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.
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)
Winter 2016-17 has featured a Positive Eastern Pacific Oscillation (EPO):
Compare the image above with a Negative Eastern Pacific Oscillation (EPO):
Winter 2016-17 has also featured a Positive NAO (North Atlantic Oscillation:
- Warmth in the East, Cooler in the West
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
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**