ScienceShot: California Takes a Ride on the 'Pineapple Express'

Dick writes about Earth and planetary science for Science magazine.

How do you get 4 meters of snow in the Sierra Nevada of California over one weekend? Stand in the path of the “Pineapple Express.” This 7000-kilometer-long jet of moisture-laden air extending from near Hawaii can deliver 50 million liters of water per second to California. In recent days, this jet delivered 25 centimeters of rain to some areas, with the mountains getting their tropical moisture as meters of snow. The pump driving such flows is a North Pacific storm whose cold front arcs down into the tropics. A narrow river of moist, tropical air (diagonal band of cloud) rushes north and east just ahead of the front until it hits California, often for days on end. Flooding and mudslides often follow.

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