Hi Don,
We have a sock at each end of the 2120m runway here at Cooma and it's not unusual, in fact more usual, to see them indicating differently.
The wind will always be affected by terrain and man made obstacles. The degree and resultant effects will change with the dominant air flow (wind direction).
As air is fluid, we can liken it to water flowing in a stream. Place an object (rock, stick, whatever) into a part that appears to be flowing smoothly in the down stream direction and you will see the direction of flow alter, at least in the vicinity of the object. Make the object bigger and the effect will be greater and more widespread. Place a number of objects in random spots and the flow is all over the place while still generally heading downstream. Added to this is the eddy effect around some objects causing the flow to momentarily head upstream as it swirls around like a mild whirlpool.
Also worth considering is the drag effect that the ground surface has on air flow. Say the lower level atmospheric wind is flowing north to south (northerly). Close to the ground the drag effect of the surface, even a substantially flat and smoothe surface, will cause a directional variation of the wind, say NNE or NNW, and sometimes more acute directional changes.
Hope this helps,
Paul