December 10, 2013: The Big Picture

The Big Picture

Below is a simple visual illustration of why the nation has been so cold lately and why we've been seeing these quick moving, weak systems this week.

Here are the key points:

A) Big dip in the jet stream over the US/Canada
-Allowing an Arctic air mass to flow southward around high and low pressures

B) Strong tropical high pressure and subtropical air mass across the Caribbean
-Preventing cold air from advancing past the southeast US

C) The two air masses meet across the southeastern US
-Resulting in a "river" of moisture from Pacific Mexico, across the eastern US

The combined result has been dramatically cold temperatures across the country (except Florida). The heart of the cold air will shift into the northeast by the end of the week.

This set up has also been responsible for the three Texas-to-Maine storms over the past week. Today's system is circled in yellow over the eastern US, while the potential nor'easter for this weekend is located off the coast of southern California.

Yesterday's system is already half way across the Atlantic… the jet stream is greatly accelerated between the arctic air mass and the tropical air mass.

Click the picture for the current looping satellite image.

The jet stream regularly has dips and blips in its pattern that result in cold/warm spells, although this latest one has been notably strong and persistent.

These dips and blips circle the globe continuously. The fact that this one has been around for over a weak now, suggests that it'll probably be moderating somewhat for next week as the heart of the cold air continues to shift eastward.

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