Hmm.. weird. I would have guessed it would have taken a lot of snow in Portland to get stuff to close, but you're used to more rain then snow, I guess.
Here in Upstate New York, there are a few schools in the hills that close at the first inclings of snow, but, for the most part, schools don't close unless there is a LOT of it. Back when i was in middle school, I do remember them closing school one day cause it was too cold out (the busses wouldn't start). It was around 30-40F below. Other then that, it just takes lots and lots of snow.