"when their only fight is to New York and leaves just after midnight. I mean, who in their right mind wants to fly that early/late?"
Again, that's just what I was talking about earlier. It's a repositioning flight.
If you figure that flying starts about 6AM on the east coast, that's 3AM in the West. So, any transcon stuff from east to west can leave at 0600 and get to the west by mid-day local time. So, for the first few hours of the day, all traffic is moving west.
The other direction, from west to east, in order to get to the east coast by a reasonable time (e.g. 11 PM
), you have leave in the early afternoon Pacific time. So, the last "reasonable" flight out from SEA
, etc. heading to the east coast would be 3ish. After that, people are going to get in darn late.
With the flight you mentioned, it likely comes to SEA
from somewhere else - either on the West Coast (e.g. LGB
) or as a trans-con. To make up for that initial batch of aircraft moving west in the morning, they have to get the same number of planes back to the east coast... some of them happen to be overnight. That way, they are ready to start migrating west in the morning.