The teacher explained it in this panel:
Being able to call lightning requires the power to manipulate clouds to make lightning, which happens to also let you manipulate the weather somewhat. She’s been slowly drawing in the clouds and the typhoon so it arrived earlier than expected and thus goes away before the festival.
Seasonal death counter: 3 (+0, Subaru is on a roll!)
Poor Garfield just can’t stop losing! Subaru had some pretty gruesome deaths but Garfield is the one who is constantly getting the despair this season. It wasn’t enough that all the archbishops decided to show up, one of them happens to be a fucking dragon! One with ultra-speed regeneration, no less. Even the basic faceless cultists are no joke!