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Flip-Flop Summer Caused by Strange Jet Stream

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


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By now, if you live in the northeastern U.S. you have heard or even said the following:  “This summer has been so cool. I love it.” Or: “This summer has been so cool. I hate it.” Yet if you live in Oregon or Washington, you’ve heard the opposite: “It’s been so hot this year!”

Maybe people just like to complain? Nope. The data is in and headlines are everywhere the past few days: temperatures across the Northeast have been unusually cool, and they have been unusually hot across the northwest. Boston typically hits 90 degrees Fahrenheit on about 15 different days of the year, but so far it has only reached that mark four times. Washington, D.C. , had hit the century mark 16 times by August 15, which might sound like a lot until you learn that the average by that date is 29. Meanwhile, Portland, Ore., has sweated 90 degrees F 12 times already; that usually happens just a few times a year.

A strange jet stream is behind the flip-flop between summer conditions in the two northern corners of the country. The polar jet stream is the prevailing band of wind that blows west to east across the upper half of the U.S. in summer. (There is a subtropical jet, also, that typically crosses northern Mexico). We often see the jet stream depicted on TV weather reports—that big, wavy line across the U.S. and Canada that bends south then north then south again. Low-pressure weather systems, sometimes called cold fronts, ride along the jet stream, bringing us much of our daily weather. But this summer the polar  jet steam seems to be somewhat flattened out, and it’s been in that position more than usual. Meteorologist Dylan Dreyer of NBC’s Today show summed it up nicely in a short segment I happened to see this morning. Watch the video below, if you like.

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Data from the National Weather Service, and headlines from numerous states, reflect the flattened jet stream Dreyer shows in the video. In addition to the Northeast, middle-American cities from Chicago to Dallas and even further west to Denver have all had fewer hot days. So what could make the jet stream flat? A combination of forces in the atmosphere and the Pacific Ocean come into play day to day, but those factors themselves may be changing due to climate change. Several studies published in the last two years in leading journals have indicated that the jet stream’s waviness may be becoming more extreme, and it may be getting stuck in those patterns for longer periods of time.

In the winter, “extreme” often means an even larger, sharper curve than usual—bringing the infamous polar vortex down from the Arctic, for example. But this summer, extreme seems to mean flatter. A study led by S.-Y. Simon Wang at Utah State University, published in April in the journal Geophysical Research Letters, noted that the extremes have been made more likely because of climate change. As I’ve written before, our changing climate is not so much “global warming” as it is “global weirding.”

We will see, of course, whether this weather pattern holds up for the rest of the summer. But it’s already August 18, and the 10-day forecast for my home town in Masachusetts shows nothing but high temperatures in the 70s.

Jet stream image courtesy of NOAA
Video courtesy of NBC

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. alcasey 9:40 am 08/19/2014

    Nicely done Mark. The weirdness that happens when a system transitions from order to new order is called Chaos — as in Chaos Theory. The principle at play here is observed in all things that transition from one stable state to another. Chaos is the gauntlet that the changing process must go through. Everything from spring-cleaning your house, to smashing a granite rock, to reorganizing corporate management, to climate change must go through the gauntlet. This means that things will become unsightly, unstable, uncomfortable and uncertain for a period of time. This is also seen in binary computing circuits; when a gate makes a rapid switch from zero to one – or vice versa – the point at which the corresponding voltage change occurs there is a ringing effect; the voltage oscillates for a time until it settles into its new state. There is no way to escape it – climate change is no exception. The questions that are begged are; what will the new stable-state settle into, will it sustain human life, and when will we get there?

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  2. 2. litpunk 11:28 am 08/19/2014

    Out of curiosity, should all the arrows indicating jet direction be pointing the same way? Don’t the different flows run in opposite directions…

    Link to this
  3. 3. SJCrum 7:44 pm 08/19/2014

    By the way, the reason the jet streams have an S-curve pattern is because the more southern loop of the jet stream is pulled toward the northern polar ice, AND the next morning the colder jet stream air is then pulled toward the southeast rising sun temperature.

    The reason the air has been cooler this year is because the polar ice is diminishing.

    By the way also, that is actually a very good thing, and if the cap ice is gone that would create jet streams that are very parallel to the equator and we would have far milder weather and temperatures. And no, the ocean levels wouldn’t rise at all, which can be easily found as fact by simple testing first. There also wouldn’t be any hurricanes or tornadoes ever again.

    As for why the temperatures were hotter in the northwest, the mountains blocked the further south jet stream there and that colder situation attracted more heat from the equator south.

    Link to this
  4. 4. MikeB 10:35 am 08/20/2014

    “The data IS in…”
    Have grammarians officially surrendered?

    Link to this
  5. 5. Dr. Strangelove 10:15 pm 08/21/2014

    “A study led by S.-Y. Simon Wang at Utah State University, published in April in the journal Geophysical Research Letters, noted that the extremes have been made more likely because of climate change.”

    A meaningless claim. The climate is dynamic and always changing. A climate that is static and without extreme weather phenomena is a hypothetical unicorn. We dream about it but it doesn’t exist in reality. I grant it exists in models.

    Link to this

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