Animated visualizations: Don't change the scale!!

I have an unhealthy obsession with weather - partly because we heat with wood, and partly because if it snows enough I get to use the snowblower on the front of my lawn tractor. Consequently I often have the weather radar  up on my browser.

By default, wunderground.com (and most others) show only the most current radar image - other than a total storm size I can pretty much look out of my window to get the same information.

By animating the map, I can see direction of movement - key if you are at the edge of the storm, and very important if it's a coastal storm which tends to sit and rotate rather than moving off. Equally I get to see the speed of the storm's movement, another important variable, and how the intensity of the storm is changing, denoted by the key on the right.

And here's the cardinal sin - if you're going to animate anything with a scale, don't change the scale halfway through the animation.

The initial scale has a number of shades of grey below zero (that really could be replaced with just one color, as this just means clouds with some snow blowing around).

5dBZ on the first scale (light snow) is a dark green. As the intensity of the storm passes a threshold a switch is made to the second scale. Now anything below 10dBZ is light grey, and interestingly, as is anything above 60dBZ. The second scale now also has some descriptions of the intensity. The new scale fails color blind users to a certain degree (mouseover to see) - the 45dBZ plus now looks very much like 15dBZ.

This isn't wunderground.com's fault - I would guess they pull the images from NOAA. I would also venture to guess the change in scale is as a result of the internal workings of the radar changing. Whatever the reason, software creates the scale, so it could be fixed.

One fix: as a change in scale is needed, create two images, one with the old scale, one with the new, for the period of time that that the animation covers. When you have enough frames switch over so that the animation only uses one scale. This isn't a great fix as that scale change will still confuse when viewing over longer time periods or intermittently through the day.

Much better would be to just have one scale (right) - as a member of the public (rather than a pilot for example), I don't think the values below 0dBZ, or above 65dBZ, mean much to me, so you could probably lump all of those into a bucket or two. I've still used a green to red scale, but identified the 'catch all' buckets at the top and bottom with colors outside the gradient. I've also extended the color range through purple. The greens have a lot more blue in them to help colorblind users (mouseover). A few other improvements - specify time between frames so that I can understand velocity (I always have to try to catch what the clock movements are), and state when the most recent picture was taken (not just the time of the current frame).