What is this leaking?

I noticed for the first time Sunday morning and also this morning that there were a couple of spots underneath my car towards the front left side (drivers side) almost directly under the bumper between the headlights. There were about two table spoons worth of liquid both times.
Does anyone know what this might be coming from?

I have a 92STS 4.9. It was dark this morning and I think the stuff was black. I have 20% oil life left. Does this usually happen when it starts to get cold outside? This is the first winter I'll have with the Cadillac.
What things should I do to prepare for the winter?