The Double-Decker River hits Louisiana

Flooding in Louisiana

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As Louisiana, East Texas and the Midwest floundered in floods, satellites showed a startling picture. A double-decker river is flowing up the Mississippi! Hovering over the rolling waters of the Mississippi River is a giant atmospheric river

A giant atmospheric river stretched from South Texas to New England.

Welcome to the schizophrenic nature of La Niña conditions in the Tropical Pacific. Typically, when La Niña conditions dominate the Pacific, we see more extreme weather – more droughts and, strangely enough, more flooding. Rainfall patterns are compressed and concentrated, so that areas that do receive rainfall, frequently receive way too much rainfall. When this happens on a year like this one, with unusually hot Gulf and Atlantic air masses feeding humid marine air into the river, it can create terrible floods. Parts of Louisiana and East Texas have experienced record floods and high river levels.

La Niña conditions are when the unusually cool Tropical Pacific creates extreme weather. Source: NASA

When pools of cooler water and the cooler air above them, hit warmer water, it causes storms. The cooler La Niña air meeting warm Atlantic air created a record number of July hurricanes in the Pacific. When winds were not right for spinning storms; atmospheric rivers. Thanks to the spin of the Earth, the moisture from these storms stream north and south, away from the equator (and currently over the US).

Atmospheric Rivers flow north and south from tropical storms. Source: NASA

These “rivers in the air” can be huge, thousands of miles long and 250 to 350 miles wide. A strong one carries as much liquid (in water vapor) as 7.5 to 15 times the average flow water at the mouth of the Mississippi River. They bring rain from the tropic to the rest of the world, which is good, but if they are too strong, they cause floods. If one hits the West Coast it is called Pineapple Express, while one that hits Texas is a Mayan Express. So far, poor Texas has been hit by three this year, in March, June and now. 

When an atmospheric river hits the West Coast it is a Pineapple Express. When it hits Texas and Louisiana, it is a Mayan Express.

So poor Louisiana was hit by a double-decker river—one in the air raining down and one on the ground rising up. Stay safe and share your story here.

About This Blog

Are you a weather watcher? Welcome to "Weather Whispers" by James Garriss and until recently, Evelyn Browning Garriss. With expertise and humor, this column covers everything weather--from weather forecasts to WHY extreme weather happens to ways that weather affects your life from farming to your grocery bill. Enjoy weather facts, folklore, and fun!

With heavy hearts, we share the news that historical climatologist and immensely entertaining Almanac contributor Evelyn Browning Garriss passed away in late June 2017. Evelyn shared her lifetime of weather knowledge with Almanac editors and readers, explaining weather phenomena in conversation and expounding on topics in articles for the print edition of The Old Farmer’s Almanac as well as in these blog posts. We were honored to know and work with her as her time allowed, which is to say when she was not giving lectures to, writing articles for, and consulting with scientists, academia, investors, and government agencies around the world. She will be greatly missed by the Almanac staff and readers.

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