Howdy,
Interesting find

I keep looking in/on the snow to find a
Boreus some day, but this is nice and peculiar too

I have no explanation really, especially not if these occurred in numbers. Maybe the warm november made them develop/hatch prematurely?
Habitus seems to suggest something
Dorytomus-ish I'd say, but then again, I don't do beetles so ...
Cheers, Arp