Chicago is bracing for a significant cold snap as lake-effect snow is expected to bring several inches of accumulation to the region. The National Weather Service has issued advisories, urging residents to prepare for rapidly changing weather conditions and potential travel disruptions due to snow-covered roads. The lake-effect phenomenon occurs when cold, dry air passes over the relatively warmer waters of Lake Michigan, picking up moisture and heat. As this air mass moves onshore, it cools and releases the moisture in the form of snow, often leading to heavy, concentrated bands of snowfall in areas downwind of the lake.