Last time I saw a Dowitcher at the CF was when the Purple Gallinule was here, but those were Short-billed.
(According to eBird, some guy named Rob Fanning saw 50 Short-billed Dowitchers at the CF on May 22, 2002.
Also according to eBird, it is a new sighting for the CF -- the 256th species, but the number looks a bit squishy.
More about Long-billed Dowitchers here.
The compete eBird CF list here, theoretically.
(sorry for earlier typos -- typing as fast as I could.)
Will post again tomorrow if I see it in the early a.m.