Empyrial Storm

• WWizards of the Coast2018-07-13
  Official Ruling
  Each Storm’s triggered ability counts only how many times you’ve cast your commander from the command zone before that triggered ability resolves. If you cast your commander again later, you won’t get another copy.
• WWizards of the Coast2018-07-13
  Official Ruling
  Each Storm’s triggered ability can copy the Storm spell even if that spell is countered before that ability resolves.
• WWizards of the Coast2018-07-13
  Official Ruling
  The copies are created on the stack, so they’re not “cast.” Abilities that trigger when a player casts a spell (such as the Storm’s ability itself) won’t trigger.
• WWizards of the Coast2018-07-13
  Official Ruling
  If your commander was countered, that time you cast it still counts.
• WWizards of the Coast2018-10-05
  Official Ruling
  If you have multiple commanders, you’ll copy this spell for each time you’ve cast either of them. For example, if you’ve cast one commander once and one twice, you’ll copy this spell three times.

Rulings via Scryfall