It was my understanding that this is more of a seasonal thing than on a day to day basis. That is, during the summer, southern California uses a large amount of

It was my understanding that this is more of a seasonal thing than on a day to day basis. That is, during the summer, southern California uses a large amount of electricity for climate control, and so power is transferred along the Pacific DC intertie in a north -> south direction. In the winter, electricity usage in the north is devoted to heating, whereas in the south temperatures are mild. The result is that power is moved back up the intertie from south -> north. In the spring, snowpack melt refills the reservoirs in the hydroelectric system, allowing it to be ready to provide power to the south again once temperatures start to climb.