As millions of Americans hunker down for a massive winter storm sweeping the country, new maps are offering updated forecasts of snow and ice accumulations.

Heavy lake effect snow will develop Friday and Saturday, leading to quickly changing road conditions and dangerous travel at times.

A snow squall is expected to hit Chicago Friday during the morning commute, dropping 1 to 3 inches and creating dangerous whiteout conditions when roads are at their busiest.

Low temperatures likely dip to around zero or below tonight, and the wind chill may fall as low as -15 by tomorrow morning.