As the month closes, the Polar Vortex is set to trigger an explosive cyclogenesis event, with a Nor’Easter unfolding just off the U.S. Southeast coast. A rapidly deepening cyclone takes place as a powerful subtropical jet streak collides with a sharply displaced lobe of Arctic air diving south from Canada.
The result will be a potentially high-impact surface low undergoing rapid intensification, with central pressure forecast to fall more than 24 millibars in 24 hours. This is known as a bomb cyclone.
Its potential track and impact are still a bit uncertain on Sunday, but it appears likely to bring violent winter weather from the Outer Banks to interior New England and coastal Maine. Severe winds exceeding 65 mph, blizzard conditions, coastal flooding, and severe travel disruptions may occur across the Northeast corridor.
While the East Coast could see more heavy snowfall, blizzards, severe winds, and coastal flooding from a strengthening Nor’easter, the Southeast and Florida face a sharp, potentially record-breaking temperature drop over the weekend.
Florida is forecast to experience one of the coldest morning lows in decades on Sunday. With freezing temperatures down to Miami. The last subfreezing temperature in southern Florida occurred in December 1989 during one of the most exceptional cold spells.
The reason is the significant disruption of the Polar Vortex, which releases a secondary wave of a deep Arctic air intrusion behind the bomb cyclone storm’s primary circulation. A full-scale displacement of Arctic air into the East and Southeast U.S. brings a prolonged hard freeze.
According to the NOAA 6-10 day temperature outlook, temperatures will remain below normal for at least another week, with dangerous wind chills across the East Coast as the Nor’Easter forms over the weekend and winds increase.
Before we dig into the details of the potentially impactful new Winter Storm associated with the explosive Nor’Easter bomb cyclone, it is essential to understand the background mechanisms governing the Polar Vortex.
Note that this is the main trigger of rapid weather changes and intense Arctic outbreaks across Canada and the United States during winter, bringing extreme cold deep into the South, towards the Gulf Coast.
What is the Polar Vortex?
The Earth’s atmosphere has six layers. Most of the dynamics of our daily weather occur in the lowest two layers of the atmosphere, the troposphere and the stratosphere.
The troposphere is the layer closest to the Earth’s surface. It is about 12 km deep and extends from the ground up high into the sky. Depending on where you live, its depth varies from around 8 km to almost 20 km. The troposphere is deepest over the equatorial region and becomes much thinner over the North and South poles.
Above this layer is a much deeper one known as the Stratosphere, an 11-50 km thick layer of arid air. Another essential feature in the stratosphere, which makes our weather even more variable, often triggers significant, large-scale, long-lasting winter weather events.
This is the Polar Vortex—an enormous, tri-dimensional ring of powerful winds moving through the sky above us. The Polar Vortex is spinning around the North Pole, grazing through the air at about 20-50 km above the Earth’s surface with violent wind speeds.
How and when does the Polar Vortex form?
Due to the Earth’s inclination, the polar regions receive much less energy from the Sun during the fall months. This makes the cooling over the northern areas more robust. As a result, polar nights can last several consecutive months, followed by days without sunlight.
While temperatures in the polar regions are dropping into a deep freeze, the atmospheric layers farther to the south are still relatively warm because they receive more of the Sun’s energy at the same time. Therefore, the south’s equatorial layers remain much warmer than the areas farther north, leading to a high-temperature contrast.
Cooling the polar regions also lowers the ambient surface pressure, and a similar weather process occurs in the stratosphere. The temperature difference between the North Pole and the equatorial areas increases across both layers.
This creates a large, low-pressure cyclonic circulation across the polar stratosphere, which gives it its famous name—the Polar Vortex.
As shown in the image above, we monitor two atmospheric layers during wintertime: the troposphere and the stratosphere. The first is the lowest layer, and the second is at a higher altitude. The Polar Vortex rises through both layers, but with different strengths, shapes, and impacts.
For this reason, we separate the entire Polar Vortex into an upper (stratospheric) and a lower (tropospheric) part. When the Polar Vortex is strong, it traps colder air in the polar regions, preventing its escape and creating milder conditions for most of the United States, Europe, and other mid-latitudes.
But when the Polar Vortex gets disrupted or even entirely collapses, it can’t fully contain the cold air, which can now easily escape from the polar regions into the United States or other mid-latitude regions. Below is an example of how a disrupted Polar Vortex brings cold polar air into the United States and Europe.
We have experienced this in Asia, Canada, the U.S., and sometimes Europe in recent years. The vortex aloft has been significantly disrupted this season, and when its lobe shifts away from the North Pole, the extreme cold grips the North American continent.
