Wet dead bees on the landing board after a cold rain — condensation, chilled foragers, or is something robbing them?

First year in Minnesota, two hives, and I need someone to talk me off a ledge. We've had three days of cold rain, highs around 8°C, and this morning there were maybe 40-50 dead bees on the landing board and in the grass in front of my stronger hive, all wet and dark. A few more were crawling slowly on the board. My other hive had maybe a dozen. I didn't see any fighting, no bees wrestling, and I didn't see any bits of wax on the board. I haven't opened the hive because it's cold and it's raining again. My three theories: condensation inside the hive is dripping on them and they're dying of cold, or foragers got caught out in the rain and chilled, or something is robbing them and the dead are the losers. Which one is it, and is there something I should do today? I keep reading that condensation is what kills colonies in winter and now I'm convinced it's started.