Hola Michelle
Literally yes, nieva mucho is using the verb in the simple present (it snows), not in the continuous present (it is snowing) - however, we sometimes use the simple tense to convey actions that "are happening" at the moment of speaking. It feels more natural to translate in English with the continuous tense though. But yes, technically, nieva would be "it snows" and "está nevando" would be "it is snowing."
I hope it clarifies it.
Saludos