A winter weather advisory is in effect for the Aurora area until 9am on Sunday. A complex winter storm will bring a mixture of freezing rain, sleet, and snow to the area. Colder, more seasonal air will follow this event.
A strong cold front pushed through Aurora this morning. Temperatures started off at around 50 degrees this morning and fell to around freezing by evening. This front has stalled to the southeast of the area. A low pressure has developed and is riding up the front. A southerly jet stream will pull warm, moist air over the sub freezing air at the surface. Snowflakes will form and fall into this warm layer, causing them to partially melt into ice pellets or water droplets. As these fall into freezing air at the surface, freezing rain and sleet will be the result. These icy conditions will develop after 8pm and make travel pretty dangerous. This is a very tricky setup that is hard to pin down until the event is underway. However it turns out, the National Weather Service advises people to exercise extreme caution when outdoors tonight.
Freezing rain and sleet will transition to sleet and snow from northwest to southeast after midnight. This will occur as colder air pours in at all levels of the atmosphere. Areas along and northwest of a line from DeKalb to Waukegan may see 2-3 inches of snow. The Chicago and Aurora metro areas may see anywhere from 1-2 inches of snow and sleet. Southeastern portions of the area may see a longer period of freezing rain, leading to ice accumulations of 0.1 to 0.25 inches. These areas will likely see less than one inch of snow. Areas may see greater snow or ice accumulations if stronger bands can form within the greater precipitation area.
Sunday and Monday will see arctic air pour in behind this storm system. Highs in the middle 20's with lows in the single digits are a good bet.