Ice dam risk in Mercer Island, WA
Will your roof get ice dams in Mercer Island, WA?
0.1 dam days a winter
Almost never. An ordinary house in Mercer Island sees 0.1 days a winter when an ice dam can form, because snow rarely stays on a roof long enough below freezing.
Mercer Island averages 4 inches of snow a year and about 2 days with snow on the ground. Too little lies on the roof for long. The conditions that make a dam need all three at once: snow, cold at the eave and heat above it.
Do you need to do anything in Mercer Island?
- Nothing for ice dams. If you are buying here and an inspector mentions water at the eaves, ask what they saw: it is far more likely a gutter, flashing or drip-edge problem than ice.
Snowy places are not always the worst: why snowfall misleads.
Mercer Island winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 0.9 | 0.5 | 0.0 |
| February | 1.0 | 0.6 | 0.0 |
| November | 0.2 | 0.2 | 0.0 |
| December | 1.7 | 0.9 | 0.1 |
Mercer Island next to nearby towns
Mercer Island ranks 77 of 91 Washington cities here for ice-dam days, behind Spokane at 13.0 days.
- Newcastle, WA 4 mi, 0.2 days
- Bellevue, WA 4 mi, 0.1 days
- Renton, WA 6 mi, 0.2 days
- Tukwila, WA 6 mi, 0.2 days
- Seattle, WA 7 mi, 0.1 days
Where these numbers come from
NOAA 1991–2020 climate normals from Seattle Sand Pt Wfo, 8.6 miles from Mercer Island. A dam day is a day with snow on the roof and freezing at the eave while heat or sun melts the snow above it. This describes a normal winter, not this one.