Yes, it's the Great Lakes. Throughout that week we had a strong NW wind blowing out of Canada.
Basically the air/water of the Lakes is warmer than the air/land around it. (Water's specific heat is much higher.) As the weather systems move across the Lakes, they fill up with water (warmer air holds more water than colder air). As the systems touch land, where it's colder, the now water filled air cools and hits it's dew point. Water freezes, and snow happens.
Of course now it's 40(F) and raining, (as well as thunder and lightning, which is a bit strange).