I don't know how much damage you would do, but in general I don't cut things back until after frost once we are this late in the year since it would make them resprout and the new growth would just get killed by upcoming frost and so wasting the plants' energy. I don't wait until spring, but cut them down once we have had a hard freeze, after which I don't need to worry about reprouting. The exception would be if the vines themselves are actually dead, in which case you can cut them back to where they are live.

When do your clematis bloom? That will help answer when to cut them back in future years. Also, keeping even moisture helps, so I mulch my plants and water deeply if we haven't had sufficient rain to help prevent browning.

I agree with nhbabs about waiting until the vines have died back after a hard freeze before cutting back. I have found that clematis survive light frosts quite well so it may be late in the fall before they die back. For me that is usually late October to November.

Some clematis varieties seem to brown out more readily than others even with keeping the soil moist. This has been an exceptionally bad year for brown out on my clems. We've had many days in the 90s this summer with very low humidity. Keeping the soil moist didn't keep the vines from getting crunchy at the bottoms.

Even without cutting back earlier you may still get a few blooms on your plants this fall. Mine are just starting their rebloom. The blooms may be few and smaller than spring bloom but still nice to see.

That said, last year I had to cut one back to the ground around this time due to damage and it grew new foliage. It didn't seem to affect the plant this spring which bloomed profusely.

I would not do it now in your zone.

Pruning stimulates new growth which would not be as hardy when winter hits.

Thanks for the answers...OK so I better wait on that, they just look so ratty right now :)

But it is OK to cut them down after the winter sets in right? I was always afraid to cut them until it was getting time to start growing again.

Once they are good and killed back by frost it should be fine.

That doesn't happen here so I don't cut mine back until February or so when I do my roses as they will start growing again.

All brown. Do you really mean that they are ALL brown or is just part of the plant...some leaves, brown, the rest still having healthy looking leaves.

Cut back. I suggest before you do anything...do nothing.
Read about clematis at "clematis.com".

Learn about the 3 distinct genus of the plant and why, if any, pruning is done at their particular time.

About pruning. You cant kill a clematis by pruning at the wrong time....only set it back possibly in flowering time.

As far as winter is concerned, it depends too on where you have the plant--in sunlight, or in shade, next to a building, or out on a trellis.
Buildings provide protection, warmth, and plants can be mulched to provide further protection during and leading up to frost.
The age of the plants can matter. Young plants should be given protection in any case; older plants not so much.

As for their type; try to learn when they flowered; how they flowered and if they re-flowered a second time.
That can be a clue as to whether and how you should cut them back.

All the information you require is found at "clematis.com"

The majority of my clematis are summer bloomers, and I cut mine down any time after we have a hard freeze, such as below 25 degrees. I leave one or two sets of buds per stem. Because of how far north I am, on my early spring blooming plants I usually wait until I see sprouting in the spring since they often, but not always, are killed to the the ground and then I trim back any stems that are dead (which often is all of them.) However, IME you can prune any kind to a few buds, but if they are early spring bloomers, their blooming will be delayed.

So the simple answer is yes, prune them any time after the danger of resprouting is past in the fall up until they start swelling buds in the spring and the plant won't know the difference.