Surprised this didn't get mentioned. Snow at Narita caused cancellation of probably 90% of all flights.
I can vouch that Terminal 1 looks like a giant boy scout campout. There are well over 1000 people in the landside area. While, stunningly, the airlines haven't bothered to bring in extra personnel to start with the rebookings, the airport authority has been wonderful, providing blankets, boxes (to break open and lie on), water, and crackers and other snacks.
I suspect some folks will not be leaving Japan today either. I have encouraged those near me to use Skype on my laptop to call the airlines and reschedule now, rather than waiting for the desks to open in the morning.