I know. It sucks. I have a big bud strain that is supposed to be indica dominant, but the way it has grown this season it has certainly shown its sativa genetics. Now it appears as if the buds are taking on the same sativa properties.
I doubt it will be finished before first frost where I live (deep south), so I am going to haul some black plastic out to the site and make sure the soil is covered well with the plastic and some insulating ground cover. When I can see it is going to frost overnight, I will take a can of sterno to the site, and cover the plant with a tarp. It is going to be a royal pain in the ass, but if you have put all this work into it, might as well let it finish.
Now, if your temps are getting so cold that your ground is in danger of freezing up on you, then it might be time to go ahead and harvest. Being further south than you are I should be able to ride it out all the way until sometime in November doing what I have planned.