Boom Boom Bellevue

A few minutes ago there were two huge booms loud enough to shake the house, about a second apart.  Nothing visible looking around outside the house, but sirens in the distance and one firetruck raced down our street on the way to somewhere else.  Still no idea what it was.  Am scouring local news sites, twitter, etc, but nothing yet.  But it was enough to end quiet time in bed reading, and I’m getting up.