Very good explanation. As you saw my conveyor belt image was from comet and there is more material about it - I wonder if Dave could link it here.
There are two kinds changes we see: changes in time and changes with height. I understood Julie also asked why we see the change more clearly in velocity than in direction, and part of that explanation lies within averaging over cylinder (remember the CDs in the pre-reading material ?)
Another comment to Ka's first question about the reflectivity to amount of rainfall-conversion: yes we see more reflectivity in snowfall in warmer temperatures, but the larger snowflakes also contain more water. However, the reflectivity grows with 6th power of diameter, while the amount of water grows only with 3rd power of diameter. All dbZ-to-mm equations assume some particle size distribution, this is always a default, and in snowfall the assumption is worse than is liquid rain. Also on the liquid rain, some people use different dBZ-to-mm equation for convection (large drops) than for stratiform rain (small drops).
What is more, the density of snow varies: fluffiest snowflakes contain 90% air, whle the heavily rimed almost graupels are 40% ice, 60% air. Knowing the density of snow is a subject of intensive research, especially with polarimetric radars.
Thank you for active participation, good luck with continueation of the class
Elena