Bryn Mawr-Skyway has some of the coolest summers among U.S. towns
The coldest hours of a January night bottom out at 36° on average. A year here swings 42° from midwinter lows to midsummer highs. Winters are mild: January nights here are milder than in 83% of U.S. towns. Homes need heating from November to March, the months averaging under 50°.
A year in Bryn Mawr-Skyway at a glance
Each month’s typical high and low, and what it brings.
What stands out about Bryn Mawr-Skyway’s climate
Compared with towns across the U.S., with Bryn Mawr-Skyway’s place in Washington beside it.
What a year in Bryn Mawr-Skyway feels like
Typical highs and lows by season and by month, from NOAA’s 30-year normals.
About 248 frost-free days a year
In half of years the last 32° night comes by March 13 and the first by November 16. Frost and day counts come from NOAA’s station at Renton Muni Airport, 1.2 miles from the town’s center, 240 ft lower.
The 2023 USDA map puts Bryn Mawr-Skyway’s center in zone 9a: the coldest night of a typical winter, averaged over 1991–2020, reaches about 20°. Plant labels use the zone; frost dates tell you when to plant.
Freezing nights by month
Average nights at or below 32°
90° days by month
Average days at 90° or more
About 6 inches of snow a winter
Snow, measured at Seattle Tacoma International Airport, falls mostly in February. Precipitation (rain plus melted snow) adds up to 40 inches a year; November is the wettest month and July the driest. Rain or snow falls on about 156 days a year.
Rain + melted snow by month
Inches of water
Snowfall by month
Inches of snow
Heating and cooling a home in Bryn Mawr-Skyway
94% of the work is heating, so the furnace matters far more than the air conditioner. Months averaging under 55° run from October through April.
Degree days add up how far each day’s average falls below (heating) or rises above (cooling) 65° over a year. NOAA normals at Renton Muni Airport.
Living with Bryn Mawr-Skyway’s climate
What the numbers mean for a garden, a free afternoon and a bad-weather day.
248 frost-free days in zone 9a. The last frost comes by Mar 13 in half of years, so many gardeners wait a week or two past that to set out tomatoes. The first fall frost comes by Nov 16.
Months with highs of 62–84° and lows of 40° or more: May, June, July, August and September. 0.8 miles of trails are waiting.
Parks & trails →Of the yearly building losses FEMA expects in Bryn Mawr-Skyway from natural hazards, earthquakes are the largest share (75%); heat waves, cold waves, winter storms and ice storms together are 1%. Normals are averages; the hazards page covers the extremes.
Natural hazards →Bryn Mawr-Skyway and its neighbors
Every town next door is within a degree of Bryn Mawr-Skyway in January and July, closer than the 5 km grid can tell apart. Tap a town to see its climate.
Climates most like Bryn Mawr-Skyway’s, farther away
TownRatings’ own comparison of NOAA 1991–2020 normals, not a NOAA product: places of 5,000+ at least 150 miles away, one per state, closest on January low, July high, precipitation and snow.
| Town | Jan. low | July high | Precip. | Snow |
|---|---|---|---|---|
| Bryn Mawr-Skyway, WA | 36° | 77° | 40" | 6.3" |
| Wilsonville, OR | 36° | 82° | 40" | 1.0" |
| Fairfax, CA | 41° | 76° | 38" | 0.0" |
| Nantucket, MA | 26° | 76° | 44" | 25" |
| Brigantine, NJ | 28° | 83° | 45" | 10" |
Temperatures and rain come from NOAA’s 5 km grid, so each town gets its own value. Snow and frost-free days come from the nearest weather station, so neighbors often share them.
Warmer than it used to be
The last 30 years in Bryn Mawr-Skyway averaged 1.0° warmer than the 1900s. The biggest change is in January (+2.4°).
A smaller shift than in 77% of U.S. towns.
Change by month
The two periods overlap (1991–2000 is in both), which makes the gap a little smaller than it would be between separate periods.
How Bryn Mawr-Skyway compares
Against 12,954 U.S. towns of 2,500 or more (one per 5 km climate cell), with Bryn Mawr-Skyway’s place among Washington’s.
