An extreme weather system known as a “pineapple express” is headed for the upper northwestern United States. The strangely named system is expected to dump rain and snow over much of the upper west coast from Sunday through Tuesday, according to the National Weather Service. The phenomenon is known as an atmospheric river which is formed when intense moisture becomes trapped in the upper atmosphere. Systems that are originate near Hawaii are all known as pineapple express systems. The system is also expected to produce high tides, high winds and an increased chance of river flooding.