Here is a zoomed in view of the radar along the S shore of Lake Michigan tonight.

Likely some multi inch per hour snowfall rates and potential whiteout conditions as this band moves over Chicago metro & adjacent areas.

Good thing this is occurring overnight & not during a major travel period.

To put it simply, if anything in a model moves more than one grid spacing in one timestep, small scale noise grows exponentially in time and dominates the model solution. This is obviously more likely in regimes of very strong winds.

A close examination of the 700 mb vertical velocity field reveals that the smallest resolvable waves, with a wavelength of twice the grid spacing, are responsible for this instability, as expected