U.S. Frost Dates by Weather Station

NOAA station USC00451400 · Washington

Frost Dates near Bridgeport, WA

NOAA weather station Chief Joseph Dam (USC00451400), Washington · elevation 834 ft (254 m) · hardiness zone 7a*

Bridgeport is the nearest town to the station (1.3 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 13only 1 spring in 10 still has a frost later
  • Typical last frostApril 2650% chance of a frost after it
  • Typical first fall frostOctober 1150% chance of a frost before it
  • Frost-free season167 daystypical year, 32°F
  • Hardiness zone7acalculated*

The year at a glance

Frost season near Bridgeport, WASpring: a frost after April 9 in 9 years out of 10, after April 26 in half of the years, after May 13 in 1 year out of 10. Fall: the first frost comes before September 30 in 1 year out of 10, before October 11 in half of the years, before October 27 in 9 years out of 10. Typical frost-free season: 167 days.JanFebMarAprMayJunJulAugSepOctNovDecLast frost ~Apr 26First frost ~Oct 11Frost season near Bridgeport, WASpring: a frost after April 9 in 9 years out of 10, after April 26 in half of the years, after May 13 in 1 year out of 10. Fall: the first frost comes before September 30 in 1 year out of 10, before October 11 in half of the years, before October 27 in 9 years out of 10. Typical frost-free season: 167 days.JFMAMJJASONDLast frost ~Apr 26First 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 27 years of NOAA records (1991–2020 normals)
ChanceLast frost in spring afterFirst frost in fall before
10% (unlikely)May 13September 30
50% (typical)April 26October 11
90% (likely)April 9October 27
Frost-free season (32°F, 50% chance)
167 days
Hard frost (28°F), last in spring, 50% chance after
April 9
Hard frost (28°F), first in fall, 50% chance before
October 23

The last 15 years (2006–2020 normals)

Typical last frost April 27 (1 day later than the 30-year normal), typical first fall frost October 12 (1 day later). Frost-free season 168 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 Bridgeport: chance of a frost after this dateSpring, chance of a frost after the date: 10% May 13, 20% May 7, 30% May 2, 40% April 30, 50% April 26, 60% April 23, 70% April 19, 80% April 14, 90% April 9.Spring: last frostChance of a frost after this date10%50%90%Apr 1May 1May 13Apr 26Apr 9Fall near Bridgeport: chance of a frost before this dateFall, chance of a frost before the date: 10% September 30, 20% October 3, 30% October 5, 40% October 8, 50% October 11, 60% October 15, 70% October 18, 80% October 21, 90% October 27.Fall: first frostChance of a frost before this date10%50%90%Oct 1Nov 1Sep 30Oct 11Oct 27
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 Bridgeport area has 167 days between the 32°F 50% dates, a span that can hold the full cycle of tender-crop planting, growth, and harvest. The 50% spring date of April 26 and the 50% fall date of October 11 each represent an even-odds moment; they are not frost thresholds but simply the median points in the historical record.

In spring, the cautious date for setting out tender crops is May 13, which carries only a 10 % chance of a later light frost, while planting on April 9 carries a 90 % chance and is a gamble. In fall, the cautious date to finish harvesting tender crops is September 30, with only a 10 % chance that a light frost has already arrived; waiting until October 27 bears a 90 % chance of a premature frost.

A hard frost at 28°F, noted by the median dates April 9 and October 23, 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 13" 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 30" 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 Bridgeport, WANumbered nearest stations: 1 — Chelan, WA — 20 mi; 2 — Coulee Dam, WA — 30 mi; 3 — near Entiat, WA — 37 mi; 4 — Winthrop, WA — 41 mi; 5 — Wilbur, WA — 46 mi.25 mi · 40 km1. Chelan, WA — 20 mi12. Coulee Dam, WA — 30 mi23. near Entiat, WA — 37 mi34. Winthrop, WA — 41 mi45. Wilbur, WA — 46 mi5
  1. Chelan, WA 20 mi (32 km)
  2. Coulee Dam, WA 30 mi (49 km)
  3. near Entiat, WA 37 mi (60 km)
  4. Winthrop, WA 41 mi (66 km)
  5. Wilbur, WA 46 mi (73 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: 47.9967, -119.6483.