Karen,
A lot of us successfully maintain a higher - than normal for winter - level of fitness through weekend runs with the Stay-Fit group. We have someone to run with, as well as folks willing to go long or short depending on what the individual or group needs are or what the consensus for the day is. We try to make sure we help those who might need certain mileage to incorporate into their training for upcoming events. What that means in Vancouver is, (not too sure about the specific of the Portland group) we're pretty much ready to run any distance you need. The benefit is, we're somewhat automatically "topped off" and can ramp up relatively quickly to get up to half- or full-marathon distance in short order.
Obviously, if your going to go out into the weather, you want to make it worth your while too. I try to keep my mileage around 85% for the "Half" distance and about + or - 60% for the full distance, every other weekend. This keeps those long runs in my picture and allows for relatively sane increases if I see a marathon coming up, that just needs to be run. For strictly maintenance, I'll keep a couple of weekday runs in the schedule too. These are usually a run with the dog to make sure he's also getting exercised during the winter months. Gotta take care of our furry friends.

With that in mind, please take a look at my post about running safer in the dark. Click to it here:
Reflections On Reflectivity</a>
I know how hard it is to get out of bed on those mornings when you just know it's cold out there. I find solace in the fact that I've got some great friends suffering right alongside of me, and we always find something to laugh about. Maybe not immediately, but we'll find it.

We are also planning more Off-Site (other location) runs in the Vancouver, La Center, Lacamas, area this winter to keep things interesting.
I hope this helps to answer your questions and I hope to see you joining us when you can.
Doug