Some powders have problems as the temperature drops. With minimum loads in .38 special, I find using magnum primers with the same load for winter helps. It increases the pressure and burn improves. You could be having such a problem.
Most times a magnum primer is enough to push a lead bullet all the way through a 2" barrel. I have not always lived in the south and still remember what a real winter is like. Being so far north this could be a solution.