Hours and intensity of sunlight is an issue for Winter growing. Days are shorter because the sun is at a lower angle which also makes it less intense, hence the cold.
There's a youtube channel by a market gardener in KY that I watch. He says that even the cold/shade tolerant plants will stop growing in at some point in Winter but they'll stay alive for continued harvest as long as it doesn't get too cold. Row covers at night or on really cold days will help keep things alive.
They're best thought of as season extenders.
Personally, I doubt I'll want to walk out to the high tunnel when it's 20 degrees and windy outside possibly with snow on the ground. I'll go out and knock the snow off when/if needed but then it's back to the wood stove.
To heat a greenhouse, you either need a glass house or double layer of poly but even then, you'd probably pay more to heat it than the cost of the veggies.
Personally, I doubt I'll want to walk out to the high tunnel when it's 20 degrees and windy
Currently 40 - both temp and wind gusts. Just started the truck and it's heater and will give it plenty of time to warm up the cab. Gotta grab some groceries. My working outdoors vacation days have been getting whittled down one by one. Will get the dump run done, frame 7 up and some seedlings planted out but not much more.
I can pick up chain link top rails from Menard's after work someday. Don't need the trailer. I can hang them off the right side of the truck with straps to bed pockets, mirror and up under the hood. BTDT and the body on this truck is rough enough to not worry about a couple more scratches.