Ice dam risk in Williamsport, PA
Ice dams in Williamsport, PA: how often
10.0 dam days a winter
Moderate risk. On an ordinary house in Williamsport, conditions for an ice dam come on about 10.0 days in a normal winter, mostly in January and February.
Williamsport averages 33 inches of snow a year and about 38 days with snow on the ground. Plenty falls, but it tends to melt off between storms, which keeps the count lower than the snowfall suggests. That gap is why snowfall alone misleads.
What your attic does to that number in Williamsport
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 6.4 | Moderate |
| Typical, some insulation, not air-sealed | 10.0 | Moderate |
| Older or poorly insulated, warm attic | 14.5 | Moderate |
Sealing and insulating a typical attic takes out about 3.6 days a winter here. It does not move the risk band, but it shortens every dam. An older house with a warm attic should expect closer to 14.5 days.
Preventing ice dams on a Williamsport roof
- Air-seal the attic floor: the gaps around the hatch, light fixtures, plumbing stacks and the top plates of interior walls. This is the fix that removes the cause, and it usually costs less than a season of contractor ice removal.
- Rake the bottom three or four feet of roof after any storm that leaves more than about six inches, from the ground with a roof rake.
Which to spend on first: air sealing or heat cable.
Williamsport winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 8.7 | 13.5 | 4.2 |
| February | 8.6 | 11.9 | 3.2 |
| March | 5.7 | 4.4 | 0.7 |
| April | 0.8 | 0.1 | 0.0 |
| October | 0.1 | 0.1 | 0.0 |
| November | 1.6 | 0.9 | 0.1 |
| December | 7.1 | 7.5 | 1.8 |
Williamsport next to nearby towns
Williamsport ranks 26 of 68 Pennsylvania cities here for ice-dam days, behind St. Marys at 26.9 days.
- Bloomsburg, PA 34 mi, 10.7 days
- Berwick, PA 43 mi, 16.8 days
- State College, PA 53 mi, 12.5 days
- Nanticoke, PA 54 mi, 14.4 days
- Pottsville, PA 58 mi, 17.9 days
Where these numbers come from
NOAA 1991–2020 climate normals from Williamsport 2, 2.8 miles from Williamsport. 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.