Lots of good little tips on how to recognize weak under layers just by doing things like punching your ski pole or giving a little jump on the snow with your feet. I particularly liked that little pointer of recognizing a weak layer by have your track drop on your snowmobile. There are obviously more scientific ways of gathering information but being aware of the signals giving off by mother nature just through your movement in a snowy environment can be important to an overall assessment.  This guy is great along with all the good people at the the Utah Avalanche Center.