This all comes from the History of Creation I wrote up a while back. As such, it's highly uncanonical, and I'm still working the bugs out.
Mother of Storm Mothers
Greater Elemental Dragon of Air
Expressive Soul of The Elemental Dragon of Air
Attendant to The Elemental Dragon of Water
In the beginning of the world, when the essence flows of Creation were new and men and women had yet to walk or speak, Tiandian was sent from her place by the side of her greater self to attend to the Dragon of Water.
And for a time, Sacherevell, who knows the shape of things to come, walked Creation, and visited with all the Souls of Gaia. Briefly, he deigned to speak to the proud Tiandian, who for the amusement of the Dragons and their most honored guest, wove a storm that was perfect melody, percussion of thunder and lightning with a chorus of rain and howling wind. This tempest was, however, a well-measured thing, restrained for fear of breaking its harmony, and in that it was lacking. So it was that the Primordial rose, and went to the artist to deliver a message.
"You may be replaced." Said Sacherevell, with the greatest tenderness a Primordial might muster, for he spoke to a thing so below himself that his condescension to speak with it was an honor. "In all things, you may be replaced. If you fall, or are deposed, that Dragon from whom you spring will have another to take your place."
The storm grew troubled for a moment, and then Tiandian became enraged at the thought of being dismissed so inconsequentially, the sheets of rain pouring harder and more incensed. Her storm-song lasted for another year, with thunderbolts more brilliant, faster and sharper, and Sacherevell nodded at the change his offhand comment had brought.
When the first storm mother came into being centuries later, she was like her mother: a thing of terrible glory, awe-inspiring to behold. In her bitterness--for Sacherevell's comment and its implications had never left her--she tore at her offspring, determined that nothing should ever be like her, able to replace her, and broke its essence until it was a wretched, withered thing, and bound to the twisted form she had battered it into. That first storm mother was mighty still, but lessened and no longer possessed of the brutal majesty of the original.
Ever since, whenever a new Storm mother has been formed, whether deliberately or springing forth from the Essence of Creation, Tiandian will find it if she must, and break it so that she and she alone is the queen of the terrible, wondrous squall.
Tiandian's hide is the stormy, shifting green-black of the furious sea, with fangs of crackling thunderbolts and a mane of black, black stormclouds running down her massive spine that occasionally flicker silver from within. She has three eyes, each of which are the blank white of churning sea-foam. Seventeen pairs of wings beat at the air as she flies, in leathery, shifting patterns of gray. Even when not directly incensed, her body is in constant undulating motion, and the flash of her six tails shatters islands and breaks merchant fleets without notice.
She has been known to take on a human shape, albeit only when venturing deeply into Creation--she has developed a liking for the chaos and destruction she causes by her mere existence in her proper Elemental Dragon form, but sense demands that she reign in this affinity. She most often wears it when hunting her daughters. Her skin is the same green-black, and some truly foolish think her for a moment a potent Water-aspected dragon-blood. However, her veins glow electrically with every beat of her heart, and her eyes are the same foamy white as her true shape. Clouds follow her, and no matter where she goes, it rains--it pains her to have anything less than a great downpour in her wake. She stands taller than any man, her body is athletic and long-limbed, and her face is lovely, if austere.
Tiandian resides in a castle of iron that constantly drifts across the outmost reaches of the western sea, large enough for any mortal lord above water, but larger than the Imperial City beneath the surface. A constant tempest rages about it, both in reflection of her power and to sustain her storm serpent consort, Alarthanda.