As I mentioned last week prior to the BUF/ARZ game, west coast teams in the Pacific time zone (ARZ is for the first half of the season, then they revert to Mountain time) who have:
1) Covered the spread in the prior week (ARZ won their week #2 matchup 40-7)
and
2) Are traveling across all 4 time zones from West to East
Have a 29% chance of covering the spread since 2005. It starts off at 38% against the spread traveling one time zone over to Mountain time and gradually continues to decrease with each passing time zone. By the time the Pacific teams reach the East, it drops all the way to 29%.
Keep in mind that this system proves that the team traveling West to East has difficulty when they have covered the spread the week before, as SEA did with their victory over SF last weekend. Just something to keep in mind for the future. Much is discussed regarding the suggested difficulty for teams traveling west to east (in the NFL, specifically. The NBA has a reverse effect), there will still be situations where the traveling team wins and covers 3/10 times. Whether or not SEA is one of those 3/10 teams this weekend is anyone's guess, but as you say, "it wouldn't be shocking to see it happen."