Ice dam risk in St. Charles, MO
How often ice dams form in St. Charles
4.1 dam days a winter
Low risk. On an ordinary house in St. Charles, conditions for an ice dam come on about 4.1 days in a normal winter, mostly in January and February.
St. Charles averages 9 inches of snow a year and about 17 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 St. Charles
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 2.7 | Low |
| Typical, some insulation, not air-sealed | 4.1 | Low |
| Older or poorly insulated, warm attic | 5.9 | Moderate |
The attic matters less in St. Charles than in colder towns: there are only 1.4 days a winter between a typical attic and a sealed one.
Preventing ice dams on a St. Charles 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.
St. Charles winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 4.3 | 6.1 | 1.8 |
| February | 2.6 | 5.2 | 1.2 |
| March | 0.5 | 1.4 | 0.2 |
| November | 0.1 | 0.6 | 0.1 |
| December | 1.5 | 3.8 | 0.9 |
St. Charles next to nearby towns
St. Charles ranks 28 of 80 Missouri cities here for ice-dam days, behind Maryville at 9.3 days.
- St. Peters, MO 5 mi, 4.2 days
- Bridgeton, MO 6 mi, 3.7 days
- Maryland Heights, MO 6 mi, 4.2 days
- Hazelwood, MO 6 mi, 3.7 days
- St. Ann, MO 8 mi, 3.7 days
Where these numbers come from
NOAA 1991–2020 climate normals from St Charles Elm Pt, 1.3 miles from St. Charles. 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.