?-While it is true that snowy owls can originate from different NWT/ or Alaskan sources, the driver for southward migration of primarily juveniles is generally agreed to be at least partly based on food-source related (lemming and other prey species breeding/ survival rates)? and additionally, related to owl breeding success rates, creating food competition. These conditions should not be all that dissimilar from one end of the NYT to the other, there may be slight variances. Ebird, among other sources has shown a historic correlation between both eastern and western migrations (strong numbers 2011/2012) with much more moderate numbers in years prior. There does appear to be some correlation in overall U.S., based on what data is currently available.Here is an interesting link to a migration pattern study undertaken by BSU, one of the outcomes was that owls from the same breeding area do not overwinter in the same area, which would also support a
split-migration pattern between the eastern and western US. Another outcome was the high-degree of variability an specific owl population movement in migration from year-to-year -as Bud stated, we still never really know when and where they might show up. That said the best available data does demonstrate some correlations in overall movement in to the U.S..


http://raptorresearchcenter.boisestate.edu/wp-content/uploads/2010/04/fullersnowvariation.pdf