Wild Week: Winter Storm and Heat Wave Whipsaw US

September 28, 2019

The new normal is no normal.

I produced the video above in the spring to explain the wild weather patterns that the US heartland had been seeing over several months.
It’s happening again this week.


Historic snow and a heat wave? That’s what a downright loopy jet stream pattern is bringing to large parts of the United States.

Parts of the Northern Rockies are bracing for what the National Weather Service in Missoula, MT is describing as an “historic winter storm this weekend,” with up to five feet of snow forecast. (Click on the graphic above for details.)

Although this part of the United States is no stranger to early autumn snow, it’s not usually measured in feet.

Meanwhile, parts of the U.S. East Coast are continuing to experience temperatures well above normal for this time of year — and conditions are forecast to heat up even more, potentially to record-high levels next week.

With a stubborn “heat dome” parked overhead, the Southeast has already been enduring one of its hottest Septembers on record. And the strength of the dome is forecast to intensify next week to a point that occurs just one day every 10 to 30 years during this time of year, according to an analysis by meteorologist Rob Elvington of WAAY TV in Huntsville, AL

This graphic helps explain what’s going on:

Big bends in the jet stream are tied to extreme winter weather in the Northern Rockies and possibly record-breaking warmth in the Eastern United States. (Background image: earth.nullschool.net Annotation: Tom Yulsman)

The orange line traces the forecast path of the jet stream for Sunday, Sept. 30. (I pulled that forecast on Friday the 27th — it may have changed a bit by the time you’re reading this.) That path is, in a word, all loopy.

To be more precise, it features big north-south bends. And it’s those bends that have formed the set-up for the weird weather extremes.

Note how the jet stream plunges in a deep southward bend over western Canada and the northern U.S. Rockies. That is allowing cold air to drop south.

The big dip in the jet stream has also energized a low pressure system that began near the Four Corners region. Add in copious moisture the loopy jet is helping to pump to the north, and you have, in the words of Washington Post meteorologist Matthew Cappucci, “a virtual snow-making machine as the ingredients gel Saturday night and Sunday.”

Meanwhile, see how the jet stream bends far to the north above the Great Lakes and Maine? That is allowing very warm air to invade from the south. The heat dome sits within that persistent upward bend.

Back in May of this year, wild weather contrasts ranging from violent thunderstorms to abnormal cold and snow were gripping large parts of the United States. At the time, I reported on links between a wavy jet stream and these extremes:

As humankind’s emissions of heat-trapping greenhouse gases have warmed the planet, the heating has not been uniform. Warming in the Arctic has been at least twice as pronounced as in the lower latitudes. This means the difference in temperature between the regions is less than it once was.

Mounting scientific evidence shows that this has caused the jet stream to behave more and more like a lazy stream flowing across the plains, with an increasing frequency of persistent big meanders

That behavior has been linked by researchers to extreme wintry weather during the cold months, and dramatic heat waves during the summer. But the linkages during spring and fall are not all that clear.

Overall, emissions of greenhouse gases into the atmosphere have caused increases in high temperature extremes and extreme precipitation events around the world, according to the most recent U.S. National Climate Assessment. And the United States itself has not been immune to that trend. Far from it.

Michael Mann in Scientific American:

During the extreme events I noted, the jet stream acted strangely. The bends went exceptionally far north and south, and they stalled—they did not progress eastward. The larger these bends, the more punishing the weather gets near the northern peak and southern trough. And when they stall—as they did over the U.S. in the summer of 2018—those regions can receive heavy rain day after day or get baked by the sun day after day. Record floods, droughts, heat waves and wild fires occur.

My collaborators and I have recently shown that these highly curved, stalled wave patterns have become more common because of global warming, boosting extreme weather. But we predict that the rising severity may level off for the next several decades. That may sound strangely “good”—the bad spells will continue, but at least they will not get worse. We also predict that the extreme events will start becoming much more severe, beginning around 2050 or so—particularly in summer. Threats to people’s health and safety will increase, storm damage will get more extensive and crops needed to feed a rising population will be ruined.

How do we know? Wave mathematics and quantum mechan- ics tell us. Yes—the mathematics that characterize the behavior of electrons at the smallest scale help us describe the behavior of our atmosphere at global scales. They indicate that the rise in dangerous weather, the coming plateau and the subsequent surge are driven by a curious trade-off between greenhouse gas concentrations from fossil-fuel burning and sulfur pollution from industrial smokestacks. And that trade-o raises the question of whether cutting emissions will prevent the jet stream from wreaking havoc.


4 Responses to “Wild Week: Winter Storm and Heat Wave Whipsaw US”

  1. rhymeswithgoalie Says:

    It isn’t even silly to warn Ireland against the remnants of Hurricane Lorenzo.

  2. redskylite Says:

    “Hurricane Lorenzo rapidly strengthened into a scale-topping category five hurricane on Saturday evening, with maximum sustained winds reaching an incredible 160 MPH. This breaks the record for both the easternmost and northernmost category five hurricane ever recorded in the Atlantic Ocean.”


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