Unleashing the Arctic Cold
Mother Nature let us off easy with a mild December across the majority of the United States but some impressive cold air arriving this week is bouncing many of us back to reality. But hey, it’s January…it should be cold!
The graphic above shows a computer weather model depiction of temperature across the United States at 850 millibars or roughly 5000 feet above the surface from Monday (1/5) morning to Thursday (1/8) morning. This animation isn’t meant to show you the temperature at the surface but hopefully gives you a good idea of the penetration of the cold air as it descends over the Plains, Midwest, South and the East Coast. Notice the blue and purple colors push southward into the Gulf States and the Southeast. Meanwhile, the most intense pocket of arctic air — colored red, orange, and yellow — swings across the Upper Midwest, Great Lakes, and finally New England during the same time period.
In winter, a very strong area of high pressure translates to extreme cold and a very dry air mass. The above graphic is a model depiction of surface pressure for Wednesday afternoon (1/7). When you begin to talk about surface pressure of 1040 to 1050 millibars in winter, you’re dealing with some brutal cold; a bone-chilling air mass. But when you start talking about a surface pressure nearing 1060 millibars (centered over Nebraska), well then, now you’re dealing with a truly remarkable cold air mass (and some remarkably dry air to boot). A 1060 millibar pressure reading equates to about 31.30 inches of mercury (inHG) — a measuring unit that you might be more familiar with. But no matter how you measure air pressure, there’s a pretty good chance that several high air pressure records will fall this week in the central U.S. as that monster high sets up shop. The record high pressure in the United States was set in Miles City, Montana on December 24, 1983 when the sea-level pressure reached 1064 millibars or 31.40 inHG.
The above animation shows forecast low temperature values for Tuesday, Wednesday, and Thursday morning as predicted by The Weather Channel. The first thing that pops out at you is that the northern Plains, Upper Midwest, Great Lakes, and northern New England will all be dominated by subzero morning lows during this time period. Something that also stands out is just how cold a majority of the United States will be by Thursday morning. Single digit readings wil reach the Tenessee Valley while subfreezing values will reach as far south as the Gulf Coast. There may not be many record lows set — due to the fact that the record low “bar” is already set very low in January — but it certainly will be the coldest air of the season thus far. Moreover, after a fairly mild December this arctic air mass may be a bit of a shock to the system.