The very short tail, and extensive yellow wash, point to possible hybridization with Western Kingbird. However, a search has turned up several photos of similar yellowish Scissor-tails, so who knows? The slight bill and very pale coloration seems to eliminate any possibilities other than Western, if the hybrid path is considered.

After more thought, a couple of other things strike me as being funny about the bird; the olive tinge to the upperparts and subtly darker gray of the crown and nape. Seems intermediate in most characters between Scissor-tail and Western.