Today (12/31/19) ES spike at the end was accompanied by huge volume. Other than volume, do any of you guys know what other parameters to look for an end of day spike?

The ES had another one today. I wish I had an answer to your question, but I don’t.

I've been watching this also. On strong up days you can almost count on a strong move between 3:30 -4:00 EST. Don't know if it's algo's/computers but it's fairly consistent. I'm not a fan of trading that late but it's been tempting.