And then... GREAT GOOGLY MOOGLY!
It was this. And this. And this. Sort of.
Well maybe not, but we did have major meltage. One minute I was trying to chip the ice out of the shut off valve, and the next I had about a hundred gallons per minute gushing into my lap! Yay! We then had a bit of a flow control problem and sort of flooded the neighbor's patio, but with a little creative sweeping, and some of that ice melty salt stuff everything worked out just fine.
So despite the fact that the temperature was never above 40 degrees F today, the cisterns are once again lean-mean-water-accepting machines. There could be some great hulking chunks of ice still lurking around in there, but the emergency has passed. Thanks for all of your support and concern! Yay for the melting!