A deep core of the southern Polar Vortex lobe digs into the Southeast U.S. and Florida
As mentioned earlier, a significant disruption and the potential collapse of the Polar Vortex is underway and will follow through early February.
This is sending deep cold Arctic intrusions far south across North America, with one blasting into the Southeast U.S. over the weekend.
It leads to a major displacement of the polar jet stream, with its winds digging deep south into the Gulf region as the strong blocking High persists over the western CONUS and the North Pacific.
An amplified jet stream follows after the collision with the subtropical air masses, developing violent winds in the upper levels.
It helps drag the Arctic cold air masses far south, spreading across the Southeast and the Gulf Coast by the weekend.
Temperatures will be extremely low for the region, with 30-40 °F below normal from Louisiana and Mississippi to Alabama, Georgia, and Florida.
The core of the cold could challenge some mid-level historic records for the region. This really is unusually deep cold this far south.
And this is where the fun begins. The amplified jet stream, with the clash of Arctic cold and warmer subtropical air masses, leads to an explosive development of the surface low off the Southeast coast. A bombogenesis Nor’Easter storm occurs, with a rapid pressure drop as the low strengthens along the East Coast.
The cold pool over the eastern two-thirds of the country raises surface pressure, creating a strong pressure gradient with the deepening low over the Atlantic coast.
This will increase the wind field from the East Coast and the Mid-Atlantic states to the Northeast U.S. and to Nova Scotia, Canada. Leading to blowing snow and, in case of new snowfall, also violent blizzard conditions and whiteouts.
Nor’Easter could bring major snow and intense blizzard conditions for the East Coast
Despite some uncertainties about the storm’s track on Saturday, the potential for a highly impactful snow and blizzard is increasing. The general weather model consensus, with ECMWF and GFS, hints at an impact on the Outer Banks, with the GFS solution more aggressive.
The following snowfall chart from the GFS model hints at where the snowstorm’s worst impact could be. It should be noted that it all depends on how close to the East Coast the core of the bomb cyclone Nor’Easter passes. The further west it goes, the more significant the impact will be.
The chart suggests that North Carolina and Virginia could be in the path of a violent winter storm. This will likely bring more snow to the areas affected by the recent Winter Storm Fern.
More deep snow is possible over Raleigh, Washington, D.C., including New York City, Rhode Island, and Boston, over the weekend.
What’s concerning is the strength of the near-surface winds, as the pressure and temperature difference between the center low and the Southeast U.S. will be extreme. This should result in particularly severe winds.
Although the exact position of the low is still uncertain, if the low sits closer to the coast, the violent winds will be damaging to trees and infrastructure.
Combined with heavy snow, severe blizzard conditions would result in major travel disruptions, whiteout conditions, high snow drifts, and major delays. Including more flight cancellations.
Unusually deep cold core sends record-challenging temperatures into the Southeast and Florida
The core of the Polar Vortex lobe aloft will be unusually deep, and it will dig very far south across North America, spreading extreme cold across the Southeast U.S., including the Gulf Coast and Florida. Morning lows over the weekend will be frigid for 250+ million people east of the Rockies.
Saturday morning temperatures will be in the single digits across the Midwest, the Great Lakes, the Ohio and Tennessee Valleys, and the Northeast U.S., possibly even in negative degrees F in Indiana and Michigan. In the tens for the rest, low to mid-20s for the High Plains and Texas.
A closer look across the Southeast U.S. suggests the cold will be particularly extreme, also along the Gulf Coast and across all of Florida. Morning lows will reach mid-20s in central Florida.
Further south, freezing temperatures and morning frosts will be possible in extreme southern Florida, including Miami. This is extremely low for the state, and the last time a subfreezing temperature this low occurred in Florida was in December 1989.
Saturday morning, low temperatures could challenge multiple station records across Florida.
To conclude, the upcoming secondary wave of the Arctic cold blast will be quite intense for the Southeast U.S. It will trigger a violent bomb cyclone, acting as a Nor’Easter winter storm off the East Coast, and could bring intense blizzards and heavy snow with damaging winds to the Outer Banks.
The cold across the Southeast U.S. will be brief but intense. The following chart shows the temperature forecast for Atlanta (upper chart) and Washington, D.C. (lower chart). We can see that both regions are under deep cold for at least another week, while Atlanta hints at a deep core over the weekend.
As we head into February, we will continue monitoring the ongoing progressive and active weather pattern across Canada and the United States. The potential collapse of the Polar Vortex is likely to trigger more frigid cold outbreaks and winter storms with deep snow across North America in the coming weeks.
Stay tuned for further updates.
Windy, PivotalWeather, and Wxcharts provided images used in this article.