Two scenarios for the altcoin season
1. BTC confidently breaks past ATH and surges to 2x within a few weeks - this is a mega breakout without much respite, and alts don't get much traction until BTC stops after this sudden breakout.
2. BTC overtakes ATH but rejects/consolidates at highs for a few weeks before starting to accelerate higher and then doubling in a few weeks. Alts start rising right after BTC ticks before ATH while BTC consolidates. In the first scenario, alts start to increase massively a few weeks after BTC breaks ahead of ATH.