Lake-Effect Snow and West Michigan Roofs: What It Does and What to Watch

Because Lake Michigan runs north to south, the NWS Grand Rapids office says lake-effect snow reaches the West Michigan shore when the wind has a westerly component, while easterly winds keep it offshore. Within that, the exact wind direction decides which counties get buried. The office's own breakdown, by direction, looks like this.

Lake-effect snow almost always comes with wind, and wind moves snow that has already fallen. FEMA's Snow Load Safety Guide (P-957) explains that drifting snow is wind carrying snow from one part of a roof to another. Drifts form on a lower roof in the wind shadow of a taller part of the building and pile up against obstructions such as higher roof framing, dormers and chimneys. The depth there is greater than elsewhere on the roof, so the load is greater too.

FEMA calls the sheltered side of a ridge an aerodynamic shade: on gable roofs, snow blown over the ridge drops out on the leeward slope. With West Michigan's lake-effect winds coming mostly from the west and northwest, that often means the east and southeast slopes collect the deepest snow, even though they face the sun. FEMA also notes that valleys, where two roof slopes meet, accumulate greater depth than the open slopes around them.

The guide is clear about why this matters: an unbalanced snow load, deeper in some places than others, poses a greater risk to the roof structure than a uniform load. Snow from a steeper upper roof can also slide onto a porch or sunroom roof below, adding both weight and an impact force on framing that may not have been designed for it.

Structural failure from snow is rare on houses built to code. FEMA's guide opens by saying most buildings are not at risk of snow-induced failure. The damage West Michigan homeowners usually see is water. A deep, insulating blanket of snow over a warm attic melts from below, the meltwater runs to the cold eave and refreezes, and an ice dam backs water under the shingles. Long lake-effect stretches build that cycle up for weeks.

Wind is the other half. Fine, dry snow driven by a west or northwest wind can blow through ridge vents, box vents and gable louvers and pile up in the attic, then melt on the first warm day and stain the ceiling. Shingles that were installed late in the fall may not have sealed down yet, and wind can lift and crack them.

Michigan's building code anticipates much of this. The state's amendment to the residential code's climatic design table fills in the ice barrier column with "Yes" statewide, and the code's footnote ties that requirement to places where the average January temperature is 25°F or less or where ice damming has caused local damage. Many older roofs were installed before that rule, or with too little membrane at the eave, which is why the same houses leak in every lake-effect winter.

In Grand Rapids, October normally brings almost no snow and November averages about 7 inches, according to the 1991 to 2020 normals, so the fall is the window to fix what the last winter exposed. The useful jobs are the ones that address where lake-effect snow does its damage: eaves, valleys, vents and the transitions between roofs.

Clear gutters and downspouts so meltwater has somewhere to go. Have cracked pipe boots, loose step flashing and damaged vent hoods replaced before they sit under drifts. Ask whether the ice barrier at the eaves and in the valleys is adequate on the slopes that dam every year. And look at the attic, because air sealing and ventilation decide how much snow melts from below in the first place. After the season, a spring check catches what the snow and ice left behind.