  This paper studies the regularity of the free boundary for viscosity
solutions to a parabolic Bernoulli-type free boundary problem with variable
coefficients. The main result is that Lipschitz free boundaries are $C^1$ with
a normal vector that varies with a H\"older modulus of continuity in both space
and in time. As a consequence, the viscosity solution satisfies the free
boundary problem in a classical sense.
