Hello again Zach.  I uncovered another piece of information with reference to Nodaway Valley, Snowy Owls, and even you Canadian owls spotted in Missouri - Northwest Missourian: Community.  So, it seems you're a zoology student at NWMSU (maybe under Dr. Easterla?).  I was too in the beginning when I started at NW in 1965, Dr. Easterla in his first year there and became my mentor of sorts and in essence introduced me to modern day birding which since evolved into a life in the field as a marine mammal and seabird biologist which is now winding down as I gradually phase into retirement.  An amazing introduction that first Fall of 1965, my first Red-breasted Nuthatches and Pine Siskins, neither of which I had ever heard of before.  That Fall/Winter of 1965-66 was also an epic NW Missouri winter finch year, Red and White-winged Crossbills and Common Redpolls, the fun never seemed to stop.  I even flunked out that first semester, thanks entirely to the newly discovered world of birds, derailing my otherwise 'tornado chasing' career aspiratons, and set out to explore and travel every single inch of road in all of Nodaway County, ...and did!  I had been bitten by the bug pretty bad.  Don't let that happen to you :-))  Having to sit out a semester, drive a taxi around Maryville, an interesting and eye-opening experience in and of itself :-)), and bird, bird, bird, I came back and the rest is history.
Anyway, back to the Missouri Snowy Owls and apparent die off due to suspected starvation, perhaps just a little mouse here and there scattered over largely vast monocultural farmland isn't really sufficient to sustain them for too long, unlike a huge explosive burst in lemming populations during an Arctic summer.  Out here in the Pacific Northwest and coastal areas of Washington and SW British Columbia, the large numbers of Snowy Owls are doing fine, but their prey are almost entirely found in the abundance of much larger fare, waterfowl, a variety of ducks, coots, larger shorebirds, gulls, and Western Grebes, judging from pellet analysis and piles of avian body parts strewn about.  Perhaps that's what sustained the congregation at Smithville Lake for as long as it has (or did), ...water birds?  During winters where local prey isn't critically low and the owls remain on or near their home turf but perhaps lemmings difficult to access, I have heard and read of accounts that Snowy Owls actually head out to sea, particularly the middle of the largely frozen over Bering Sea (Alaska) where most of the world's population of Spectacled Eiders mass tightly in the polynyas there and upon which Snowy Owls find easy pickings.  Similar reports come from far at sea and open ocean in the high North Atlantic where Snowy Owls subsist on seabirds and apparently sit around on icebergs (and the occasional transiting ship) when in need of something to sit on and rest.
I look forward to future reportings from Nodaway Valley CA (I plan to visit there myself next week sometime), and elsewhere from the most extreme NW corner of Missouri (Nodaway, Holt, Andrew, and Atchison).  Apart from Squaw Creek NWR, that far corner seems to be kind of a 'dead zone' for reports appearing on MOBIRDS given they are so few and far between.
Richard Rowlett, formerly Maryville, MO
currently: Seattle, WA 
The Audubon Society of Missouri's Wild Bird Discussion Forum
ASM Website: http://mobirds.org/
ABA Birding Code of Ethics