I didn't get a chance to give my lawn the last mow of the season since there were no dry weekends. It looks like it might be dry until the end of January. Would it do any harm to the lawn to mow it now?
You can now any time the grass blades are not frozen.
I've seen/heard mowers at least twice this month.
As a bonus, you might delay the first bloom of dandelions and cress by mowing now.
Anyone trying to keep a lawn British style/golf course short in this region is not going to be able to put the mower away in fall and then not get it out again until spring every year. In fact, if you are not watering a lawn here the growing season for it starts in fall, with growth possible any time during the winter it might happen to be warm enough, and ends when the summer drought shuts it down.