Ice dam risk in Winona, MN
How often ice dams form in Winona
30.7 dam days a winter
High risk. On an ordinary house in Winona, conditions for an ice dam come on about 30.7 days in a normal winter, mostly in January and February.
Winona averages 38 inches of snow a year and about 86 days with snow on the ground. Snow that lies that long is what turns a little attic heat into a ridge of ice at the eave. 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 Winona
| Attic | Dam days | Risk |
|---|---|---|
| Air-sealed and well insulated | 13.1 | Moderate |
| Typical, some insulation, not air-sealed | 30.7 | High |
| Older or poorly insulated, warm attic | 52.7 | Severe |
Sealing and insulating a typical attic takes out about 17.6 days a winter here. It drops the risk from high to moderate. An older house with a warm attic should expect closer to 52.7 days.
Preventing ice dams on a Winona 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.
- At the next reroof, ask for ice-and-water membrane under the shingles from the eave to at least 24 inches inside the wall line. It does not stop a dam; it stops the leak when one forms.
Which to spend on first: air sealing or heat cable.
Winona winter, month by month
| Month | Snow (in) | Days on ground | Dam days |
|---|---|---|---|
| January | 9.8 | 24.9 | 10.5 |
| February | 9.3 | 24.0 | 9.1 |
| March | 5.7 | 14.1 | 3.5 |
| April | 1.6 | 1.2 | 0.1 |
| May | 0.2 | 0.1 | 0.0 |
| October | 0.1 | 0.1 | 0.0 |
| November | 1.4 | 3.3 | 0.7 |
| December | 9.5 | 18.5 | 6.8 |
Winona next to nearby towns
Winona ranks 80 of 103 Minnesota cities here for ice-dam days, behind Hermantown at 52.9 days.
- Holmen, WI 21 mi, 26.8 days
- Onalaska, WI 26 mi, 26.8 days
- La Crosse, WI 27 mi, 32.8 days
- Rochester, MN 40 mi, 33.3 days
- Eau Claire, WI 54 mi, 33.4 days
Where these numbers come from
NOAA 1991–2020 climate normals from Winona Dam 5 A, 2.5 miles from Winona. 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.