The storm motion (mph) is computed for every grid point from the mean wind 
through an average depth of the storm (from 850 mb to 300 mb).  It does not 
imply a storm will form, but if one is present it would move along the direction
of the shaft of the wind barb at the indicated speed. Each barb is 10 mph and 
each one-half barb is 5 mph. (NOTE: Not every grid point is plotted in order to 
reduce the clutter).