Not worried about the Lahars coming off Rainier. I don't live anywhere near it. For that matter, I'm not worried about any Lahars coming off anything. Next closest lahar producing place is Mt. Hood and I have the hills west of Portland between me and it.
The Cascadia subduction tsunami is a slightly higher possibility. I've thought it through but I don't have a clear answer about whether a tsunami of that magnitude would flow 100 miles upriver against the Columbia river. Again though, I live at about 250 feet above sea level so if the tsunami gets that high, it's because god hates me.
What seems more likely is an earthquake. Either from the subduction zone or one of the other faults in the Portland area.
re-cur-sion ri'-ker-shen n: see recursion