First, there is a risk of tornadoes Tuesday and Wednesday (see below). I'll update those threats tomorrow and Wednesday.
There is a risk of serious flooding developing in the southern Appalachians, along the Gulf Coast and in the Ozarks. Where I have placed the hatched lines, there is a chance of isolated amounts of 10" or more between now and Sunday evening.
Here is the outlook for 3 inches or more of snow. These maps were put together by putting many computer models together (an "ensemble").
It is impossible this far out to forecast where the heaviest snow is going to be. That said, some spots may have more than 15 inches or more! So, if you are going to be driving or flying through the indicated areas, you need to keep up on the forecasts this week.