Alan Contreras, an experienced birder from Oregon who is working in Boulder for the next 8 months or so, found a warbler today that he originally thought was a Pine, but he now thinks is a probable Bay-breasted, due to better looks. It's been in the same pine tree since noon, above the handicapped parking spot at 3005 Center Green Drive in Boulder. This is just off Valmont west of Foothills Parkway. There are only 2 pine trees in the parking lot and the warbler is in the one closer to the road.
All of this was relayed to me by Alan over the phone -- I haven't seen the area in question. Best of luck to anyone pursuing this bird.
Nathan Pieplow
Boulder, Colorado