They close the dome when the weather is bad.
On the inside of the roof, you see painted blue sky and nice white clouds!

Inside Ocean Dome, in the world's largest indoor pool,
the weather is always perfect:
No rain, no heat waves nor cold spells.
The sky is always blue!
The waves are always perfect: Never small and boring. Never dangerously big!
The water is pure: No salt and pollution (but there must be a lot of chlorine)!