For example, how Winston County- roughly 99 percent white- gave "only" 81 percent to McCain? Maybe, but I'd guess that whites in most black-majority areas voted well over 90 percent against Obama; and metro Birmingham probably had equally extreme polarization, especially in the outer suburbs.
Rural northern Alabama may include the whitest areas of the state, but I don't think we can extrapolate statewide numbers from those counties.
It's a noticable pattern, that in very white areas in Alabama, Mississippi, and Louisiana, Obama managed to get 15-20% of the white vote. Meanwhile, in areas that are majority black, or 50\50, Obama managed to get only 5-10% of the white vote, so the exit polls may not be wrong.
Perhaps. These are the top 5 AL counties in terms of raw number white population:
number of whites Obama % black% est. white Obama%
Jefferson County AL 352,991 52.2% 41.5% 12.4%
Mobile County AL 244,899 45.3% 34.7% 12.0%
Madison County AL 218,331 41.9% 24.0% 18.9%
Shelby County AL 156,441 22.8% 10.6% 12.6%
Baldwin County AL 148,448 23.8% 10.1% 14.1%
For MS:
white pop. 2008 Obama % black% est. white Obama%
Harrison County MS 119,673 36.6% 24.0% 13.6%
DeSoto County MS 111,226 30.5% 22.1% 9.3%
Rankin County MS 107,295 22.8% 20.5% 3.1%
Jackson County MS 91,924 32.7% 23.0% 10.6%
Hinds County MS 77,884 69.2% 67.0% 4.9%
The estimated white Obama vote presumes blacks being 96% Obama, as national exit polls say. In any case, it looks somewhat more positive for Ala. than Miss.