I'm near the mouth of Parleys Canyon in Salt Lake and I see what your describing a couple times each winter. Finally get a warmer day and the ground around the hives is littered with dead bees. When the snow melts, there are piles of dead bees in front of the pallets. I was pretty nervous the first few times, but I popped the lids on serveral colonys and there are a lot of bees in there. They go out for cleansing flights and don't make it back. I think it's more pronounced with the Italians and the huge population they try to keep. This has been an extremely cold winter this year, and some of the colonys are still on 7 frames. Of course, they use a lot of stores when the colony is that large and they start to crank things up. I have added granulated sugar over the inner cover when they get too light, and they have taken it. Keep an eye on things, dandylions and flying weather are still 5 to 6 weeks away. Maybe longer this year, since we haven't had our usual January thaw.