Look to his earlier books for tighter, more academic drawing, watch him loosen and become confident with any visual challenge, and have the delight of seeing him toss off late sketches with an unconscious grace. The last sketches are almost conceptual art - more suggestion than closely written description.
I believe I'm the only member from Philadelphia - if anyone else is out there drawing, let me know and we can start our own chapter!
Explore Turner's sketchbooks
http://www.tate.org.uk/servlet/BrowseGroup?cgroupid=999999995
Get to know Urban Sketchers
http://www.urbansketchers.org/