High today is supposed to be +11F. Currently -2F. Supposed to warm up to a balmy +37F tomorrow before dropping to a low of 2F.
Back to greasing, I keep my grease gun in the garage on the house, which is heated (normally keep it at about 50F). If I have to grease in winter (usually a couple of times) I pull my tractor in the heated garage and let it sit for half a day before I try and get any grease in the zerks. It really depends on how much snow we get, and how often I have to use the tractor. Last winter we got diddly-squat for snow.
I use a low temp lithium-synthetic grease for zerks and pins.