While the East coast is freezing, the West will be warmer than usual

In the first week of 2018, a persistent Arctic air mass has forced temperatures in some places on the East Coast nearly 20-degrees below average. Meanwhile, parts of California and the West are nearly 20 degrees above average. Temperatures from east Texas up to the Dakotas are right on track, serving as a de facto thermal continental divide.

The jet stream is bulging north over western North America, flooding that region with mild Pacific Ocean air. Like a seesaw, the jet stream is then crashing south over eastern North America, allowing frigid air sourced from the Arctic to pour in. Meanwhile, the circulation around the massive ocean storm or bomb cyclone over the Atlantic (which rocked the East Coast with snow and wind) is further enhancing the flow of bitter cold air from the Arctic into the eastern U.S.

Cold air is more dense, which is one of the reasons that low pressure is literally low and sunken down near the ground. Hot air is less dense, and it expands more, which is why the high pressure is more like a dome.

The large variance between high pressure areas in the west and low pressure areas in the Northeast creates strong winds, which are blowing southeast out of Canada, across the Midwest and down into the Southeast US, bringing the cold, arctic air with them.

This latest cold snap started in late December. Between December 24 and Jan. 1 — the latest date that records are available nationwide from the Global Historical Climatological Network — more than 717 record lows were recorded, mostly throughout the Midwest, and Northeast. 662 record highs were recorded in the West, with some areas setting new records six out of the nine days.

As the arctic air continues flowing in the east, temperatures will average below freezing from North Carolina through Tennessee and Missouri northward.