Ice dam risk in Norristown, PA
Ice dams in Norristown, PA: how often
3.3 dam days a winter
Low risk. On an ordinary house in Norristown, conditions for an ice dam come on about 3.3 days in a normal winter, mostly in February and January.
Norristown averages 25 inches of snow a year and about 15 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 Norristown
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 2.6 | Low |
| Typical, some insulation, not air-sealed | 3.3 | Low |
| Older or poorly insulated, warm attic | 4.3 | Low |
The attic matters less in Norristown than in colder towns: there are only 0.7 days a winter between a typical attic and a sealed one.
What to do about ice dams in Norristown
- 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.
Norristown winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 6.8 | 4.3 | 1.1 |
| February | 10.9 | 5.5 | 1.3 |
| March | 3.0 | 2.1 | 0.3 |
| April | 0.2 | 0.1 | 0.0 |
| October | 0.1 | 0.0 | 0.0 |
| November | 0.1 | 0.1 | 0.0 |
| December | 4.2 | 2.7 | 0.6 |
Norristown next to nearby towns
Norristown ranks 63 of 68 Pennsylvania cities here for ice-dam days, behind St. Marys at 26.9 days.
- Lansdale, PA 9 mi, 4.6 days
- Phoenixville, PA 10 mi, 8.7 days
- Lansdowne, PA 13 mi, 3.0 days
- Philadelphia, PA 13 mi, 2.3 days
- Yeadon, PA 14 mi, 3.0 days
Where these numbers come from
NOAA 1991–2020 climate normals from Norristown, 0.9 miles from Norristown. 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.
- Snow-on-the-ground counts come from a second, nearby station, because the closest one does not record them.