I think you'll want to keep it covered to keep it from getting too wet, but it will probably continue composting. If you have a second bin, you could start that one and leave the first one and by spring it will almost surely be done whether you turn or not.

My compost bins are covered and have been covered for a number of years now because I found long ago that left open the rains and snow made the material too wet to compost and when the temperatures dropped to below freezing long enough that quite qet compost would freeze solid. With a cover, and now being able to limit the amount of moisture to just enough to keep the aerobic bacteria happy digestion continues all winter, except at the exposed edges which normally do not get digested anyway unless mixed into the pile better.
A wire bin will be more difficult to cover unless a frame to support the cover is constructed.

Thank you both. Since the compost I have doesn't reach the top of the wire bin, should the cover fit snugly right on top of the compost or should it rest on top of the bin, leaving air space between it and the compost?

All you want that cover to do is keep any rain or snow off the material inside, it does not need to be a tight fitting cover. Any cover does need to be wide and long enough to cover the material but it is not a totally enclosing lid.

Toad, it will be difficult to cover the bin against what freezing weather you do get....if the winter days stay below freezing for at least a week, parts of the pile will freeze---it has to, its got moisture in it. Otherwise, the parts in the interior will stay mostly in a range where temperatures will still invite additional stuff be put in. Not much action as far as breaking down will happen, its generally too cold for that, but as garbage goes, its better to put it in there rather than throwing it away.
As the days get milder, the action will resume--then stop as temps drop.
The cover over the top will prevent too much snow/rain/snowmelt causing the pile to attain too much moisture---thus stopping any action by that route as well.
Too much moisture too will cause the pile to emit unwanted odours.

GRass clippings, what you mow with the leaves you pick up, will help retain the temperature somewhat if you leave them ontop for a couple days...a week, then turn them over.
This will add much nitrogen and phosphurus....and to speed things up somewhat more, add a couple handfuls of granular lawn fertilizer to the mix.

An easy cover can be made with the use of those large cleanup bags by cutting them open and get double their size. Use a staple gun to affix the cover where you can.
With a wire bin, try putting a piece of wood against the interior wall, then staple through. A corner can be left open so you can add through the winter.

The OP is in Bellingham, wa., zone 8. I don't think winters are that cold, are they, Toad? When my son lived in Seattle, they did get a little snow and sub-freezing temps at night, but days were generally above freezing. That compost might not freeze, at least not completely. It could well keep breaking down slowly, even without huge additions.

Karen

You're right Karen, our winters don't usually get much snow, and the temps stay in the 30s and 40s with some 20s here and there. However last winter we were snowed in for 10 days and it got down to 10 degrees F.
I'm thinking of covering the bin, but continuing to add and turn as I can. In spring I'll sift to remove the larger, undigested pieces.
Thank you all again for the comments. Very helpful.

I'm in rainy Oregon, and I have the same question. It sounds like some black plastic on top would be sufficient. Do ya think?

Rain2Fall

If you use black plastic, cover it loosely. You want to reduce the amount of water, but you want to allow air to continue to circulate.

Whoops. I left my pile last night uncovered and it looks like it rained a lot through the night. The problem is that I have a compost pile on my property where we don't live yet--haven't built a house yet. That makes it difficult travelling back and forth.
Can I save the compost pile if I just turn it a bit or can I expect bad consequences?

If it got too wet, it might get smelly. If you turn it, you can reduce the smell. Adding dry "browns" (leaves, shredded paper, etc) can also help.

So I guess you're saying that once it starts to faul as evidenced by a bad smell that you can still turn the process around?
I just get worried a bit because sometimes its hard to get to my property on a daily basis to check it.

Even if it starts to smell bad and you can't get to it, it will eventually decompose into something usable.

Ok. just wondering because I read that once it starts to spoil is can become toxic the your garden plant roots.