Ice dam risk in Lewiston, ID
Ice dams in Lewiston, ID: how often
1.8 dam days a winter
Low risk. On an ordinary house in Lewiston, conditions for an ice dam come on about 1.8 days in a normal winter, mostly in December and January.
Lewiston averages 13 inches of snow a year and about 11 days with snow on the ground. Most of it comes and goes within a few days. The conditions that make a dam need all three at once: snow, cold at the eave and heat above it.
What your attic does to that number in Lewiston
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 1.4 | Low |
| Typical, some insulation, not air-sealed | 1.8 | Low |
| Older or poorly insulated, warm attic | 2.4 | Low |
The attic matters less in Lewiston than in colder towns: there are only 0.4 days a winter between a typical attic and a sealed one.
Preventing ice dams on a Lewiston roof
- Check the gutters before the first snow and clear them, so meltwater has somewhere to go. If you see icicles thicker than a finger along the eave after a storm, that is the early sign to look at the attic.
Snowy places are not always the worst: why snowfall misleads.
Lewiston winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 2.7 | 3.4 | 0.6 |
| February | 3.8 | 2.6 | 0.4 |
| March | 0.8 | 0.9 | 0.1 |
| November | 1.3 | 1.1 | 0.1 |
| December | 4.1 | 3.1 | 0.6 |
Lewiston next to nearby towns
Lewiston ranks 26 of 26 Idaho cities here for ice-dam days, behind Rexburg at 42.8 days.
- Moscow, ID 23 mi, 11.0 days
- Pullman, WA 25 mi, 10.8 days
- Walla Walla, WA 68 mi, 1.6 days
- Cheney, WA 81 mi, 13.0 days
- Liberty Lake, WA 88 mi, 13.0 days
Where these numbers come from
NOAA 1991–2020 climate normals from Lewiston Airport, 1.7 miles from Lewiston. 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.
- The nearest weather station sits at a noticeably different elevation from Lewiston, so the snow figures may run high or low for the town itself.