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Mysterious Atmospheric River Soaks California, Where Megaflood May Be Overdue

The views expressed are those of the author and are not necessarily those of Scientific American.


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An atmospheric river (thin yellow band) feeds torrential rain into northern California on Nov. 30. Image courtesy of NOAA

Northern California is experiencing the first days of what weather forecasters are warning will be a long series of torrential rainstorms that could cause serious flooding across the northern one-third of the state. The relentless storms are being driven by a feature in the atmosphere you have probably never heard of: an atmospheric river.

Oh, and another atmospheric river created the worst flooding since the 1960s in western England and Wales this past week, where more than 1,000 homes had to be evacuated.

An atmospheric river is a narrow conveyor belt of vapor about a mile high that extends thousands of miles from out at sea and can carry as much water as 15 Mississippi Rivers. It strikes as a series of storms that arrive for days or weeks on end. Each storm can dump inches of rain or feet of snow. For more details, see this feature story that Scientific American has just published, written by two experts on these storms.

Scientists discovered atmospheric rivers in 1998 and have only recently characterized them fully enough to allow forecasters to warn of their arrival. They can strike the west coasts of most continents, but California seems to be a prime target. As many as nine small atmospheric rivers reach the state each year, each lasting two to three days, including the famous “pineapple express” storms that come straight from the Hawaii region of the Pacific Ocean. Ironically, although the storms are dangerous, they are also vital; they supply 30 to 50 percent of California’s rain and snow—in the span of about 10 days a year.

Megaflood Overdue?

The real scare, however, is that truly massive atmospheric rivers that cause catastrophic flooding seem to hit the state about once every 200 years, according to evidence recently pieced together (and described in the article noted above). The last megaflood was in 1861; rains arrived for 43 days, obliterating Sacramento and bankrupting the state. The disaster is largely forgotten, but the same region is now home to more than six million people. Simulations of a 23-day storm there indicate that more than $400 billion of damage and losses would occur, far surpassing the $60 billion estimates for Hurricane Sandy’s effects. New research also shows that climate change may make these storms more likely to occur.

You may begin to hear the term “atmospheric river” more often. The Weather Channel is using it, in quotation marks, in warnings for northern California, as well as the coasts of Oregon and Washington. And some popular media are beginning to adopt the verbiage as well.

Mark Fischetti About the Author: Mark Fischetti is a senior editor at Scientific American who covers energy, environment and sustainability issues. Follow on Twitter @markfischetti.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. outsidethebox 11:30 am 11/30/2012

    “New research shows that climate change may make these storms more likely to occur”.

    My respect and admiration for SA used to know no bounds. And now you get statements and articles like this. No data, no proof, not even a reference to an actual study. I’m not even saying the idea is not correct. I am saying it is a sign of intellectual laziness on the part of the author.

    Link to this
  2. 2. SenorDante 11:52 am 11/30/2012

    @outsidethebox – You’re reading a blog entry the purpose of which is to generally introduce the concept. If you’ll kindly click the link to the feature article you’ll find references listed at the end of the article.

    Link to this
  3. 3. julianpenrod 12:35 pm 11/30/2012

    “Atmospheric rivers” are described as only about a mile high and massive conveyors of water vapor. And they have gone unrecognized even after all the decades of weather balloons, rockets and airborns observation? That is questionable to the point of being non credible.
    INteresting, and probably important, to note is that they described “atmospheric rivers” are being “discovered” in 1998. 1997 was the year chemtrails were first acknowledged being seen, by Art Bell. Interestingly enough, in California, the area this article suggests may be particularly hardest hit. 1998 was also the warmest year on record; the year of the largest year-to-year drop in Arctic sea ice coverage; and the beginning of the unnaturally massive spate of hurricane seasons which included the unprecedented 2005 season, which saw events such as Hurricane Katrina. It’s often suggested that that was the year chemtrails began. In fact, it appears chemtailing has been ongoing since the beginning of the age of jets, around 1950. 1997 seems to be the year chemtrail chemicals became so saturated in the atmosphere that new loads precipitated out to form chemtrail lines! The number of tornadoes in the U.S. also exploded in number from a fairly constant 180 per year, starting in about 1952 to about ten times as many today. 1952 is also when the first new cloud species in a long time was announced, the cirrus intortus. The next new cloud species, the undulatus aspiratus, was announced only in the past few years, after chemtrail chemicals saturated the atmosphere.
    In fact, climate change is occurring, but it’s not the result of industrial pollution. It’s being deliberately caused by chemtrail contamination of the air.
    Supporters of lies cannot rely on their “point of view” to be able to argue from it. As a result, defenders of untruth often rely on non argument techniques to counter truths. Like non justified dismissiveness, contempt, arrogance, viciousness, mockery, vulgarity. No New World Order favoring defenders of the “official story” will address what I said with anything but non argument methods.

    Link to this
  4. 4. jobjobx 1:08 pm 11/30/2012

    Fascinating stuff.

    However, I’m not sure why the article speaks of it being “overdue” — when a Las Vegas roulette wheel gives “red” five times in a row, is “black” then overdue?

    I would think these things are exponentially distributed (like roulette outcomes) rather than cyclic. Unless there is evidence for cyclicity, it would be misleading, and a bit sensationalist, to speak of it being “overdue”.

