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.

When an Atmospheric River Reaches the Land

• 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.

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.