I'm not sure about the complete picture on winter operations. The freight from Anchorage to Fairbanks runs 5 days a week, but that may be fewer days during the winter. Coal trains are still reported to be running from the mine at Healy, but of course this would be irregular and not nearly as frequent as before since the USG switched to natural gas for most of their military facilities. On the passenger side, the winter Aurora runs north on Saturday, back south on Sunday. This can be a really interesting operation during the winter, as this train frequently operates as a mixed train. This is the only mixed train remaining in North America when they add freight to the passenger consist, which I've heard is fairly frequent. This is your best(maybe only) bet to find something interesting in Fairbanks during the winter.