There is no doubt that the leading edge of the 2005 arrival front ran early this year.  Most coastal observers from Oregon to Alaska reported arrivals much earlier than average (around 7-8 days), many claimed new records.  

On the other hand, the peak movement, which includes interior valley reports, was only slightly ahead of average (about 4 days).  All in all, the migration looked a lot like the early migration of 2003, though more concentrated around the median and fading earlier.  The 2003 migration was complicated by a west side cold snap in early March.  This year temperatures were at or slightly above normal in March though very wet in the last half.

Of course, none of this provides any explanation for why migration begins earlier some years and later others.  Presumably the answer to that question is lying somewhere on the winter grounds....