Light snow and flurries will come to an end Tuesday night, but the cold temperatures will be sticking around. And that's all thanks to a deep trough of low pressure (dip in the jet stream) out east and a big ridge of high pressure out west.
With the jet stream winds coming in from the Northwest this week, several smaller scale low pressure systems will slide down through the Northern Plains and into the Midwest and Great Lakes. These typically don't have much moisture with them and most will bypass Northern Illinois and Southern Wisconsin to the west and southwest. However, one weak low may be just close enough on Friday to squeeze out a few flurries during the afternoon and bring a reinforcing shot of cold air Friday night and Saturday. Saturday will be a cold day with highs staying in the teens!
By the time we get into the latter part of the weekend, the big ridge out west flattens a bit over the middle of the country. This will allow a stronger low pressure system to move into the Great Lakes by Sunday night. A slow return in moisture from the South, combined with colder air from the North may bring light snow to the Stateline on Valentine's Day, possibly with some minor accumulation by Sunday night. So if you're heading out Sunday to celebrate with that special someone, you may be dealing with some snow. If you're planning on heading out Saturday night it should be dry, but just cold! A good night to snuggle under the blanket.