In Pictures: Why has it been so Mild (So Far) this Winter?

Buckle your seat belts… the early Spring weather may soon be a distant memory. Summer 2016 rolled into the Fall… Fall 2016 weather rolled into Winter… Is Winter 2017 just about to get started in the Eastern United States from the Mid-west to the Mid-Atlantic? 

So we’ve shattered records dating back to the 1930s, probably 90% of the folks you talk to have claimed that the Winter that wasn’t (except for a period in early to mid December with brutally cold temperatures) is done and Spring is here.

Folks there is a reason why it has been warm and it has everything to do with the Teleconnections, or upper level pattern in the highest level of the troposphere (the layer of the atmosphere where weather occurs).  I have always stated that Ocean temperatures drive the jet stream behavior.

The “Warm blob of warm water” off of the Pacific Northwest coast last winter (also known as a warm PDO) drove the jet stream northward into Alaska allowing a dominant ridge of high pressure to be entrenched along the west coast.  In physics, what goes up must come down and the cold arctic air (you’ve heard this called the “Polar Vortex” gets displaced and dives into the eastern half of the lower 48.

So far this “winter” has featured mild Pacific west to east flow across much of the nation while the west coast has been inundated with storm after storm. Thankfully this pattern has provided California historic drought relief.  Why do ocean temperatures drive the jet stream? Because warm water causes the air above it to warm and rise and cold water causes the air above it to cool and sink. When you have warm and cold water sitting right next to each other in the eastern Pacific (image below courtesy NOAA/ESRL) the jet stream travels right along the zone of temperature contrast. So in the image below the Jet would drive just north of Hawaii and then rapidly lift northward along the western coast of North-America before diving back south into the eastern United States. 

pdo_warm

So enough weather-geek jargon… there’s a fantastic website called Mad US Teleconnections where you can see how temperatures behave during the 12 month calendar year based upon the various phases of the teleconnections (North-Atlantic-Oscillation (NAO), Pacific North American Oscillation (PNA), Arctic Oscillation (AO), Eastern Pacific Oscillation (EPO), and Western Pacific Oscillation (WPO). 

So far, Winter 2016-17 has featured a Negative PNA (Pacific North-America) Oscillation:

  • Notice the “warmth” over the southeast & Mid-Atlantic in January during a negative PNA (the same is true for December through March)

mt_pna_negative

Winter 2016-17 has featured a Positive  Eastern Pacific Oscillation (EPO):

epo_positive

Compare the image above with a Negative Eastern Pacific Oscillation (EPO):

neg_epo

Winter 2016-17 has also featured a Positive NAO (North Atlantic Oscillation:

  • Warmth in the East, Cooler in the West

mt_nao_positive

Finally Winter 2016-17 has featured a Positive Arctic Oscillation (AO):

  • Warmer than normal temperatures across much of the Nation as bitterly cold air is locked up in Canada

mt_ao_positive

So there you have it, when your friends talk about how mild its been and wonder why… you can educate them about Sea Surface Temperatures (SST) anomalies (colder or warmer than average) and how they drive the Jet Stream (the overall teleconnection pattern). 

 

**In my next post I am going to look at what the models are forecasting as we round out February and head into March and what may be just on the horizon… hint: Not time to throw in the towel yet**

3 Replies to “In Pictures: Why has it been so Mild (So Far) this Winter?”

  1. At least it looks like you are not entirely blaming the mild winter on global warming or climate change, as some people have.

    For you information, the the 1941-1942 winter had only 2.0″ of snow as of March 28th, which would have been a record low at the time. But 11.5″ fell on March 29th.

    Two other winters, 1959-1960 and 1913-14 had NO measurable snow going into February 13th. But 1959-1960 ended up with 24″ and 1913-1914 ended up with 28″.

    Just goes to show, these patterns can sometimes suddenly flip with a vengeance!

    Like

    1. Exactly. They can flip quickly. And I’m personally mad at the Warm PDO for flipping without asking our permission 🙂

      Like

    2. So glad someone else said it. For example, I enjoy Capital Weather Gang’s posts, but they love to pinpoint warm weather during winter, and the commenters constantly say global warming/climate change, and I’m sitting there like “but even back through the 1940s there have been Jan/Feb days in 60s and 70s…” I also don’t like that they fail to give an explanation for the warm winter, whereas Tim explains it at length. Love it! Context is important.

      Like

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