Explaining the "Polar Vortex": The Most Misused Weather Term of 2014

Courtesy of ABC News

It’s that time again. What time is that you may ask? The time of the year when extremely cold air that comes into our region is labeled a Polar Vortex.  Around this time of year, the media can sometimes go into a frenzy, repeatedly using this term. However, many times the word is not used correctly. So what exactly is a “Polar Vortex”?  

First off, the Polar Vortex is a low-pressure system that continuously circulates year round in the Arctic and Antarctic regions. It is worth noting that the Polar Vortex in-fact exists during the summer months; it’s just not as strong as it is in the winter. It extends from the middle troposphere (0-11km) into the stratosphere (12-50km) and rotates counter-clockwise in the Northern Hemisphere and clockwise in the Southern Hemisphere. The reason why you hear about it in the winter is because the center of low-pressure circulation strengthens in the wintertime. Occasionally a portion of the Vortex will migrate southward, which was the situation last week. In that scenario, the Polar Vortex weakened allowing a portion to migrate from the north into regions further south and gets absorbed into the jet stream. When this happens, portions of the United States experience dramatic episodes of cold air outbreaks. A further extreme situation is when the circulation of the Polar Vortex starts to collapse. As it collapses large portions of cold air break free and affect our region. This is what occurs when we have historic/record breaking Arctic air outbreaks, like we had last January. High winds can often accompany a Polar Vortex.

Courtesy of NASA

A large part of forecasting these Arctic air outbreaks is looking at the positioning of the jet stream. In the wintertime, the polar jet will dip further south than normal. The strengthening of the jet stream brings frigid air into a region of traditionally warmer air. This is a significant factor in the deepening and strengthening of low-pressure systems. These downward dips in the jet stream accompanied with polar Arctic air are important ingredients in fueling winter storms. During this event, the jet stream acts as a boundary between the cold, polar air masses in the north and the southern tropical air masses. The warmer air mass to the south is moist; and when it forms a front along a cold, dry air mass, strong winter storms are possible. The warm, moist air mass rises over the cold front allowing the moist air to cool. This is a key ingredient of the precipitation process. When precipitation begins to fall, the colder air mass at the surface provides the cold, frigid temperatures needed for frozen precipitation to develop in the form of snow and frozen rain.

          

          Hopefully, this article was able to clear up some misconceptions you may have had about this unique, but often misunderstood weather pattern. Every cold snap is not a product of a Polar Vortex. It is very possible for our region to experience a cold blast without it being accompanied by a Polar Vortex. It’s often that we are just under the influence of a polar Arctic air mass. Finally, when you do hear a forecast with the Polar Vortex, remember there can be varying extremes of air circulation. A weak vortex is much different than a collapsed Polar Vortex where a cold air mass is very large and temperatures significantly drop. Don’t always assume the worst, but it is still prudent to be prepared for extreme cold weather during the winter months! 

-Katie 

When will this latest "Polar Vortex" End?

During the past week, a blast of Arctic air has put the entire nation under an intense cold spell. Temperatures this past week dropped 30 to 40 degrees in one day in some areas with intense snowfall and winds were present all over the Rockies and Cascades. The question that everyone seems to be having about this Arctic Blast is, how long is this going to last? To answer, we have to look at the cause of such an anomaly in temperature for this time of year.

Picture representation of how the powerful Low of Nuri
helps create a large ridge which in turn pulls Arctic air southward

A large intense low-pressure system which was the remnants of Super Typhoon Nuri moved off the coast of Alaska around 2 weeks ago. This low-pressure system caused pressure readings as low as 925mb in the Aleutians, 70mph wind gusts and 50 foot waves. This system was strong enough to pull warm moist air up from the Pacific and drive warm air pole-ward.  This knocks the “polar vortex” or the pocket of very cold air, also known as the polar low, southward. With no strong weather pattern blocking its path, cold air can gain momentum and cause the entire polar jet to dip well into the Southern Plains.  This causes the blocking high that once was in the higher altitudes to descend to the Continental US, making it very hard to move. Cold air being dense and near the surface makes it very hard to move with such stable conditions. Highs in the Midwest and the Plains will remain in the 20s and teens, while the Northeast will remain in the 30s.

The worst of the frigid temperatures will slowly
make their way eastward through next week

So when will the Arctic Blast end for this region?-Well things are not exactly looking good at least in the short term forecast for this region for the cold. A new batch of cold air and high pressure is moving across the Ohio Valley and slowly making it over the Appalachians; that is something that does not happen often. This means even colder temperatures expected early next week with a likely chance we will see some precipitation (most likely in the form of just rain) on Sunday Night into Monday as the front passes through the region. This will mean blisteringly cold temperatures with highs barely making it out of the 30s on Tuesday and Wednesday. Slowly but surely though, this Arctic front will start to recede as a new system is starting to form in the Pacific Northwest which will push Eastward into next week. This weather system will bring warmer temperatures and rain throughout the region and is scheduled to arrive at the end of next weekend into the beginning of next week.

This is Day 7 of the GFS model showing a large low pressure disturbance in the Pacific Northwest.
It is something to keep an eye on. Notice the Orange line,
which is the 0 degree Celsius mark for the high for the day.
It has receded tremendously in the Western US by this point.

There are still many questions we have with the forecast moving forward, including a disturbance on Friday evening, which could lead to mixed precipitation depending on how things shape out. I did not want to go into too much detail regarding the different variables that go into the long range forecast quite yet as they are themselves still up in the air.

Summary: Cold will remain. Sunny skies and High Pressure most days, the second front will move through on Sunday Night bringing rain and a fresh batch of cold air. Colder next week. Friday’s weather will be of a mixed precipitation possibly depending on the temperature sounding. Late next weekend will be the break from the cold.

Any further questions? Feel free to message me or comment on the post! 

-James