My 96' Lumina 3.1 usually gets 28-30mpg average in the summer. (31-34hwy) My mileage has gone down to 24-25 during this cold winter. Is this what you fellow lumina drivers normally get in the winter?

It's not uncommon to have lower mileage in winter driving. Longer warm-up, colder intake air and coolant skewing the mixture richer until the engine is fully warmed, tire slippage, thicker oil in both the engine and transmission, and more rolling friction on snow covered pavement all work against mileage. All that snow and ice clinging to the vehicle add weight as well.