Ice dam risk in Mount Vernon, IL
Will your roof get ice dams in Mount Vernon, IL?
2.8 dam days a winter
Low risk. On an ordinary house in Mount Vernon, conditions for an ice dam come on about 2.8 days in a normal winter, mostly in January and February.
Mount Vernon averages 10 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 Mount Vernon
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 1.8 | Low |
| Typical, some insulation, not air-sealed | 2.8 | Low |
| Older or poorly insulated, warm attic | 4.1 | Low |
The attic matters less in Mount Vernon than in colder towns: there are only 1.0 day a winter between a typical attic and a sealed one.
Preventing ice dams on a Mount Vernon 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.
Mount Vernon winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 3.2 | 4.7 | 1.4 |
| February | 3.1 | 3.1 | 0.7 |
| March | 1.0 | 0.7 | 0.1 |
| October | 0.2 | 0.1 | 0.0 |
| November | 0.4 | 0.4 | 0.0 |
| December | 2.5 | 2.4 | 0.6 |
Mount Vernon next to nearby towns
Mount Vernon ranks 216 of 225 Illinois cities here for ice-dam days, behind Arlington Heights at 21.5 days.
- Centralia, IL 18 mi, 4.1 days
- Herrin, IL 36 mi, 3.1 days
- Marion, IL 40 mi, 3.1 days
- Carbondale, IL 44 mi, 2.3 days
- Highland, IL 52 mi, 2.5 days
Where these numbers come from
NOAA 1991–2020 climate normals from Mt Vernon 3 NE, 4.5 miles from Mount Vernon. 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.