Beautiful depction! As I consider myself a perpetual student, I went you your blog to read what you had to say. Your discussion is good, but I must take issue with your explanation of why we see these boundaries in the water vapor imagery.
Water vapor imagery comes from channel 3 in the GOES I-M scanning radiometer and that channel is centered somewhere between 6 and 7 microns in wavelength. These wavelengths are where water vapor is most absorptive and so where it can obscure radiation from earth's surface. So, white areas are where less radiation reaches the radiometer and dark areas are where more radiation reaches the radiometer. Thus, white areas are where there is more water vapor mass in the vertical column and dark areas are where there is less.
Water vapor imagery results from imhomogeneities within the vertical distribution of water vapor in the mid-troposphere. These inhomogeneities come about through horizontal advection, vertical motions, and horizontal deformation. In your explanation, you say that what we see is due to a density gradient, but I don't see how that can be. Since the areas associated with the front are darker, more radiation is making it through the vertical column, which means there is less vertically integrated water vapor mass. I think what we see depicts something about mesoscale circulations set up by the boundaries you note. I'll guess that we're seeing subsidence and possibly frontolytic deformation (post passage) associated with these propagating boundaries.
As to why the secondary boundary dissipates, your hypothesis is as good as any I've heard.
Kim Elmore
