Varnishing at low temperatures
I'm not sure what you're asking, exactly, but here are some suggestions based on my experience varnishing in a similar climate. The colder temps don't seem to have much effect on the quality of the finish.

Keep your work piece and your varnish indoors until you're ready to work. If the surface and the varnish are warm it doesn't matter a whole lot what the air temperature is except with respect to drying time.
Drying time will be slower. Water and solvents don't evaporate at the same rate in cooler air. My strategy is to work outside and move the piece indoors after an hour or so. You'll still have some odor in the house, but not nearly as much as if you'd do the work inside.
If you leave the work piece outside, plan for drying to take three to ten times longer.