Big mountains or convoluted topography create unique currents of many kinds.  Temperature differences can be extreme with high vertical relief, and radical steepness will amplify their influence.  Dark, warm cliffs facing a low sun might stand adjacent to shaded ice, spawning sharp, powerful convection.  Localized eddies converge and overlap downstream of every terrain feature like rapids in a river.  Meanwhile, rotors and/or wavelets big and small could overlie all this confusion, or also be embedded within it.  When several of these forces combine the lift can be breathtaking, but close to terrain the sink they produce is especially hazardous.  Such currents combining and colliding can create ferocious turbulence, and more complex topography means ever less certainty.  An amazing sweet spot could vanish in a moment.