I think I answered my own question with a little deeper searching. I can use the greenhouse, but it would be more like "cold frame" sowing rather than winter sowing.

But since several panels are missing from the greenhouse (heavy winds last fall - the panels are on the bottom of the greenhouse, rather than the roof), I could leave those off for now, winter sow the seeds underneath those open spots in the frame, and then replace the panels later this spring when I want to start hardening off other plants out there (the WS ones would have to be moved outside then, I guess).

Perhaps that would work? The sides of the greenhouse would at least protect the flats from wind (well, assuming they don't blow away too, but since they haven't yet...)...

I did this last year in my unheated hoophouse (single layer of plastic on plumbing pipe, 12' x 26' x 6' high). I seeded in pots and flats, covered them with rigid clear plastic I had on hand (re-used from a dropped kitchen ceiling), removed the plastic once things sprouted, and basically theft them to themselves except for the occasional watering. It worked very well. I'm in the PNW though, so my winters are less severe than yours.

I grew several thousand vegetable and herb seedlings this way, including common thyme from seed (use fresh seed, a bit slow but worked OK).

Since you have those panels out in the greenhouse I think this would work well for you. I too have an unheated greenhouse, permanent structure. However, when the sun is out it gets rather toasty in there. Then dipping rather cold at night. For example, we have had several days in the last few weeks where the high will maybe reach 0 degrees outside, but in my greenhouse the temp will rise to over 85 degrees when the sun is out. So I don't put my ws containers in there because I think the drastic swing in temps might cause them to sprout early or the seed to rot.
I would think with those panels out you won't have to worry about the swing in temps though.

Thanks to both of you for the info! I lurked around the greenhouse forum yesterday as well...normally I don't start seeds, but with all this landscaping we need so many plants it's just not financially feasible to buy plants (and my hubby likes annuals, which I don't like buying every year). This will only be the second year we're growing veggies, just kind of getting into all of this.

Anyways, I read over there that some people in our zone start veggies and bedding plants as early as March in unheated greenhouses...and I'd really like to try that. So I think I'll go ahead and do the thyme outside on our patio table in true "winter sowing" fashion, and then next month we'll put the greenhouse back together (it's a harbor freight gh...the panels need to be more secure) and measure the temps to eventually start veggies and flowers in. I'm going to start half the thyme inside too, just to hedge my bets, and those plants will need the greenhouse later to harden off in (or wait around in, if I start them too early...).

Now I think I'll poke around and see what else I might be able to winter sow on the patio...