An intense outbreak of cold weather will descend on the eastern two-thirds of the country next week, with widespread low temperatures in the single digits and below zero for a couple of days. Lows in the teens are even possible as far south as Alabama and Mississippi.
People are still a little...touchy...about the polar vortex after last winter. I don't think we should be afraid of using the term as long as it's responsible and in the proper context. Let's get it out of the way right now—yes, this cold outbreak will be influenced in part by the polar vortex, but nowhere near on the scale we saw last winter. The best way to describe it is a glancing blow.
The polar vortex is a persistent, large-scale counterclockwise circulation around the Arctic that acts like a moat keeping bitterly cold air confined to the far north. The vortex often looks like a smooth belt, but every once and a while the circulation will become wavy, allowing cold air to flow south out of the Arctic. Last year, the vortex broke into several upper-level lows, one of which rotated over Ontario and the Great Lakes, causing a prolonged period of extremely cold weather in the United States.
This time around, the main circulation will stay safely up by Greenland, but a trough extending off of the upper-level low will swing down through the Great Lakes and Northeastern United States, facilitating low temperatures at or below zero for a large portion of the Midwest and Northeast for a few days next week.
Using this morning's run of the GFS model, here's a look at the 500 millibar level of the atmosphere (16,000-18,000 feet above sea level) beginning around 7:00 AM EST on Tuesday and ending before sunrise on Friday. Cooler colors show lower heights (correlating roughly to lower surface pressure) and warmer colors show higher heights. The model shows the main circulation of the polar vortex firmly planted over Baffin Bay, with a trough extending from the low and moving through Ontario, the Great Lakes, and the Northeast between Tuesday and Friday.
People don't much care for nuance, and since the sound of chattering teeth is too hard to type out, the media will call this the second coming of the polar vortex. Ignore that noise. It really is more of a glancing blow than anything like what we saw last winter.
It's going to get cold, though.
How cold will it get? Again, from the GFS, low temperatures on Thursday morning could dip to almost 40 degrees below normal around Lake Michigan. Chicago's average low for January 8 is 17°F. The GFS model is trying to paint lows on Thursday morning dipping to -18°F in the Windy City. Normally I would throw out these temperatures as too extreme, but this morning's run of the European model is corroborating what the GFS predicts, if not five to ten degrees warmer on the whole.
Here's a look at model-predicted high and low temperatures for New York City over the next couple of days:
For now, forecasters aren't exactly hopping on the record cold bandwagon yet, but if the weather models continue to show these dangerously cold temperatures through the weekend, it's a distinct possibility that many residents in the interior Northeast, and especially the Great Lakes and Midwest, will wake up to temperatures below zero one or more mornings next week.
Regardless of how cold actual temperatures wind up getting, the pattern is clearly shifting to the miserable cold pattern that we should see around this time of the year. Many of us have enjoyed days where you can almost get away with not wearing a coat when you go outside, but those are done for the foreseeable future. We're about to realize how easy we've had it these past few weeks.