Chris Lewis writes:

Remember, (assuming proper ventilation) while the roof & eaves are
snow-covered they can't go above freezing until the snow cover comes
off.

It melts wherever there is enough heat, whatever the temperature. Snow can
melt in a below-freezing ambient from heat from solar radiation. That's
one way you get ice dams on a perfectly insulated structure.

It all has to do with that 32 deg F isotherm envelope I mentioned. You can
never guarantee it will enter and exit the house uniformly, and then you
will have a potential melt/refreeze situation.