Is Storm considered as omega-level mutant?

On X-men wiki it says that she is omega-level mutant: link

Yes, She Omega Level on earth.

Isn't there's 12 omega Mutant that Apocalipse gathering ?

They are :
Jean Grey
Xavier
Living Monolith
Storm
Iceman
Sunfire
Mikhail
Bishop
Jean
Cyclops
Cable
Magneto
Polaris

not mention Nate Grey and Apocalipse too

No she is not. there are very few omega level heroes, the only ones are Hulk, Vulcan, Trauma, Silver Surfer, Thor, and then omega level objects-Mjonir and the cosmic cube

No. Storm is not an omega level mutant.
Those twelve aren't all omega level mutants.
I don't know what an omega level HERO is, but to be considered an omega level MUTANT you have to be able to transcend your bodily form and manipulate energy on enormous levels.
Storm is an Alpha Level mutant, so are Magneto and Apocalypse.

Some Omega level mutants are: Jean, Nate Gray, Iceman, Franklin Richards, Scarlet Witch, Elixr I believe, Vulcan and a few others.

It depends, I think, on whether Storm can use her powers in the vacuum of space. I was under the impression that her powers are limited to an environment with an atmosphere. So I personally wouldn't class her as Omega Level.

I think an Omega Level mutant should be able to use their power on a massive scale, affecting at the very least, an entire planet & its population. At most, their entire universe or dimension should be affected por their power.

Their power should also be able to be used in an atmosphere, space, & other dimensions or universes.

If anyone has a definitive list & criteria, please share.

JD