In their AFD, they stressed "NIGHTIME" snowfall as 2 to 4 inches (as that map generally shows.) So, I'm guessing they think the lakeshore will get smacked pretty hard before 7 pm, and then what you see on the map is the rest of the night. Sort of an odd way of doing things...
Heavy snow coming down here. Back to 1 to 2" per hour rates. If it snows like this for hours, I could easily see these 'new warning" amounts being met.