Ice dams typically form when runoff from snowmelt reaches a(n) _____

Ice dams form when snow begins to melt on a warm roof and the runoff travels down to a colder area, particularly overhangs or eaves where temperatures are lower. As this warm water reaches the cold overhang, it can freeze, leading to the accumulation of ice. This process creates a barrier, or dam, that can prevent further meltwater from draining off the roof, causing it to back up under shingles and lead to potential water damage inside the home.

The formation of ice dams illustrates the importance of temperature differentials in roofing systems. A cold overhang is essential to this phenomenon because it allows the warmer meltwater from the roof's surface to freeze upon contact, which contributes to the buildup of ice. Hence, the correct answer highlights the role of temperature in the ice dam formation process.