Will my roof get ice dams here?

Type your town to see how many days a normal winter gives an ice dam the chance to form on your roof, which months they come in, and whether sealing the attic, raking or heat cable is the fix worth paying for.

Your city

3,206 US cities. A normal winter from NOAA's 1991–2020 records, not a forecast for this one.

Your attic moves the answer more than your town does

An ice dam is snow melted by heat leaking out of the house, refreezing at the cold eave. Pick the attic and watch the count change.

Attic Air-sealed and well insulated Typical, some insulation, not air-sealed Older or poorly insulated, warm attic

Days per winter an ice dam can form
Duluth, MN	38.4	Severe
Minneapolis, MN	22.8	High
Portland, ME	22.4	High
Buffalo, NY	21.2	High
Chicago, IL	12.8	Moderate
Boston, MA	10.4	Moderate
New York, NY	3.2	Low

Buffalo gets 95 inches of snow a year to Duluth's 56, and still has fewer dam days. Lake snow comes in bursts and often melts off; Duluth's lies on the roof below freezing from December to March.

What your number means

Very unlikely under 1 day: Snow rarely lies on a roof below freezing long enough. Nothing to do.
Low 1 to 5 days: A dam in a hard winter, usually small. Clear gutters before the first snow.
Moderate 5 to 15 days: Most winters bring a few. Air-sealing the attic floor stops most of them.
High 15 to 35 days: Expect them every winter on an ordinary house. Seal and insulate the attic, and rake the first few feet of roof after big storms.
Severe 35+ days: Dams form for weeks at a time. Attic work first; an ice-and-water membrane under the shingles at the next reroof.

Every city, by state