I moved my comment to
http://flyertalk.com/forum/showthread.php?t=22870
and so far got great comments. Now I am moving forward to YXY*3nights.
AFAIK, AB sightings depends on four factors:
-weather
-full moon
-magnetic field
-solar wind activity
Yellowknife boasts 97% chance of AB sighting if you stay at least three nights there, and I guess the other are around the same, too.