Lake-effect snow is local weather with a simple engine. Cold air blows across the warmer, open water of Lake Michigan, picks up heat and moisture, and drops snow where it comes back over land. The Illinois State Water Survey notes that north and northeast winds are the setup that boosts winter precipitation from Chicago eastward. Early winter is prime time, because the lake is still relatively warm and it rarely freezes over completely.
Chicago is on the edge of the snowbelt
The heaviest, most persistent bands usually set up over northwest Indiana and southwest Michigan, where the wind has a longer fetch across the lake. Chicago is at the southwest corner of that water, so the city is not the center of the snowbelt. It still gets the enhanced snow, especially along the south lakefront and the eastern suburbs, and a northeast wind can push bands well inland. A forecast that says “a coating to two inches, with locally higher amounts” is the sentence that hides a lake-effect band. One town gets a dusting. The next town over gets six inches of wet snow in an afternoon.
That snow is often dense. It clings to trees, packs into drifts against a house, and loads a roof valley. It is a different problem from the dry inch a clipper leaves behind.
What it does to the heating system
High-efficiency furnaces and boilers exhale through plastic pipe, usually on a side wall. Drifting snow and wind-driven flakes pack those intake and exhaust terminations. A blocked vent will shut a modern furnace down on a safety switch, which is the equipment protecting you, and it also leaves the house with no heat while the snow continues. After a lake-effect burst, look at those pipes. They should be clear, pointed the way the installer left them, and sitting above the typical drift line. If the same termination buries itself every winter, it needs a new location, not another midnight reset.
Power blips come with the heavier bands. A boiler or furnace that does not restart cleanly after a short outage will sit off while the house cools. Exterior-wall plumbing is the first thing to suffer. If you already know a circulator or an igniter is marginal, lake-effect season is a poor time to wait. The boiler tune-up and a furnace check are the boring appointments that keep a snowy Tuesday ordinary.
A practical habit
When the wind is northeast and the forecast mentions lake enhancement, clear the vent terminations before you go to bed, and keep the heat running at a steady set point. Zima HVAC works on these systems from our shop in Mundelein. If a furnace is locked out and the vent is buried, or if it will not restart after the snow, call (847) 323-8314.