Is Winter Finally On The Way ??
Are beginning to transition into a more winter like pattern it appears as we head into December ??
That is certainly a good question, but to be fair.. that’s when winter is suppose to start !!
Let us begin to look at the larger state of the climate based on El Nino-Southern Oscillation Phase. We are currently in a La Nina State which means waters in the Pacific Equatorial region are below normal in temperature. Below is somewhat of a generalistic look of usual conditions for La Nina type pattern.
Now there are multiple on-going factors that need to be taken in consideration, and obvious La Nina conditions differ from West Based to East Based and with other factors that are in play. Forecasting long range are ‘best guess’ based on what current conditions are likely to be.
Here is a reminder of the 2017 – 2018 Winter Outlook from CPC:
(Click either pic to go to the NOAA CPC Page for more detail)
The major other factors are what we call teleconnection patterns. Teleconnection refers to a recurring and persistent, large-scale pattern of pressure / circulation anomalies that spans vast geographical areas in the atmosphere.
So lets try to go through and give you a graphical representation of each, and try to explain how a -NAO -AO and +PNA are the best set up for a Mid-Atlantic / East Coast for winter storm setup.
Below is a look at characteristics of a Negative / Positive Arctic Oscillation (AO)
You can see here in a negative phase that the cold in the stratosphere is basically displaced into Canada and North America.
Here is a graphical representation of a North Atlantic Oscillation (NAO) and its general effects:
A Negative NAO is also sometimes referred as the Greenland Block , East Based NAO because high pressure establishes itself there allowing for the strongest flow of cold into the Mid Atlantic. West based NAO where high is positioned move over Canada is little less favorable.
… and Finally A Look at the Pacific North American (PNA) Pattern
Positive PNA is also sometimes referred to as a ‘zonal flow’ usually brings milder conditions from the west straight along to the east.
So wait then, why did we see snow then here in December of 2013 where the patterns didint match any of these and we still got good snow fall totals ???
There is another pattern called the East Pacific Oscillation (EPO)
The EPO is the high altitude wind flow over the Eastern Pacific which is influenced by the ocean temps.. When the EPO is in a positive phase, there is usually troughing on the West Coast, while milder air engulfs the inland and Eastern part of the country. The positive EPO limits troughs in the East. When the EPO is in a negative phase it has the opposite effect on the East Coast where a -EPO encourages a northwesterly flow from Canada into the Eastern part of the U.S, allowing for cold air to intrude, but without the assistance of a stronger -AO or -NAO we end up with more transient shots of cold air that usually support snow more west of the coastal plain as we saw in 2013.
Water Temperatures – This early into the year, water temps usually dont help us on the coastal plain that much. It is usually not till we get more into the heart of the winter season when water temps get cooler and have a less dramatic effect on potential snow storms.
Finally Storm Track – Inland storms also favor snow to west and rain to the east.. with a south to south west wind bring warm temps during the storm, and then cold air as the system moves out with slight chance of snow on the back-end.
Okay so what are we seeing today that may be indication that winter is coming ?
AO – Trending Negative
NAO – Trending Neutral to Negative PNA – Positive
EPO – Going Negative
So in summary as it looks as we are beginning a transition to more colder pattern it could also spell a more wintry one as well. Yet, we dont want to get ahead of ourselves and be as bold to say a snowy harsh winter is on the way. Just because we are trending colder does not mean we will be getting a snow storm soon. Water temps right now make coastal plains not a good bet for snow especially if there’s a prevailing east wind and we really do not know how long or consistent this pattern will remain.
All this tells us is that cold is on the way in the short term, ‘weather’ or not the patterns line up to give us a chance of some wintry weather, well that’s just yet to be seen. Will winter pattern drag thru the remainder of the winter months ? Again a great big unknown but ENSO conditions don’t necessarily support it.
So in closing.. remember to get that fire wood stacked.. ensure your winter weather equipment and supplies are up top date… prep your travel with a winter kit for the car that includes extra blankets, shovel, heat warmers, de-icer, etc. You cant go wrong by being prepared !