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1.
A bright, clear, sunny day after a night of snowfall.
Nothing is prettier than a January bluebird day in Seattle.
by Emersonia December 12, 2011
 
2.
An expression often used by out-of-date ski bums and boarders describing an otherwise beautiful, blue and sunny day. The expression is entirely unrelated to spring or to bluebirds.
Look at the sun! It's a blue-bird day!
by Pretentious Ski Fiend February 28, 2011