Much of the eastern U.S. is about to plunge into the coldest wave of Arctic air we've seen this winter, and for many, it could feature more sustained cold temperatures than we saw during the Great Polar Vortex Panic of 2014. If that isn't bad enough, the east could see a couple of disruptive winter storms next week.
I've seen some meteorologists bicker on Twitter over whether or not the upcoming blast of cold is the result of the polar vortex or just a regular ol' hellish cold snap. Before we get into the details of the impending frozen doom, we should take a look at what happened last year in order provide perspective for this weekend's weather.
What Is the Polar Vortex?
The polar vortex is a persistent upper-level circulation (essentially a low pressure system) that typically circles the Arctic like a belt. The polar vortex acts like a moat that keeps bitterly cold air locked into place in the far northern latitudes where it belongs. Every once and a while, the polar vortex circulation will become unstable, growing wavy with ridges and troughs, or even breaking apart into standalone (or "cut-off") upper-level lows. When one of these troughs or lows dips down over the lower latitudes, it can bring with it very cold air from the Arctic, producing some of the ugliest cold snaps winter can throw at us.
The polar vortex is nothing new; it was discovered (and named) back in the 1800s, long before CNN and ominous transition graphics were a twinkle in Ted Turner's eye. Its scary-sounding name and the existence of social media created a perfect storm of legitimate science becoming hype. The media overused the term so badly last year that meteorologists and weather geeks have to be careful using it today so people don't tune them out or start ruthlessly mocking them.
The Great Polar Vortex Panic of 2014
Last year, a piece of the polar vortex broke away and swung down over the upper Midwest and Great Lakes, allowing record-breaking levels of cold air to pour into the central and eastern United States from Canada. The resulting spell of cold weather produced low temperatures far below zero—up to -20°F in many spots in the upper Midwest—before the bitter chill moved east towards the Ohio Valley and Northeast.
January 7, 2014 was by far the worst day of the outbreak, with low temperatures the following night dipping into the single digits as far south as Georgia and Alabama. Atlanta's low temperature on the morning of January 8 was just 6°F. Even down in typically-muggy Mobile, Alabama, the low dropped to 14°F.
Here are some more lows we saw that morning:
Washington D.C.: 6°F
Greensboro, N.C.: 5°F
New York City: 4°F
Syracuse, N.Y.: 0°F
Buffalo, N.Y.: -5°F
Pittsburgh, PA: -9°F
Cleveland, OH: -11°F
Outside of the upper Midwest, the incredibly cold air was a two-day shot before it rotated out and more mild air returned. The situation is different this year, but it will result in a much more sustained blast of cold air than we saw last year.
This Weekend's Cold Snap
An upper-level low will cycle down from the northern latitudes and swing across the Great Lakes and Northeast this weekend, bringing with it some very low temperatures. The most common description I've seen from meteorologists is that this is a "lobe" of the polar vortex dipping down into southern Canada and the northern United States.
Here's a look at the height of the 500 millibar level of the atmosphere across the Northern Hemisphere, shown in decameters. Lower heights roughly correspond to lower pressure; much as 1013.25 millibars is standard pressure at sea level, 540 decameters (5400 meters, or 17,716 feet) is the standard height for the 500 millibar level. North America is towards the bottom-center of the map, Europe and Africa are on the right, and Asia is at the top of the map.
I've drawn a rough outline of the polar vortex and its belt of influence, such as it exists, showing trough/lobe/tentacle does have at least a little to do with the feature.
How cold will it get? Cold. Here are the forecast highs/lows from the National Weather Service as of Thursday afternoon.
The cold air won't be quite as pervasive in the southern United States as it was last year, but the temperatures are definitely colder this time around in the Northeast than they were last year. Across places that see the worst temperatures this time around, the cold air will stick around much longer: look at the brutal temperatures forecast for Cleveland, where the highs/lows were 4/-11 (Jan. 7) and 21/5 (Jan. 8) during last year's polarvortexmageddon.
Remember that these are just air temperatures—wind chill values will be much, much lower. Wind chills of -30°F or colder are possible in the coldest spots, which would allow frostbite to develop in just a few minutes on any exposed skin.
Next Week's Cold Snap
After a small rebound on Tuesday, temperatures will bottom out once again as another upper-level trough digs down into the United States. This system will bring cold weather farther south than the one on Sunday, but it won't last more than two days. Again, we could see temperatures dip into the single digits or below zero on Tuesday/Wednesday night in the central U.S., and Wednesday/Thursday night in the Northeast. Wednesday morning lows could drop into the single digits as far south as Arkansas, Mississippi, and Alabama.
There will be a few chances for heavy snow over the next week. The first opportunity for heavy snow will occur with a major storm system developing during the height of the cold snap on Sunday, where else?, in New England.
The models are showing a very strong nor'easter developing off the southeastern coast of New England, which would place the heaviest snow (and potential blizzard conditions) in hard-hit cities like Boston, Manchester, Portsmouth, Portland, and Bangor. Pretty much everyone who doesn't need snow will see snow this weekend. Snowfall totals will likely exceed one foot in coastal areas that see the heaviest snow bands—Boston could see up to a foot (or even more) from the storm.
Update 4:44 PM: Shortly before the publication of this post, NWS Boston issued a blizzard watch for coastal Massachusetts, including Boston. 8 to 14 inches of snow are possible from the storm along with a period of blizzard conditions on Saturday evening through Sunday evening. The watch extends from Plymouth, Massachusetts, all the way north through Maine to the Canadian border. Other cities included in the watch are Portsmouth, New Hampshire, and Portland, Augusta, and Bangor in Maine.
Here's the watch for New Hampshire and southern Maine, including the potential for 12 to 16 inches of snow. The blizzard watch for the area around Bangor also advises of the potential for 12 to 16 inches of snow.
In addition to our Americentric weather forecasts, if you live or know someone who lives in the Canadian Maritimes, this could be a devastating storm for parts of New Brunswick, Nova Scotia, and Prince Edward Island. Sustained blizzard conditions with snowfall accumulations of one to two feet will make travel impossible and lead to widespread power outages, especially in rural areas. Intense waves and coastal flooding are also likely on south/southeast-facing shores.
We're going to see a more classic and traditional nor'easter situation develop on Tuesday and Wednesday. The models currently show an area of low pressure developing near the Gulf Coast on Monday night and Tuesday, racing northeast into the cold air, which could produce a very dicey situation from Arkansas through the Tennessee Valley and up through the Mid-Atlantic and into New England. This morning's run of the GFS shows heavy snow falling across areas that don't often see heavy snow and ice, such as Mississippi and Alabama.
The storm will rapidly strengthen as it races towards New England, bringing along with it the potential for blizzard conditions if strong enough winds accompany the heavy snow. Blizzard conditions occur when winds of 35+ MPH create blowing snow that reduces visibility to one-quarter of a mile or lower for three or more consecutive hours. In other words, a blizzard is a sustained whiteout.
Given the delicate tango of warm and cold air through the atmosphere, it's going to be a few days before we know exactly who will see snow, ice, and rain from this system, but if you live in the southeast (and especially along the I-95 corridor), you need to watch this system like a hawk and prepare to alter or cancel plans towards the middle of next week.
There are 36 days until spring.