I would expect a firm decision by mid-morning Monday. By then they should have a close enough track. Unless it totally falls apart, I'd expect some kind of storm and with it some disruptions, especially from the winds, which seem to be a part of ALL forecasts.

With ORD as their primary hub, I'm not sure how UA will handle a slow-down or shut down of several days. You might try calling now and asking about changing flights to avoid ORD, especially on Tuesday or Wednesday. Those seem to be the worst on everyone's list. UA may allow some preemptive changes now.