In Brief: Jupiter's first attack while apparently her weakest looks a lot more powerful than her later attacks. It consists of a giant lightning blast that can cover as small or big an area as the situation requires.

It's interesting that she must summon the lightning from the heavens instead of actually producing it herself as she does in her later attacks.

Cultural: Funnily enough the attack name doesn't make much sense as the attack doesn't feature one bit of thunder at all but is made up of lightning. Lightning and thunder are often mixed up even with native English speakers so Naoko Takeuchi can hardly be blamed that much for the mix up. Jupiter Lightning Bolt? Supreme Lightning? Hmm...

The Move: In the anime, Sailor Jupiter crosses her arms and pulls them over here face. Occassionally this clip of her is expanded for her to make a speech about summoning the lightning or about how she will defeat her enemy.
Once she's finished talking an antenae extends from her tiara and summons lighting from the heavens to itself. Sailor Jupiter draws the lightning in (still focused around the antenae) and then releases it at her target.

In the live action show, Sailor Jupiter starts the attack by spinning around while saying the attack name. while doing so she throws one of her legs up that acts as a lightning rod which attracks all the lightning she'll need from the clouds which have gathered. When enough lightning has been gathered she stops spinning, spreads her arms out in front of her and releases the lightning.