Alaska’s cargo operation has used 737-400 freighters for a while.  They are now the launch customer for a cargo conversion of the 737-700.  I read about them taking delivery of the first aircraft but wasn’t too focused on seeing one.  I almost ignored this departure since SeaTac has a steady stream of Alaska 737s.  I did decide to shoot it though when something about it looked different.  Sure enough, it was the cargo conversion.  A lack of windows and the cargo markings set it apart.