My neighbor brought me a huge bag of grass clippings yesterday, so composting season has officially started.
I left the last pile of last season in place to see what happens. This chart shows the internal temperature in brown. The blue line is ambient air temp on my south-facing porch, and the green line is a sensor that I moved from my fridge out near the bins during winter.

Internal temp was always above ambient, indicating active life in the pile, and it stayed above freezing, barely. This is good because the microbes didn't have to go into a dormant state. I'll wrap the bin in a tarp next time to help retain heat and moisture, while shielding it from cold winds.
I'll have to turn this pile into storage soon to make way for new piles. I'm looking forward to seeing what it looks like on the inside and under the microscope. It's been undisturbed for 5 months, so I hope to see a lot of fungi.