Last spring frost
Mar 13
Frost Dates for Bryn Mawr-Skyway, WA
First fall frost
Nov 16
Growing season
248 days
Hardiness zone
9a
In an average year around Bryn Mawr-Skyway, WA, the last spring frost (32°F) is about Mar 13 and the first fall frost is about Nov 16, giving roughly a 248-day growing season. To be safe most years, wait until Feb 19 before setting out tender plants.
Last spring frost
Dates the last frost of spring typically ends. Plant tender crops after the risk has passed for your comfort level.
| Frost intensity | Early (10%) | Average (50%) | Late (90%) |
|---|---|---|---|
| Light (36°F) | Apr 25 | Apr 6 | Mar 21 |
| Freeze (32°F) | Mar 31 | Mar 13 | Feb 19 |
| Hard (28°F) | Mar 6 | Feb 13 | Jan 1 |
| Severe (24°F) | Feb 22 | Jan 8 | Dec 3 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Apr 25 | Apr 18 | Apr 14 | Apr 10 | Apr 6 | Apr 2 | Mar 31 | Mar 26 | Mar 21 |
| 32°F | Mar 31 | Mar 25 | Mar 22 | Mar 18 | Mar 13 | Mar 8 | Mar 3 | Feb 27 | Feb 19 |
| 28°F | Mar 6 | Feb 28 | Feb 24 | Feb 18 | Feb 13 | Feb 8 | Jan 31 | Jan 15 | Jan 1 |
| 24°F | Feb 22 | Feb 14 | Feb 4 | Jan 22 | Jan 8 | Jan 1 | Dec 24 | Dec 14 | Dec 3 |
| 20°F | Feb 15 | Jan 30 | Jan 7 | Dec 30 | Dec 24 | Dec 14 | Dec 9 | Dec 4 | Nov 30 |
First fall frost
Dates the first frost of fall typically arrives. Count back by a crop's days-to-maturity to know your planting cutoff.
| Frost intensity | Early (10%) | Average (50%) | Late (90%) |
|---|---|---|---|
| Light (36°F) | Oct 17 | Oct 31 | Nov 17 |
| Freeze (32°F) | Oct 29 | Nov 16 | Dec 9 |
| Hard (28°F) | Nov 11 | Dec 6 | Jan 9 |
| Severe (24°F) | Nov 22 | Dec 19 | Feb 9 |
Show full probability table (all thresholds & percentiles)
| °F | 10% | 20% | 30% | 40% | 50% | 60% | 70% | 80% | 90% |
|---|---|---|---|---|---|---|---|---|---|
| 36°F | Oct 17 | Oct 22 | Oct 25 | Oct 28 | Oct 31 | Nov 1 | Nov 5 | Nov 10 | Nov 17 |
| 32°F | Oct 29 | Nov 2 | Nov 7 | Nov 11 | Nov 16 | Nov 20 | Nov 25 | Dec 1 | Dec 9 |
| 28°F | Nov 11 | Nov 19 | Nov 25 | Dec 1 | Dec 6 | Dec 13 | Dec 21 | Dec 29 | Jan 9 |
| 24°F | Nov 22 | Nov 29 | Dec 4 | Dec 9 | Dec 19 | Dec 27 | Jan 2 | Jan 17 | Feb 9 |
| 20°F | Nov 24 | Dec 1 | Dec 4 | Dec 8 | Dec 14 | Dec 24 | Dec 30 | Jan 20 | Feb 12 |
Growing season is measured at 32°F with about 50% probability. Hardiness zone from the 2023 USDA map; frost normals from NOAA 1991-2020.
Where this data comes from
@endif These dates are computed from the nearest official weather station with long-term records: Renton Muni Ap, Wa, about 1.5 miles away@if(!empty($station['elevation_ft'])), at 29 ft elevation. The further the station and the greater the elevation difference from your yard, the more your local frost timing can vary.
How we calculate these dates
Frost and freeze dates come from the NOAA 1991–2020 U.S. Climate Normals, the National Oceanic and Atmospheric Administration's 30-year averages for each weather station. A date shown at the 50% level is the median: in half of years the frost falls on or before it. The 10% and 90% columns show the early and late ends of the range, so you can plant on the odds you're comfortable with. These are long-term averages, not a forecast for this year - always check your local outlook before planting.
Source: NOAA National Centers for Environmental Information, 1991–2020 Climate Normals (public domain). Harman is not affiliated with or endorsed by NOAA.
Frequently asked questions
When is the last frost in Bryn Mawr-Skyway, WA?
On average, the last spring frost (32°F) around Bryn Mawr-Skyway, WA is about Mar 13. In cooler years it can run later, so for a safer bet many gardeners wait until Feb 19.
When is the first frost in the fall?
The first fall frost around Bryn Mawr-Skyway, WA typically arrives about Nov 16. Count back by a crop's days to maturity to find the latest date you can plant it.
When can I plant tomatoes and other tender crops?
Tender crops like tomatoes, peppers and basil are damaged by frost, so wait until the last spring frost has passed - around Mar 13 on average, or Feb 19 to be safe most years.
How long is the growing season here?
The frost-free growing season (between the last spring and first fall 32°F frost) is about 248 days in a typical year.
Are these dates a forecast for this year?
No. They are 30-year averages from the NOAA 1991–2020 Climate Normals, not a prediction for the current year. Use them for planning and always check your local weather forecast before planting or protecting crops.
Local weather for 98178 Planting calendar → Washington frost dates →
Data source: NOAA 1991–2020 Climate Normals · Page updated Aug 4, 2026