La Niña Brings Rain, Avalanches, Floods, Tornadoes to the U.S.

This animation from NOAA’s Earth System Research Laboratory shows an atmospheric river event in January 2017. Atmospheric rivers are relatively narrow regions in the atmosphere that are responsible for most of the horizontal transport of water vapor outside of the tropics.

by Natasha Lasky, ODP Staff Writer

This March will continue to bring more severe weather to the United States. An atmospheric river event — the “Pineapple Express” — is forecast to induce a rainy season in Washington and Oregon, as well as an increased risk of avalanches in the Pacific Northwest. 

As the Pineapple Express moves from the ocean to the land, over mountains, it creates rain and snowfall,  and even flooding. High winds, high tides, and river flooding will likely occur, while winds will consistently range from 15 to 25 mph, reaching as high as 40 mph in the next 72 hours. These winds could lead to power outages, an especially grave concern given that there are still thousands of people without power in Oregon from a storm that hit a week ago.

Meanwhile, tornadoes may be more common in early spring this year, as a result of continuing La Niña conditions. 

Why This Matters: The world suffered a record 50, billion-dollar weather disasters in 2020, the most billion-dollar disasters ever recorded, according to insurer Aon in its annual report

Atmospheric rivers cause an average of $1.1 billion in flood damages yearly — just in the western U.S. alone, In coastal northern California, these atmospheric rivers caused over 99% of damages

Likewise, tornadoes with their sporadic nature strike quickly and inflict maximal damage. Last year, a violent derecho in the midwest caused $11 billion of damage, caused by tornadoes, hail, and other severe thunderstorms.

La Niña Hits Hard: Both the Pineapple Express and the increase in tornado conditions can be traced back to the continuing La Niña conditions this spring. 

The Pineapple Express is a type of atmospheric river —a long band of moisture in the atmosphere that brings water from the tropics to higher latitudes. They can bring up to fifteen times the volume of the Mississippi River. La Niña conditions like the one this year, tend to induce more severe and frequent atmospheric river storms in the Pacific Northwest. 

Meanwhile, La Niña causes the jet stream to move northward, which develops thunderstorms further north and west, creating more potential for tornado outbreaks. La Niña also forces wind closer to the ground to strengthen, which makes it easier for tornadoes to form. 

There’s evidence that suggests that La Niña conditions may grow worse as a result of climate change, because the warming world causes more moisture to be evaporated from the oceans into the atmosphere, providing more fuel for storm systems. This may mean that this spring of severe weather may not be the last. 


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