If you look at the title image, you'll see a map of the upper-level pattern. The black lines represent height contours at roughly 30,000 feet. The big dip you see in the West is called a trough. It's an area of low pressure. The ridge in the east represents an area of high pressure. What's happening is a big ridge of high pressure has developed in the Northern Pacific, leading to the dip in the polar jet in the West. Cold air from Canada has been rushing down into places like Los Angeles and Las Vegas, who typically don't see this cold weather. In fact, Los Angeles saw its lowest temperature in 22 years Monday morning. The low was 34 degrees. The related image shows the current temperature map early this morning and the cold in the West.
In the Northeast, Portland, Maine is expected to get to near 50 degrees Monday afternoon. Their normal high temperature is 31 degrees.
When we look at teleconnections in weather, one pattern comes to mind called the PNA, or Pacific/North American pattern. There is a positive phase and a negative phase. The negative phase is what we're seeing right now, a trough in the West and a ridge in the East.
This ridge out west breaks down through mid week and a warming trend will begin for the west coast and the bitter chill will move into the Northeast. Portland, Maine will go from near 50 Monday to the mid twenties for highs by Friday.
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