The 30 year average is very subjective, there is no climate cycle that corresponds to it, there is no scientific reason for having a 30 year average it's really just a matter of convenience rather than anything scientific.
For my purposes, I would much rather use an average that begins in 1950 which is when most of our airports came into operation, or 1960 at the latest. That way all stations are on an even footing since they were all in operation by 1960 at the latest. No 30 year averages or 10 year averages or what have you, just use all the data we have available starting in 1950 or 1960.
it's time to dump the 30 year averages.