What's a Pineapple Express Anyway?

Drought-stricken California will be inundated with a foot or more of rain over the next several days, thanks to a group of storms riding the so-called Pineapple Express.

“Pineapple Express” is an actual, though somewhat informal, term meteorologists use to describe slender currents of air – also known as “rivers” — flowing in the atmosphere.

Like the name implies, the pineapple express travels in a southwest to northeast flow from the tropical Hawaiian Islands, driven by the jet stream.

While California experiences mild, dry conditions from spring to fall, the Golden State can receive very heavy rain over several days during the winter as the jet stream shifts.

Rainfall from systems like the pineapple express are vital sources of precipitation for large portions of the West Coast — and California in particular. These systems can deliver up to half of the region’s annual precipitation in any given year.

Credit: NASA

Credit: NASA

But while these drought-busting systems can bring much-needed rain, the warm air accompanying a pineapple express can also cause flooding and melt snow in the mountains. Heavy rain from a pineapple express can also uproot trees and spell disaster for areas susceptible to mudslides once the ground becomes saturated.

This latest Pineapple Express is expected to bring the heaviest rain and fiercest winds that parts of northern California to the San Francisco Bay metro region haven’t seen in five years. These extreme conditions are causing travel and flight delays, and will likely cause power outages. Weather conditions may force some communities to evacuate.

If you approach a flooded roadway, it is best to “Turn Around, Don’t Drown.” Be sure to stay tuned to local officials for updates and instructions!

Stay Safe!

The WeatherBug Team

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