Barn Swallow flock returns
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http://www.wunderground.com/radar/map.asp. Then click on the "X" in Oregon to go to the link to the radar facility that covers the northwest part of the state.
Weather permitting, it should be possible to watch this event live as it is repeated daily until early October.
A published paper providing more background information about this phenomenon can be found at:
http://www.engr.washington.edu/epp/psgb/2007psgb/2007proceedings/papers/P1_couse.pdf