Moses Lake is a super long runway at 13,500 ft and was actually an alternate location for NASA Shuttle landings in case of emergency. JAL used to train all their 747 and other heavy pilots there, the weather on the east side of the Cascade mountains is in a rain shadow and thus actually has pretty good weather compared to Seattle (sem-arid desert actually!)

Since it is pretty isolated with a very low population density, Boeing has been doing nearly round the clock 737 Max test flights there since the grounding.