A lightning strike alert. This I found out was delaying my flight home from Toronto's Pearson Airport last night. And likewise stranding the poor souls on the inbound plane parked not 10 feet from the bridge. So the waiting game began, with nothing happening outside other than a few drops of rain. And nothing to do but stand around and watch.
Funny that it wasn't until after the alert was lifted when I actually saw lightning in the sky. Go figure.