So I've bounced around to a lot of tutorials and different shadow making lessons and haven't really found one I'm looking for. The closest I came was one that explained placing a white solid on the ground and places where you want the shadow to appear, then using creating a light to cast the shadow.
Not sure if I should be applying that to what I'm going for but I'm trying to get the shadow to slowly cover the ground and my actor, then block out the sun ( i'll insert a lens flare here) as they overtake him.
Here's a tutorial on a sandstorm by Seth Worley which kind of has the effect but he doesn't go into creating the beginning shadow shots he has. The part I'm referring to starts at 38 seconds.