Bryn Mawr-Skyway weather by month
Highs, lows and precipitation from NOAA’s grid at Bryn Mawr-Skyway’s center; snow, wet days and snow on the ground from Seattle Tacoma International Airport. 1991–2020 normals.
| Month | High | Low | Rain + melt | Snow | Wet days | Snow on ground | 30-yr range |
|---|---|---|---|---|---|---|---|
| January | 48° | 36° | 5.6" | 1.8" | 19 | 1 | 38° – 46° |
| February | 50° | 36° | 3.9" | 2.2" | 16 | 1 | 36° – 49° |
| March | 54° | 38° | 4.3" | 0.4" | 17 | 0 | 42° – 51° |
| April | 60° | 42° | 3.3" | 0.0" | 15 | 0 | 46° – 56° |
| May | 66° | 48° | 2.1" | 0.0" | 11 | 0 | 52° – 61° |
| June | 71° | 52° | 1.6" | 0.0" | 9 | 0 | 58° – 67° |
| July | 77° | 56° | 0.7" | 0.0" | 5 | 0 | 62° – 71° |
| August | 77° | 56° | 1.0" | 0.0" | 5 | 0 | 63° – 70° |
| September | 71° | 52° | 1.7" | 0.0" | 8 | 0 | 59° – 65° |
| October | 61° | 45° | 4.0" | 0.0" | 14 | 0 | 50° – 58° |
| November | 52° | 39° | 6.1" | 0.2" | 18 | 0 | 41° – 50° |
| December | 47° | 36° | 5.7" | 1.7" | 18 | 1 | 37° – 45° |
| Year | 61° | 45° | 39.9" | 6.3" | 156 | 4 |
How much a month can swing
A normal is an average. February swings the most: from 1991 to 2020 its average ranged from 36° to 49°. September is the most reliable, staying within 7°.
Where Bryn Mawr-Skyway’s numbers come from
Normals are 30-year averages, not a forecast. How TownRatings reads climate data →
- Temperatures and precipitation: NOAA’s gridded 1991–2020 normals for the 5 km cell at Bryn Mawr-Skyway’s center.
- Snow: Seattle Tacoma International Airport.
- Frost, freezing nights, 90° and 100° days, heating and cooling: Renton Muni Airport, 1.2 miles from the town’s center, 240 ft lower; the nearest station that passes our checks for distance, height and agreement with the grid.
- Growing zone: USDA Plant Hardiness Zone Map, 2023. USDA Agricultural Research Service and PRISM Group, Oregon State University, prism.oregonstate.edu/phzm, accessed 8 Oct 2026.
- Then and now: NOAA’s gridded normals for 1901–2000 at the same cell.
- Storms and extremes: FEMA National Risk Index (expected annual losses to buildings).
Common questions about Bryn Mawr-Skyway’s climate
What is the weather like in Bryn Mawr-Skyway?
A typical July afternoon reaches 77°, a January night drops to 36°, and about 6 inches of snow falls in a normal winter. Milder January nights than 83% of U.S. towns; cooler July afternoons than 97% of U.S. towns.
How cold does it get in Bryn Mawr-Skyway in winter?
December nights average 36°. About 30 nights a year reach 32° or below. In the coldest December of the last 30 years the month averaged 37°.
How much snow does Bryn Mawr-Skyway get?
About 6.3 inches in a normal winter at Seattle Tacoma International Airport, most of it in February, with snow on the ground about 4 days a year.
How hot does it get in Bryn Mawr-Skyway?
July, with a typical high of 77° and a low of 56°. About 4 days a year reach 90° (Renton Muni Airport).
When is the first and last frost in Bryn Mawr-Skyway?
In half of years the last spring frost (32°) comes by March 13 and the first fall frost by November 16, about 248 frost-free days, at Renton Muni Airport.
What growing zone is Bryn Mawr-Skyway in?
Zone 9a on the 2023 USDA Plant Hardiness Zone Map: the coldest night of a typical winter reaches about 20°.
What is the best time of year to visit Bryn Mawr-Skyway?
By one simple rule (highs of 62–84° and lows of 40° or more), May, June, July, August and September. The rule is ours, not NOAA’s; the month table has the numbers to judge by.
Is Bryn Mawr-Skyway getting warmer?
Yes: 1991–2020 averaged 1.0° warmer than 1901–2000 on NOAA’s grid. A smaller shift than 77% of U.S. towns.
Neighbors talk weather
Gardens, snow, and the best days of the year in Bryn Mawr-Skyway.
Source: NOAA NCEI U.S. Climate Normals, 1991–2020 and 1901–2000; USDA/PRISM 2023 hardiness zones; FEMA National Risk Index. Today’s forecast: National Weather Service.