Nine whole weeks?
Sounds more like "temporary" service as opposed to "seasonal" service.
Its Canadian season.
ever since Air Canada started shafting their customers, the canadian passengers spiked to an absolute insane level at seatac. Seatac park told me they were 100% full due to a massive influx of canadian plates...along with a bunch of other lots.
If people are actually willing to drive 4 hours into another country to save money on airfare, expanded bellingham service to make use of their slightly underutilized portland hub seems to make perfect sense to me.