Ice dam risk in Portsmouth, OH
How often ice dams form in Portsmouth
4.8 dam days a winter
Low risk. On an ordinary house in Portsmouth, conditions for an ice dam come on about 4.8 days in a normal winter, mostly in February and January.
Portsmouth averages 21 inches of snow a year and about 21 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 Portsmouth
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 3.3 | Low |
| Typical, some insulation, not air-sealed | 4.8 | Low |
| Older or poorly insulated, warm attic | 6.7 | Moderate |
The attic matters less in Portsmouth than in colder towns: there are only 1.5 days a winter between a typical attic and a sealed one.
What to do about ice dams in Portsmouth
- 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.
Portsmouth winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 5.5 | 7.2 | 1.9 |
| February | 6.7 | 7.9 | 1.9 |
| March | 4.0 | 1.8 | 0.3 |
| April | 0.6 | 0.2 | 0.0 |
| November | 0.7 | 0.5 | 0.1 |
| December | 3.3 | 3.2 | 0.7 |
Portsmouth next to nearby towns
Portsmouth ranks 172 of 176 Ohio cities here for ice-dam days, behind Euclid at 24.8 days.
- Ironton, OH 21 mi, 1.5 days
- Ashland, KY 26 mi, 1.5 days
- Huntington, WV 37 mi, 1.4 days
- Chillicothe, OH 41 mi, 5.2 days
- Circleville, OH 59 mi, 5.2 days
Where these numbers come from
NOAA 1991–2020 climate normals from Warnock 2, 18.3 miles from Portsmouth. 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.