SLC, MSP, and DTW all have similar average annual snowfall amounts (in the 40 - 50 inch range). They are well equipped to handle it so I wouldn't necessarily avoid them in the winter. You might want to also consider the LAX hub -- I hear it doesn't snow very often there
CVG will likely be your best bet for upgrades if you can find any routes that work through it. SLC would probably be next, followed by DTW/MSP/ATL which are all generally difficult upgrades from the west coast. There's a recent thread on decent upgrade percentages on SFO-JFK, so you should probably also look at the JFK hub.
Many a wise FTer have said "I'd rather go through MSP in a blizzard than ATL in a drizzle."