The Omega Block

November 12, 2014


omegaJet stream weirdness happens all the time Lots of historical examples of this kind of thing. This one even has a name – an “Omega Block”, after its distinctive curved shape, reminiscent of the Greek letter.

That said, a growing body of science is developing that suggests the jetstream is getting “stuck” more often – jammed into extreme configurations that stay around for long periods of time, and cause extremes of weather over large areas.  Last year’s Polar vortex is a good example.


The main system that helps determine the weather over Northern Europe and North America may be changing, research suggests. The study shows that the so-called jet stream has increasingly taken a longer, meandering path.

This has resulted in weather remaining the same for more prolonged periods. The work was presented at the annual meeting of the American Association for the Advancement of Science (AAAS) in Chicago.

The observation could be as a result of the recent warming of the Arctic. Temperatures there have been rising two to three times faster than the rest of the globe.According to Prof Jennifer Francis of Rutgers University in New Jersey: “This does seem to suggest that weather patterns are changing and people are noticing that the weather in their area is not what it used to be.”

The meandering jet stream has accounted for the recent stormy weather over the UK and the bitter winter weather in the US Mid-West remaining longer than it otherwise would have.

“We can expect more of the same and we can expect it to happen more frequently,” says Prof Francis

So, while extreme cold descended over the eastern US, large parts of the arctic, and the rest of the world, were warmer than normal.  Predictably, we expect the usual, “I’m cold, what happened to Al Gore’s Global Warming” snickering on Fox News.  Noting this – The  National Journal picked up on my Polar Vortex video last year, calling it “The One Video to Shut Down Climate Deniers”:

I had discussed the issue in interviews with several more scientists at last year’s American Geophysical Union Fall Meeting in San Francisco, which resulted in this piece.


I wrote about the Omega Block back in April, when it helped usher in a four-day tornado outbreak in the Southeast. Blocking patterns like this are a recipe for extreme weather because they essentially force huge masses of air to stay put for up to weeks on end, forcing the jet stream to take unlikely routes around them. The result? A disruption in the normally orderly west-to-east flow across America, and an increased chance of weird weather. Anomalous atmospheric setups like this week’s are at the cutting edge of climate change research. Though winters as a whole are getting warmer, they may also be getting more extreme.

And the temperature extremes this particular pattern will produce are nothing short of breathtaking. In Great Falls, Montana, Tuesday’s high temperature is expected to top out at a balmy -1 degree Fahrenheit—nearly 50 degrees below normal. Meanwhile, Barrow, Alaska—the northernmost city in the United States—will spend most of the week some 20 degrees above normal, with highs of about 30.

Decoded Science:

After passing Japan, Super-Typhoon Nuri transitioned into one of the most powerful extra-tropical storms on record, with a central pressure of 924 mb. Nuri has been absorbed by the persistent low pressure feature over western Alaska, with an accompanying ridge (high pressure) over the western US and adjacent waters.

Conforming to the predominant wavelength, another dip in the jet stream over the eastern US has become more pronounced.

The result of all this is that a lobe of the polar vortex, which normally resides over Hudson Bay, will camp in south-central Canada, with its influence pervading the eastern US from the Rockies to the Atlantic coast and deep into the south.

As large features in the pressure field become amplified like this, they tend to move very little. The high pressure becomes an omega block and the dips in the jet stream become closed lows. The result will be a long period of blustery weather in about the same places that suffered under last winter’s brutal conditions.

Important to remember – though just about everyone agrees that the jet is behaving strangely, not everyone agrees on the cause.  I recorded dueling interviews with Dr. Jennifer Francis of Rutgers, and Dr. Kevin Trenberth of National Center for Atmospheric Research, each of whom has a different take on how climate change is affecting big atmospheric circulation.




5 Responses to “The Omega Block”

  1. rlmrdl Says:

    Brilliant. At last the climate debate is starting to look like people respectfully disagreeing about the mechanisms instead of the recent moral panic versus hair-on-fire language that is sometimes needed even to get a mention on mainstream media.

    Still, while I hugely respect the work you are doing, this is what needs to make the shift to MSM. And yes, I get that any discussion at this level will glaze the eyes of the reporters and editors trying to dumb it down for their anaesthetised audiences.

  2. dumboldguy Says:

    Interesting that no one seems to want to comment on this post. Sitting here in VA as the polar vortex air arrives (with some snow) and temperatures drop to mid-January levels. I’ve been on this planet for many years, and this recurring “Omega” pattern is a new one—-it’s fascinating to look at these maps and realize how large the moving air masses are and how extreme the temperature anomalies.

  3. Peter —

    Just a head’s up… Francis is next on Schmidt’s radar.

  4. […] looking around on the internet for a while, trying this search term and that, and finally found an article explaining that yes, stationary high pressure zones, caused by an erratic jet stream ARE the major […]

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