So, I am about to fly UA1633 from KMSP to KORD and am trying to work out where my alternate should be. Will United Airlines have a set alternate that flight 1633 will always use that I will be able to find on Google? Or does it depend on traffic, weather etc?
It actually depends on the aircraft and airfield. Air traffic dictate the diversion airfields, having a list of 3 or 4 with the captain choosing the most relevant.
For your choice, it should be one that is far away enough to not be effected by the same weather at the same time.