Ice Dam Prevention: Local Deadlines by City

Deadlines for the largest cities

Find every covered city for your state in the list below.

How an ice dam forms

The mechanics at the eaves

Warm air leaks into the attic and heats the roof deck. Snow melts against the warm deck, runs down to the overhanging eave, which stays at outside temperature, and refreezes into a ridge of ice. The ridge traps later melt, which pools and can work its way under the shingles and into the ceiling below.

The three levers are air sealing, insulation, and ventilation — all of which keep the roof deck cold and uniform. Roof raking and melt socks treat symptoms; the attic work treats the cause.

Raking and heat cable

After a storm drops four inches or more, rake the lower three to six feet of roof from the ground with an extension rake. Keep clear of the edge and never climb an icy roof. For a roof that dams every year, heat cable installed in a zig-zag at the eaves keeps a drainage path open; run it only when needed.

How we time the season

We estimate the start of snow season from monthly snowfall normals — the first month that averages at least one inch of snow — and pair it with the live snow-and-thaw outlook on each city page. Because it is an estimate, we label it as such. See the methodology page for details.

Find your state

Frequently asked questions

Other winter-prep guides

See the methodology for how these dates are calculated and their limits, and the data sources behind them.