    Link to this
  5. 5. Charles Hollahan 1:50 pm 11/30/2012

    I knew I had seen this before, the pineapple express had to be one of these things. I worked in the nearshore environment in the Pacific Ocean in Southern California and I used to get up in the morning at 5 AM and check the wind speed online. It would be blowing 25 kts (that’s a lot at 5 AM) when one of these things appeared. We received less rain than areas further to the South during these events but coastal areas stripped of vegetation by fires had so much mud go into the sea that it was really miserable even when the wind wasn’t blowing.

    Well, maybe the drought in the mid-west will finally be broken by these extreme weather events. I won’t say anything about Sacramento…

    Link to this
  6. 6. Cramer 2:17 pm 11/30/2012

    jobjobx, I think you mean “independently distributed.”

    You are correct, “overdue” might be a bad choice of terms. An average of nine of these “atmospheric river” storms hit California each year. What are the odds of many different maximal conditions forming at a one time for one of these storms to become a megastorm? Can you be sure that there is nothing cyclic? Like Pacific decadal oscillation, for example?

    Sandy was greatly enhanced by high tide — that’s a cyclic component.

    Link to this
  7. 7. priddseren 4:11 pm 11/30/2012

    1998 is when these rivers were discovered, so they could not have been included in the prophetic and perfect climate models from the 90s, those same models that predicted 10 degrees of more heat than actually happened. I am just making a guess here but 15 Mississippi rivers worth of water floating around in an atmospheric river probably has some sort of effect on the climate, likely ignored by climatologists, as they ignore everything else that doesn’t fit their theory, such as ignoring clouds until a couple years ago. .

    I also live in LA and we have already experienced long duration storms. It was only a decade or so ago, a storm hit LA that produced rain nonstop from the end of December into February. It caused a heck of a lot of problems, was annoying and damaged a lot of stuff so why did the author note a ridiculous model for 23 days when there was a past real world event of this storm type for more days and actual data about damage, flooding costs and etc could have been reported on. At some point you climate scientists should try some real world data instead or your models. Or at least tune your model to see if it matches up.

    A few months ago, SA reported the ridiculous claim of Climate scientists the missing heat from the last decade went into he deep ocean. The article posed the question where did the missing heat go, you know the magical heat the vaunted and perfect climate models predicted from 1998 on for a decade. The scientists involved totally speculated this heat must be in the deep ocean. They admitted they have no idea, no understanding of the interaction of the deep ocean and atmosphere or anything really about the deep ocean and heat but plugged this totally unproven theory into their models and tweaked the model until it produced data they felt matched what really happened and now claim this new model is it.

    So going back to the effect of atmospheric rivers, only discovered in 1998 and therefore not in climate models, isn’t it possible the “missing” heat ends up in these rivers, the energy to keep the rivers warm, floating and moving has to come from somewhere. Then with rainfall and eventual storms that occur, the rain transfers this heat down to the planet, having a cooling effect on the atmosphere. This is in effect how an air conditioner works. Transfers heat out of an atmosphere with water. ACs dont work if there is zero humidity.

    But who am I to say anything like this. The mere fact that I proposed a theory about where the heat is going and I am not a government grant supported climatologist means I cant possibly know what I am talking about.

    Link to this
  8. 8. Charles Hollahan 9:31 pm 11/30/2012

    The pineapple express comes across the open ocean where the central gyre is warmer and picks up moisture along the way. During El Ninos the storms tend to come down the coast from the Gulf of Alaska then double back and slightly North and Easterly and they’re colder storms, often produce light snow in the coastal mountains.

    The El Nino storm can last for months at a time and I experienced the same thing during the late 1960s when huge mounds of kelp washed up on Santa Monica’s shores, the 1970s were pretty dry and the diving near Zuma Beach was great, although the water was cold as well as clear, but the 1982 El Nino destroyed the Santa Monica Breakwater, much of the pier, and the pier in Paradise Cove as well.

    The pineapple express sometimes comes out from way beyond Hawaii and we got lots more wind in Santa Barbara than rain. I watched the satellite loops of the water hitting Los Angeles and my friends there would be kept from working as well. At the time it was just another reason to avoid LA… this storm seems to have more energy (attached photo) and is dumping the water further North.

    Link to this
  9. 9. greenhome123 3:38 pm 12/1/2012

    finally we can get some rain. the san luis rey river by my house in Oceanside, CA has been totally dried up for the past few months.

    Link to this
  10. 10. norcalrez 1:35 pm 12/2/2012

    SO VERY GLAD to see that people aren’t as gullible anymore from reading the comments here. This is such BS. Do you know another brand new term? geoengineering of the weather. No one is buying this BS, “scientistors”.

    Link to this
  11. 11. Postman1 9:54 pm 12/3/2012

    “They can strike the west coasts of most continents,”
    Shouldn’t that include ‘in the Northern Hemisphere’?
    I’m thinking I agree with comment #1, outsidethebox.

    Link to this
  12. 12. Mrironstreet 3:43 pm 12/4/2012

    Well now we know exactly what happened to the melting ice at our poles,its just a shame theres noway to ship this water to our countries south westernstates……..

    Link to this

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