it's not just going to erupt out of the blue while you're climbing it.
Happened to me once. Got some good photographs though.
Rainier is probably heavily monitored, so the chances of it erupting by surprise is fairly low, but it does happen on occasion. All the volcanoes in New Zealand, for example, are heavily monitored, but Mount Tongariro had a surprise eruption last year that was unexpected. There were a few small earthquakes (which are very common there), but it erupted out of the blue and unexpected to scientists.
According to volcanologist it is possible that Rainier could erupt unexpectedly too:There may be little or no advance warning: Studies by U.S. Geological Survey (USGS) scientists show that at least one of Mount Rainier's recent large landslide-generated lahars may have occurred when the volcano was quiet and not providing the warning signs typical of a restless and erupting volcano. In such a rare case, the only warning could be a report that a lahar is already underway.http://geology.com/usgs/rainier/
Expected or not, when Rainier does go, it's going to wipe out a lot of homes and be a large scale disaster. The source above gives a 1/10 chance of a large lahar within an average human lifespan.
Anyway, I'm from Washington. We left before St Helens blew, but went back just after the eruption. As a six year old kid (it happened a month before I turned 6), I remember scooping up volcanic ash and viewing the destruction. It was rather awe inspiring for a little kid. St Helens is just a little baby volcano in comparison to Rainier.
Maybe this is getting a bit off topic though.
I'm slow and fat. Unfortunately, those are my good qualities.