Being a resident formally of Mo. for 40 years, yes a have witnessed several snakes and raptores doing what you described. One very in particular incidence was a very warm 2 day period in Jan of about 1976 where i was visiting a bud that lived in Holt Mo. Some place not to far on a back road we had pin pointed a timber den sight several years before and just for the heck of it went there to investigate if there would be any chance at all of the snakes taking advantage of the warm weather. They were ! While we saw no juveniles, there were around 7-8 adults basking on the rock ledges.
The next docu. time was the first year I moved here outside of Emporia, KS. 3 years ago we had some very warm weather here in Jan. and on a road where the water treatment center is located for my small township, we have a bleed over ( what i call a canal ) that runs opposit the road. There was a swoop of a redtail hawk in which we have dozens of in this season, that landed on a snake. Being a holder of the falconers permit many yeas ago I knew what the bird would be doing at capture of the snake where it would entrail the snake immeadiatley. The hawk took off right after that with the snake in it's talons before I could ID the snake. I would think it was either a garter or water snake.
Chambo