Could be Cargo, could be projected headwinds, or rough weather, or far more checked baggage than expected.
Look at the media baggage allowance, and with today being inauguration day it wouldn't be shocking to see some media people leaving California's capital possibly on the way to DC.
1ST AND 2ND BAG
ADDITIONAL BAGS
Domestic
Same as regular baggage allowance if no more than 50 lbs. (23 kg)/62 inches.
If overweight / oversize, flat media rate of 50 USD/CAD* applies.
3rd-25th bags 50 USD/CAD* each if no more than 100 lbs. (45 kg) and 115 total linear inches*
http://www.delta.com/content/www/en_...ial-items.html