Aug 15, 2016
As Texas, Louisiana and the Midwest flounder in floods, satellites show 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 has NOAA forecasting floods from Texas and Louisiana to the Midwest. (Day 1-3 and 4-5 maps)
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, with unusually hot Gulf and Atlantic air masses feeding humid marine air into the river, it can create terrible floods.
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 hurricanes and tropical rains. When winds are not right for spinning tropical storms it creates atmospheric rivers. Thanks to the spin of the Earth, the moisture from these storms stream north and south, away from the equator.
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 – 350 miles wide. A strong one carries as much liquid (in water vapor) as 7.5–15 times the average flow water at the mouth of the Mississippi. 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 and areas around Houston and in the Midwest are trapped between double-decker rivers – one in the air raining down and one on the ground rising up. Meanwhile cotton and corn growers wait to see how these storms and floods will affect the price of their crops.