The author of this article argues that Bitcoin Scaling is one tried and true metric to watch out for in identifying the next Alt Season. His explanations do make a lot of sense.
I also remember reading long ago a blog article that after Bitcoin has had its bull run and at its perceived maximum price, the speculators would start dumping bitcoin and start buying Alt Coins and this is when the Alt Season starts. Typically it takes several weeks for the Bitcoin bull run to last before the Alt Season starts, as was seen, according to this article, in the last bull run.
