The NWS forecast calls for extreme lake effect snow in the Chicago area, primarily in Cook county, on Sunday night into Monday morning, with 12-18 inches of snow or more possible. However lake effect snow is notoriously hard to predict.

I will resolve this market based on the sum of the official snowfall accumulations on Sunday November 9th and Monday November 10th at the Chicago O'Hare airport.

If it snows 8.1 inches, this would resolve yes, but 8.0 inches would resolve no.