Wind estimation is an art. Practice, practice, practice!
The easiest method is to use a wind meter but that gives you the wind at your location, not at the target's. So unless the wind is constant, be careful.
The wind meter is a great training tool. Record the exact value and look at the grass, the snow and the trees around you. Get a feel for the effect of the wind you recorded. When you detect the same effects at a distance, using your spotting scope or binoculars, you will know the exact wind value at that location.
Or get a buddy with his own meter. Vary the distance between you two and estimate the wind at the other person's location. Use radios to verify your estimate against the readings he takes with his meter.
The heat form the sun is reflected by the ground, producing layers of different air density. These layers will be pushed by the wind.
To read mirage, focus first on the target (here the ski slopes) and then rotate your focus button back 1/4 turn to focus on the mirage just in front of the target. Obviously the rest of your field of view will be out of focus but that is ok. Here the wind pushes the mirage to the right. At this angle, I would estimate the wind at around 8 MPH.
You can use the angle of the mirage to estimate the wind speed.
Many clues can be used to deduce wind speed and direction. Trees, brushes, leaves, snow, smoke... Use your meter and practice. Anything affected by wind can help.