Heavy lake effect snow will develop Friday and Saturday, leading to quickly changing road conditions and dangerous travel at times. Lake effect snow is expected to develop late tonight into early Friday, likely moving into northeast Illinois in the Friday morning/midday timeframe. Chicago weather: Heavy lake-effect snow Friday, Saturday; winter weather advisories issuedWinter weather advisories:A Winter Weather Advisory has been issued for Lake (IL), northern Cook, and DuPage Counties from 9 AM until 3 PM Friday. A Winter Storm Watch has been issued from Friday afternoon through Saturday morning for central and southern Cook County. The Winter Storm Watch in central and southern Cook, Lake (IN), and Porter Counties will likely be upgraded to either a Winter Storm Warning or a Winter Weather Advisory as we get closer to the event.