I believe Mercenary Pilot is right, it was mountain wave which was to blame for your predicament, or in your case, the rotor which is an associated phenomenon. And these things go down to the ground! In a glider, you often end up putting on as much speed as you can and fly into or directly down wind. In a powered aircraft I'd do the same (and I have done so!), but with full power!
What you missed was "wind and mountains" however cities lots of large buildings do very similar things. I bet you won't miss these two again.
PM