Does storm count spells cast before a spell with storm was cast on the same turn?

When a spell with storm resolves, its storm triggered ability counts every spell that was cast before it during the same turn. The Storm trigger looks back at the entire turn's history, not just the period after the storm spell was cast.

According to CR 702.40a, Storm triggers when you cast the spell, and the copies are created equal to the number of spells cast before it this turn. The game tracks a running count of spells cast each turn, and Storm simply reads that total count at the moment it triggers.

It doesn't matter whether those earlier spells were cast before or after any other storm spells. Every spell cast earlier in the turn contributes to the count, including your opponent's spells cast on your turn (e.g., via flash or split second interactions), instants cast earlier, and any other spells.

Example: On your turn, you cast Lightning Bolt, then Opt, then Grapeshot. Grapeshot has Storm, so it sees 2 spells were cast before it this turn and creates 2 copies — even though both those spells were cast entirely before Grapeshot hit the stack.

Note that copies created by Storm are not themselves cast (CR 702.40a), so they do not add to the storm count for any subsequent storm spell cast that same turn.