Friday, September 14, 2012

Long Range Lookout: Traffic Jam Over North America

This is a new section I call the 'Long Range Lookout', where we take a look at what the long range models are showing, and what it means for the future.

This is a 500mb height anomaly map for September 22nd. We can see a very well established blocking pattern across North America, with two major ridges positioned over eastern Alaska into northwest Canada. This partially extends into the western US. Another major ridge stands in the waters to the south of Greenland. These two ridges create a pattern favorable for major troughing across the south central Canada/Upper Midwest regions in response to this atmospheric traffic jam.

I marked two arrows going in a circular pattern over the area where the trough is positioned. Looking at the forecast in a few days prior to this particular image, it is almost like an assembly-line system of new disturbances being generated across central Canada that get caught in the traffic jam and are forced south into a spinning, stationary trough as is pictured above. This will enable frequent visits of unseasonably cold air into the Midwest and Northern Plains as a result of the troughs pulling down cold air from Canada.

Also, take note of a disturbance to the south of the ridge positioned over Alaska and Canada. I did draw an arrow that is directed into the Southwest. Storm systems in this position commonly will take the route I outlined, and at this time, it looks to be the only route. As a result of the ridge in the Western US, the disturbance will be forced south and make landfall in the Southwest. As is typical of an El Nino, this system will likely move through the Southern Plains, but that's when things get tricky. The question is, will the major troughing pattern be able to pull in the disturbance traversing the South, thus bringing precipitation into the Mississippi Valley? Should that happen over and over again, we could have this winter's storm track on our hands. However, the probability of such a strong regime of blocking is low as far as lasting long goes.

Notice the red circle marked off the Southeast. This is a feature you should all get to know and love, especially the Midwesterners. This ridge can strengthen during the winter, and push into the Southeast. If the ridge pushes into the Southeast, storms can be directed on a northward path, following the track of the Chicago Blizzard in 2011. A glance at forecast hours near the image above shows the ridge south of Greenland pressing south, resulting in another major trough pushing the circled ridge west. If this would play out in the winter, this could have very interesting implications for those in the Midwest and Ohio Valley, as far as snowfall potential goes.

That's this evening's Long Range Lookout. As time goes on, I hope to expand this to include more forecasts and more notes that can be taken from said forecasts.

Have a great evening!


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