exoplanet - What is the most extreme weather found on another planet?

I would say on the gas giants: Jupiter, Saturn, Uranus and Neptune.

Storms on Jupiter, such as the Great Red Spot or Oval BA, are well known.

Storms on Saturn, such as the Dragon Storm or the Great White Spot, are well known.

Storms on Uranus are not common, but there is one: the Uranus Dark Spot.

Storms on Neptune are very common: the former Great Dark Spot, the former Scooter and much more.

Storms on the inner planets also happen:

Storms on Mars are pretty rare, but one type is not, a dust devil.

Storms on Venus are common, cyclones similar to Earth's storms appear.

Storms on Mercury are extremely rare, mostly due to the lack of an atmosphere.

Storms on Earth, you all know.