Hey Tyler, I established some bottom temperatures for myself long ago. If the ground is dry I can go out at about 19 degrees at the lowest. I have done a few runs as low as 16 though. If the ground is wet (rain or snow) I generally put on fivefingers below 40. If I will be running through snow of any depth I can make it about a 1/4 mile straight without problems. The one time I ran a mile or more in snow of 4-6 inches deep it resulted in severe frost nip (maybe frost bite). It took about a day for my feet to recover.
I got to about 27 F as long as it was dry. If it's wet and below freezing, forgetaboutit! Welcome to the BRS!