It rains whenever Thor gets angry. Avengers to the rescue!
It takes almost no time for the storms to get really annoying. Everyone wants to send Thor to anger management classes, but Phil points out that not only would that never work, but they don't have the resources to provide psychiatric assistance to gods or demigods yet. So Bruce tries to teach Thor to meditate, to no avail.
Eventually, they all make a trip back to Asgard to find out from his family and friends how to deal with these moods... and still come up with nothing.
Pepper shocks them all by suggesting they have a few Asgard-style parties, see if bringing some of Thor's traditions here will help with his moods. "Throw a few parties, roast some animals over spits, have a couple of orgies, I don't know."
They all turn and give her their best open-mouthed stares. "What?"
"It's just a thought."
"NO."
"I'll bring Dr. Foster up here," Tony says. "That should help, right?"
It takes a while, but Tony's suggestion actually works.