Wednesday, November 5, 2014

Cold Times Look Like They're Coming To Eastern Half of U.S.

This huge typhoon in the eastern Pacific Ocean
could help create a nasty cold snap in the eastern
United States next week.  
Many of us living in the eastern half of the United States have been hoping the upcoming winter won't be as cold and stormy and damn persistent as last winter was.

I can't speak for the entire upcoming winter, but it looks like we're going to be off to a cold, early start to winter.

There's a few factors driving this. The most immediate one is Typhoon Nuri, out in the Pacific Ocean.

You wouldn't think a typhoon many thousands of miles away would make Chicago or Buffalo cold and wintry, but it will.

Nuri is heading north and will turn into a very, very strong storm out in the Aleutian Islands southwest of the Alaska mainland.   In fact, it will probably be one of the strongest storms ever observed in that neck of the woods.

That's still thousands of miles away from the eastern United States, so how is what will become Ex-Nuri make us cold.

Easy. The big storm will help create a big ridge of high pressure along the west coast of North America. That will create a corresponding southward dip in the jet stream further east, toward central and eastern North America.

The southward flowing jet stream east of that Nuri-induced ridge will pump Arctic air southward. And Voila! You get a cold spell in the eastern half of North America. In fact, there will probably be a few Arctic cold fronts coming in starting this weekend and especially next week.

The cold air might last, at least on and off, for several weeks, and maybe into a good chunk of the winter. Capital Weather Gang says something called the Arctic Oscillation will ensure some cold blasts to come. 

The Arctic Oscillation is a measure of the strength of the polar jet stream. If that jet stream is strong, that jet stream acts a bit like a dam, keeping Arctic air masses from flowing southward into the United States.

If the Arctic Oscillation is measured as negative, that means the polar jet stream is weak. Arctic cold air can blast through that jet stream dam and flow down into the United States. That's what happened last winter. The Arctic Oscillation was in negative territory much of the winter, the polar jet stream was weak, so we got repeated blasts of frigid air.

Another factor that could keep the eastern United States chilled is record warm Pacific Ocean water off the Pacific Northwest coast. 

Sometimes, this warm water can help maintain that ridge of higher atmospheric pressure in the western U.S. That ridge often, but does not always, mean a dip in the jet stream in the East.

As I've already said, such a dip leads to cold temperatures.

We'll see how all this plays out.

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