I know I asked basically the same thing earlier, but this is with respect to the 1991-2020 30 year averages, correct?
To that end, is there a specific reason for using the 30 year timeframe? I believe @dendrite mentioned they were updated every 5 years if I recall correctly. My guess is that the recent 30 year look back allows for near term trend identification and accounts for relevant, real-time-ish temps.