I think that the severity changed as the day went on. I know that it was not predicted to hit Birmingham Alabama and they got slammed. I am not so sure about Atlanta. I also believe that they called for a gradually building storm and it pretty much hit all at once.
Essentially, where the DC area weather predictions have been off predicting larger storms, these folks were off predicting something smaller.
The real problem is people unwilling to look out the wondow and go "This looks worse then I thought" and taking off then. I get wanting to save hours, I do that all the time and bitch when I am forced to take time off when I could have worked. At the same time, I know that I will leave early if things look like they are picking up speed. I know my husband will do the same thing. We both are used to living with snow and ice in the winter and are comfortable driving in it but know when it is best simply to get home.
The problem is the number of people who do not trust their gut and stick it out or rely on the weather people to tell them when to go. That mass release of people at the same time is simply devestating and insures that traffic is going to be FUBARed.
When it come sto weather, people really need to learn to trust their instincts.