It is possible to find unexpected wave any time and anywhere, even over perfectly flat country and even on a day with light surface winds.  Such phenomena might exist in only a very limited band of altitude, maybe not offering a chance to climb yet still useful in gaining ground or saving time.  In the luckiest cases a high climb in wave can provide a more certain, and perhaps quicker path to where you’re going.  On the other hand, if ridge lift or thermals down below are strong and the wave above is not, you might waste a lot of time climbing unnecessarily by pursuing the high road.  Or maybe the actual wave is extremely weak but energizes a band of stronger-than-average thermal lift.   Also, the sink of an unexpected wave can ruin an otherwise well-planned glide if you fail to recognize it in time and react accordingly.

Whatever your strategy, anytime you encounter unexpectedly smooth lift or sink, or turbulence, or particularly linear cloud edges, and especially downwind of mountains, bear in mind the prospect of wave – and its consequent affects as well.