Does anyone here know Latin

[ptc24]

So I wanted some Latin for "out of thin air" - basically I wanted a more scathing version of ex nihilo or a priori. Google translate suggested ex tenues auras, and I like the implication of "tenuous", but I'm not sure it's a) even remotely correct and b) whether there's an actual Latin idiom that carries the same air of dismissal, and which doesn't make you look stupid for using it (and lead to people pointedly wondering where you got that phrase from).