I was a kid, but I remember that day crystal clear.
I was playing in my back yard in Richland, WA with a handful of Star Wars action figures. I remember VERY distinctly looking at Darth Vader's face up close (My Mom had just bought me Darth Vader the day before for my birthday). As I was studying the intricacies of his helmet, the boom went off. I have that moment locked in my brain forever. It sounded like a sonic boom, which wasn't entirely an uncommon thing to hear in the skies back then, so I figured that's all it was.
It wasn't until a little bit later (maybe 40 - 60 minutes or so) when my Dad was driving us to a "rock and gem show" at the local shopping mall in Kennewick. That's when the purple, rolling clouds started coming overhead. I was the first in the car to say "That's no storm... That's not normal... I bet that mountain blew". (The Northwest kinda knew some sort of eruption was coming, but NOBODY expected the whole mountain to explode!) When we got to the mall, everybody was huddled around radios that some of the rock/gem vendors had. It was surreal. My Dad started making a makeshift secondary additional air filter out of socks so we could get our car back home without sucking up the ash that was by that time raining out of the sky. Our cat was outside hiding under the bushes and didn't make it... We found her dead a couple of days later unfortunately.
The ash hung around the region for ages. I remember playing baseball and for YEARS if you hit the ball into this row of arborvitae trees in the outfield a white ash cloud would puff out of them and all of the parents would start yelling at the kids not to breath the stuff in.
Not many kids out there with childhood memories involving a freakin' volcano, haha!