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Atmospheric Rivers | Pineapple Express

  • Context (IE): The recent storm that hit California was fuelled by an atmospheric river, including the Pineapple Express.
  • It marks the second atmospheric river event to affect California recently, following another system that caused significant rainfall and snow in the San Francisco Bay Area.

Atmospheric River

  • An atmospheric river is a long, relatively narrow band of water vapour that forms over an ocean and flows through the sky, transporting moisture from the tropics to northern latitudes.
  • They are formed by winds associated with cyclones and move under the influence of other weather patterns.
  • It ranges from 250-375 miles in width.
  • While many atmospheric river events are weak, powerful ones can carry extraordinary amounts of moisture.

Atmospheric Rivers

When an Atmospheric River Reaches the Land

Atmospheric Rivers

  • As the moisture-laden air moves over mountain ranges, the water vapour rises and cools.
  • This cooling results in heavy precipitation that falls as rain or snow.
  • Unlike traditional cold winter storms, atmospheric rivers tend to be warm.
  • While snow may still fall at the highest elevations, rain usually falls on the snowpack at lower elevations.
  • This rapid melting can lead to runoff, flooding, and a decrease in the snowpack needed for California’s water supply.

Uses of Atmospheric Rivers

  • Replenish Water: Essential for refilling water sources in arid regions.
  • Wildfire Mitigation: Provide rainfall to help extinguish wildfires.

Impacts of Atmospheric Rivers

  • Causes significant flooding, especially after consecutive events.
  • Trigger debris flows and mudslides in saturated areas.
  • Boost snowpack levels, crucial for water supply.
  • Impact global ecosystems and water balance.
  • Microwave remote sensing from polar-orbiting satellites has enhanced atmospheric river observations over oceans.

Pineapple Express

  • The term “Pineapple Express” refers to a strong atmospheric river originating in the tropical Pacific near Hawaii.
  • When the Pineapple Express reaches the West Coast, it can bring intense rainfall, sometimes dumping as much as five inches of rain on California in a single day.
It is named for its moisture trail extending to Hawaii’s pineapple region.


California Map

  • It is located on the west coast of the United States.
  • It shares its borders with Oregon to the north, Nevada to the east, and Arizona to the southeast.
  • California has one of the largest economies in the world.
  • It is a hub for technology, with Silicon Valley being home to major tech companies.
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