre, PA — 49 mi.PANJNY25 mi · 40 km1. Hamburg, PA — 29 mi12. Flemington, NJ — 30 mi23. near Whitfield, PA — 36 mi34. Phoenixville, PA — 37 mi45. Wilkes-Barre, PA — 49 mi5
  1. Hamburg, PA 29 mi (47 km)
  2. Flemington, NJ 30 mi (49 km)
  3. near Whitfield, PA 36 mi (57 km)
  4. Phoenixville, PA 37 mi (59 km)
  5. Wilkes-Barre, PA 49 mi (79 km)

Sources

* Hardiness zone 7a: zone derived from PRISM 2023 grid at the station location (not the official USDA map). Source data: PRISM Group, Oregon State University.

Station coordinates: 40.6508, -75.4492.