The snow mounds like that when it is very warm and slushy. Instead of squishing and compacting under the animals foot it "flows" out and up. If you can discern claw marks then it is certainly not a cat. Cat's have retractable claws and don't use them when walking. Fox on the other hand can not retract their claws and generally leave claw marks behind. A fox track will also be more diamond shape when fresh, and cat tracks are more rounded.

