Monday, July 29, 2013

2013-2014 Winter Update: Polar Vortex Likely to be Anomalously Weak This Winter

The polar vortex, a tight low pressure system in the Arctic Circle whose strength determines how much cold air North America may receive in the winter, appears to be headed for a weaker than normal stature this winter.

Two factors are contributing to this new development: the QBO and the stratosphere.

The QBO, also known as the Quasi-Biennial Oscillation, is an atmospheric oscillation that has a positive and negative phase. In the positive phase, a certain wind pattern in the stratosphere enhances the polar vortex, which in turn restricts cold air that may move to North America. On the other hand, the negative QBO permits a weaker polar vortex, resulting in more opportunities for cold weather in the winter.

This image may look a little intimidating, but bear with me, I'll explain it. This chart, developed by Mike Ventrice, shows eight different phases the QBO can take. As is shown on the left and right sides of this diagram, Phases 7, 8, 1 and 2 tend to be associated with the Easterly (Negative) QBO, while Phases 3, 4, 5 and 6 correspond with the Westerly (Positive) QBO. As the chart tells, we are in the mature stage of this positive QBO, something winter weather lovers don't want to see when winter comes around. I posted a few days ago about how the positive QBO is surviving in a very hostile environment, and this should allow the mature +QBO to stay close to the circle in the middle of the chart (this circle indicates the QBO is too weak to be in a certain phase) as it progresses into Phases 6, 7 and 8 by late fall. When November rolls around, I expect the QBO to be transitioning to a negative phase, which will give the green light for a weaker polar vortex.

While the QBO is in kind of a wait-and-see mode for when/if it will move to its Easterly (negative) phase, the current lower stratosphere temperatures are already hinting at a weaker than normal polar vortex this winter.

This image shows past observed temperatures at the 70 millibar level in the stratosphere; considering the stratosphere runs from the 100mb level to the 1mb level, these temperatures are considered to be in the lower stratosphere. Looking at the most recent plot of the red line (observed temperatures), we see it to be above the green dashed line, which defines the average temperature for that time of year. This means the stratosphere is running warmer than normal this summer. A warmer than normal stratosphere in the winter means the polar vortex is favored to be weaker than normal- in the same sense, below normal stratospheric temperatures would favor a stronger than normal polar vortex, and thus fewer opportunities for cold weather in lower latitudes of the northern hemisphere.

When looking at past years with stratospheric temperatures comparable to what we have seen this past spring and into summer, the following years came up:

-2003
-1997

So, I took a look at the winters of 2003-2004 and 1997-1998 in the stratosphere. Both winters had rather significant stratospheric warming events in the early winter, with warmings continuing into the later winter. This bodes well for the idea of a weaker than normal polar vortex this winter.

A new item I found was how the winter stratosphere (December-January-February) tends to reflect stratospheric height anomalies in the summer months (June-July-August).

Analysis of the geopotential height anomalies for the stratosphere from June 1 to July 26 shows a very strong tendency for positive height anomalies over the Northern Hemisphere. The strongest positive anomalies are observed over northeast Asia into Alaska and the Bering Sea. Lower height anomalies are displayed over Greenland and into eastern North America. While this summer to winter stratosphere correlation does not necessarily keep location in mind, the general gist you can get out of this image is that we are likely going to see positive height anomalies (high pressure) battling the polar vortex during the upcoming winter, aiding in the bid to weaken the vortex. If we see these positive height anomalies continue through August, I will be more comfortable with this idea of a weaker polar vortex for the upcoming winter.

The QBO moving from positive to negative (if not neutral-negative), along with an already-favorable stratosphere, tells me the chances of an anomalously weak polar vortex are on the 'likely' side.

Andrew

18 comments:

Anonymous said...

Stilk a littke far out but In addition, i think we are seeing the presence of a +PDO/+PNA and warm SSTAs in northern Atlantic ( creating a ridge in the North atlantic) strongly fsvors the presence of a deep trough over eastern US, allowing for the cold air from the polar vortex to make it's way on down, and for storms to ride uo the coast.

Anonymous said...

Great no snow again

Anonymous said...

what do you use to make your own maps?

Andrew said...

Anonymous at 2:37: I never said anything about snow- this strictly relates to cold weather potential.

Andrew said...

None of these maps are of my creation, although if you want the source of some of these graphics I can provide the links to you.

Anonymous said...

This will work for me, I can handle the cold, but snow..now that's a different story! Buying sweaters now while they are cheap to buy!
Thank you Andrew for all your hard work that goes into making this a great place to come to!
bree

Frank-o said...

Love the post! This is stuff you can really sink your teeth into. We all should know by now that......Cold does not equal snow folks......

Patrick Towey said...

please provide a link to these charts

Anonymous said...

When do you expect your official forecast to come out?

Andrew said...

Anonymous at 8:03: Probably in mid September, I do not have an actual date yet.

Anonymous said...

Do you think this winter will be more of a slushy snow rather than a light fluffy type snow or do you think it will be more of a mild rainy winter? We have not had any really winters in the past 2 years.
We have had a few minor snowstorms but nothing big. Mainly it has just been wet snow and rain with temperatures ranging from the mid 30s into the low 50s on average the past 2 years. Do you think this coming winter will be anything like that?

midatlanticweather said...

Nice post. I am midaltnaitcweather (I have commented here before?. I am a forecaster (still learning) and I am learning more and more about the polar vortex. What are your winter thoughts? Please check out my YouTube channel and my website.
YouTube Channel:

http://www.youtube.com/user/midatlanticwxprogram

Website:

http://unitedstatesweatherplus.wordpress.com/

John Foust said...

Is the QBO phase chart available to public?

Andrew said...

Anonymous at 9:11: There is no way to tell the quality of snow right now, and I'm not confident in issuing winter forecasts for specific locations yet.

midatlanticweather: My current thoughts are on the Preliminary winter forecast link just below the blog's logo on this page.

John: This is the phase space: http://www.atmos.albany.edu/student/ventrice/real_time/QBO_phases.png

Anonymous said...

I need some clarification because. I've heard contradicting opinions from some people. If you wanted snow and cold in the east (mid atlantic) , would you want a warm/positive PDO or a cold/negative PDO?

Andrew said...

Anonymous at 1:53: Positive PDO gives the east coast above normal precipitation.

Anonymous said...

Wow you were spot on :)

Susan Kelly said...

It must be exciting to see your analysis and predictions unfolding.Still who would have thought Niagara Falls would freeze. While I symphatise with those who are in the midst of it,it is a beautiful and awesome sight from a warmer place. Where is heading now?