Historical Rules · 29 April 2022
Rule 702.57b
Official source text from the 29 April 2022 Rules release
A forecast ability may be activated only during the upkeep step of the card’s owner and only once each turn. The controller of the forecast ability reveals the card with that ability from their hand as the ability is activated. That player plays with that card revealed in their hand until it leaves the player’s hand or until a step or phase that isn’t an upkeep step begins, whichever comes first.