River in the Sky, Rain and Snow on the Ground!

January 29, 2016
California Flood

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Watch overhead! A river may be coming at you.

If you are in California, you will welcome the giant atmospheric river that brings rain to your parched state. In the East, you might not be so grateful. One of those rivers created Snowmageddon in 2010 and, really, who needs more snow?

When cold fronts carry rivers of tropical water vapor north, it brings rain, sometimes too much rain. Source : NOAA

An atmospheric river (AR) is a band of tropical water vapor caught on the edge of a cold front and carried toward the poles. These 250 to 350 miles-wide bands carry as much as 300,000 tons of water, 7 to 15 times as much as the mouth of the Mississippi River. When they hit land, rain and snow sometimes causes landslides, major floods and general misery. Ask Californians about the AR at the end of February. They were pleased to see the rain and snowfall (except for some of the damp visitors to the Oscars) but not with the power outages, accidents, and mudslides.

The rains and floods of California this February and March are due to atmospheric rivers. Source: FEMA

We are only beginning to understand these rivers. Discovered by Reginald Newell and Yong Zhu in the 1990s, they were originally connected with West Coast flooding, particularly the infamous “Pineapple Express” that flows through Hawaii. We now know they have a central role in the global water cycle. On any given day, these relatively narrow bands of water vapor account for over 90% of the movement of tropical moisture north and south. Most of the time, they bring warm, welcome rainfall in moderate amounts.

The good news is that scientists are increasingly able to warn people where and when the worst atmospheric river floods or snows will hit. They have also learned that these AR events can happen throughout the world. The floods that have been hitting England this winter are river storms. Some of the worst Nor’easters, like 2010’s Snowmageddon were caused by an atmospheric river flooding the chilly East Coast.

Snowmageddon, When an atmospheric river hits the East Coast in winter, it can create a Nor’easter. Source: NOAA

So look up in the skies. It’s a bird, a plane—no—an atmospheric river coming at you. You may not enjoy it, but the flowers this spring will be grateful.

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 articles. 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.

Reader Comments

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I heard we're going to have a

I heard we're going to have a summer el nino this year. It'll be good news for the people in California who are struggling with the devastating drought. I think the el nino that never developed has really hurt them because after a la nina in 2012 they were dealing with wildfires and record heat ever since. They need the rain much more than anybody else.

However, hopefully the el nino doesn't bring any more unusually chilly and wet weather here in the southeast. Do you think this summer will turn out to be another non-summer? Because last summer we had way too much rainfall and with the record rains, it held temperatures down much like 2009. We could never dry out long enough for us to have any typical summer weather. An el nino will be very good for drought-stricken California but will it give us a break at all? After a cold and snowy winter, we're all ready for a nice warm summer on the east coast.

Most, but not all, El Ninos

Most, but not all, El Ninos bring rainfall to California, especially in the winter. There is a wierd Central Pacific type that doesn't bring enough rain. Hopefully the upcoming event will be a normal event.

If the east has a cool summer, it will be more due to the lingering cold from the frozen Great Lakes, not an El Nino.


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