Gary Drescher wrote:

The current AIM (7-1-23) explicitly states that "forecast icing conditions"
are *not* "known icing conditions":

Nearly every place where there is a reference to prohibition of flight
into icing conditions, "known" is followed by "or forecast."

It's a moot issue. While, people talk about "known" ice certification,
the truth is that enforcement is literal and forecast ice will get you
in trouble with the regs.