Board Thread:Speculation House/@comment-14640999-20140905083745/@comment-24994749-20141103143020

Assuming the Portals are Raven's semblance, maybe Qrow has the same semblance.

He or Taiyang could have arrived home and seen Yang and Ruby were missing and found something that pointed to where Yang had gone, so Qrow used a portal and that's how he arrived timely to save the day.