Usually we'll have an inclining of trouble about a week out. That's when systems start to develop out West and South. But it usually isn't until 2-3 days out that we have a good sense of how much snow we'll get. The day before we'll usually have a good idea of the "bands" (i.e. which cities/towns will get the most snow). About 50% of the time all of these predictions are wrong, so YMMV.