Hi James, 

Yes, your observations are spot on!  There are some transitions and gradients in some of the maps that are not physically realistic.  The reason is that these maps are based on data that are averaged within the U.S. Climate Divisions: https://www.ncdc.noaa.gov/monitoring-references/maps/us-climate-divisio…. As you can see, there are large variations in the sizes of these climate divisions.  In regions where you have two neighboring climate divisions covering a large area, it's possible for the average precipitation to be quite distinct between the two divisions.  This would lead to unnaturally sharp contrasts in the maps you mention.  If the maps instead were based on data averaged in small, regularly spaced grids, then we would expect the contrasts to be more smoothly varying.