So long as your top entrance is not blocked, I wouldnt worry if the lower entrance was frozen closed. Yes, clean it off/out when you get the chance, but its not an emergency you need to be out there with a flashlight doing at 3 am.
Snow is drifted up around my hives on the hill, lower entrance cant be seen, but the upper entrance is open if they need ventilation. The hives at the sunflowe field were drifted in as well, and I have most of them wrapped with NO upper entrance, so... I had to go check on them and clear the entrances. Those were the ones that I gave up on and cut the openings so they also had an upper vent. Really wet in there, enough so that it made me afraid of losing those hives.
The winds have been out of the south and southeast, with a wind chill of 25 below and LOTS of blowing snow.. I would guess it got blown in, melted and attempted to run back out.
Some winters here are mild enough that we do not need to wrap. Winters like the 2013/2014 winter were as bad as Perry's winter. (OK, we didnt get as much snow) 50 blow plus for extended periods with over 4 months of temps NOT above 25 degrees (f) so its hard to tell if wrap is needed or not. This winter has been mild and damp. plenty of 40 degree days up to a couple weeks ago, then the temps dropped to -20.. today it warmed up to freezing,(32) next week it looks like it will be nearly 40 again...
How do you prepare for that?
The answer is, you prepare for the worst, and then hope for the best!